taxonID	type	description	language	source
03D72F3EFFBCFFA5509ADE7A2AE9FCBD.taxon	description	urn: lsid: zoobank. org: act: F 959427 F- 762 B- 4344 - A 1 E 4 - 7 D 491 DD 99225 Figs 10 ‒ 14; Supp. file 1: Table S 2	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFBCFFA5509ADE7A2AE9FCBD.taxon	diagnosis	Morphological diagnosis Body slender and about 83 ‒ 107 µm long. Head wider than neck, separated from trunk by a distinct neck constriction. Cephalion clearly demarcated, epipleurae and hypopleurae only inconspicuously marked in head outline. Trunk widest at ca U 62, gradually tapers towards furca base (U 85). Mouth ventral, with two cuticular teeth. Pharynx with anterior and posterior dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, not overlapping, distributed in 10 – 12 columns, 17 scales per column. Dorsal surface covered from anterior end of hypopleurae (ca U 6) to neck constriction with fairly small scales bearing short spines. Neck caries broader scales with longer spines. Anterior trunk region bears similarly shaped, slightly bigger scales with posterior lobes closer together. Dorsolateral and lateral scales with elongated base and posterior lobes more divergent, spine with an inconspicuous denticle. Mid-trunk to terminal trunk region covered by (i) five horizontal rows of big, anteriorly tapered scales carrying very elongated, massive spines with a denticle and membrane and (ii) two horizontal rows of smaller, anteriorly rounded scales carrying significantly shorter spines with a denticle. Furca base short, lateral margins vaulted, furcal indentation U-shaped, adhesive tubes well-developed, diverging posteriorly. Furca base and branches covered with three-lobed, spined scales and oblong, keeled scales. Molecular diagnosis 18 S rRNA gene: 672 T, 1072 ‒. ITS 2: 26 G, 28 A, 40 G, 41 T, 53 G, 60 C, 62 T, 84 A, 96 A, 107 ‒, 117 T, 131 A, 132 A, 133 A, 136 ‒, 137 ‒, 139 C, 156 G, 157 T, 159 T, 168 A, 173 ‒. 28 S rRNA gene: 530 G, 608 C, 687 A, 690 G, 717 A, 719 C, 756 C. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 23 (67 ‒ 69) ATT, 28 (82 ‒ 84) CTT, 44 (130 ‒ 132) GTC, 45 (133 ‒ 135) GTA, 63 (187 ‒ 189) GGA, 72 (214 ‒ 216) CTT, 82 (244 ‒ 246) CCA, 97 (289 ‒ 291) AGT, 98 (292 ‒ 294) TTA, 100 (298 ‒ 300) CTT, 103 (307 ‒ 309) GCG, 129 (385 ‒ 387) AGG, 142 (424 ‒ 426) GCA, 146 (436 ‒ 438) TTG, 155 (463 ‒ 465) ACC, 156 (466 ‒ 468) CTA, 162 (484 ‒ 486) GGT, 165 (493 ‒ 495) TTT, 167 (499 ‒ 501) CGT, 170 (508 ‒ 510) TTA, 179 (535 ‒ 537) GTT, 184 (550 ‒ 552) CTG, 190 (568 ‒ 570) GCC, 212 (634 ‒ 636) GGA, 221 (661 ‒ 663) CTA. Reference molecules are shown in Figures 5, 7, and Supp. file 1: Fig. S 9 A. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p- distance from species described in the present study is 0.22 ‒ 4.06 % in 18 S, 18.19 ‒ 34.22 % in ITS 2, 2.23 ‒ 7.12 % in 28 S, and 11.37 ‒ 13.15 % in COI. There are 2 ‒ 13 CBCs (except for Ch. (H). superbus sp. nov., where there are no CBCs) in the 18 S rRNA molecule, 2 ‒ 4 CBCs in the ITS 2 molecule, and 1 ‒ 12 CBCs in the first two domains of the 28 S rRNA molecule.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFBCFFA5509ADE7A2AE9FCBD.taxon	etymology	Etymology The Latin adjective ‘ mirabil · is, - is, - e ’ [m, f, n] (‘ marvelous, extraordinary’) refers to the extraordinary long dorsal spines.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFBCFFA5509ADE7A2AE9FCBD.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (photomicrographs, hologenophore); Greenhouse pond, Botanical Garden, Karlova Ves, Bratislava, Podunajská rovina plain (type locality); 48 ° 08 ′ 46.8 ″ N, 17 ° 04 ′ 22.6 ″ E; CU-FNS- 11 - 09 - 19 / HO. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The holotype is shown in Fig. 12. Paratypes SLOVAKIA • 2 adults (photomicrographs); same collection data as for holotype; CU-FNS- 25 - 10 - 19 / PA- 1, CU-FNS- 02 - 10 - 19 / PA- 2. Photomicrographs of paratype specimens are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. Paratypes are shown in Figs 13 – 14. Type material A DNA sample of the holotype specimen BZs 02 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427888). Type locality Greenhouse pond, Botanical Garden of Comenius University, Karlova Ves, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 08 ′ 46.8 ″ N, 17 ° 04 ′ 22.6 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen BZs 02 have been deposited in GenBank under the following accession numbers: OM 421704, OM 421680, and OM 424059, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFBCFFA5509ADE7A2AE9FCBD.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) mirabilis sp. nov. is about 83 – 107 µm long and has a slender body that is tenpin-shaped, with a clearly defined head region, a narrowing neck, and a slightly bulbous trunk (Figs 10 A – B, G, 12 A – C). Body width is 10 – 19 µm at U 10, 11.2 – 11.6 µm at U 50, and 17.5 – 18.5 µm at U 60. The head is relatively wide, with a plate-like, rounded cephalion. The neck (ca U 12 – U 27) is clearly demarcated and smoothly continues to the trunk region, i. e., a distinct neck constriction is formed. The trunk is nearly as wide as the head, gradually dilating from about U 39 to U 62 where it reaches the maximum width. Then it gradually tapers towards U 84 where vaulted margins of the furca branches start to form. Dorsal sensory bristles (setolae) arise from the cuticle in two pairs at U 25 and U 75 (Figs 14 A, 16 C). The furcal indentation is broadly U-shaped. The furca branches are set apart and diverge posteriorly. Well-developed adhesive tubes are 9.4 – 10.5 µm long, they are straight and narrow (Fig. 17 G). HEAD. The head is roughly five-lobed. The cephalion (U 1 – U 2) is rounded, 0.4 – 0.9 µm wide, clearly demarcated in the body outline, appears as a lens in the ventral view, and has a free posterior (dorsal) edge (Figs 10 A – B, F, 12 B, 13 A – C). The epipleurae are approximately at U 3 – U 5 and the hypopleurae are at ca U 6 – U 9. Notches separating the epipleurae from the hypopleurae are very shallow, causing that they are only inconspicuously marked in the head outline (Fig. 13 A, E). Two pairs of cephalic ciliary tufts emerge laterally between the cephalion and the epipleurae edge (ca U 3) as well as between the epi- and the hypopleurae edge (U 5) (Figs 10 A, F – G, 12 A ‒ C, 13 A, E). The hypostomium is absent and the under-mouth area carries only ciliary patches. Each field is composed of several irregular groups of basal bodies (kinetosomes). The mouth ring is oval, 5.0 – 5.5 µm in the largest diameter, located subterminally at U 2 – U 4. There are strong but short, rod-like reinforcements lining the walls of the mouth ring as well as an inner pair of cuticular teeth located in the center of the mouth opening (Figs 10 C, 13 D). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 30, is 26 – 30 µm long and 5.3 – 7.8 µm wide, sinuous, and has marked anterior and posterior dilatations (Figs 10 F, 13 A, C, white arrowheads). The posterior dilatation (ca U 20 – U 30) is larger than the anterior one (ca U 5 – U 8) (Supp. file 1: Table S 2). The pharynx is connected to the straight intestine through a pharyngeal ‒ intestinal junction (Fig. 13 B). The intestine runs from U 31 to U 84 and has a separate, well-differentiated anterior section (U 31 – U 33) (Figs 10 F, 13 A). There are highly refractive and regularly arranged structures well recognizable in the lateral view of the intestine (Figs 13 F, 14 G, double white arrowheads). Transversal bands connected to the base of dorsal scales are recognizable from ca U 10 (Figs 10 F, 13 A). The adhesive gland (ca U 85 – U 91) is placed right behind the terminal part of the intestine, it is broadly pyriform forming a short dichotomy at the subtle furca base (Figs 10 F, 13 G). SCALES. Almost the entire body is covered by not overlapping three-lobed scales that adhere to the basal cuticle layer along their whole perimeter. Scales are distributed in a minimum of 10 – 12 longitudinal rows, with 17 scales in the central row. Central dorsal and dorsolateral longitudinal rows of scales begin at the level of the anterior edge of the hypopleurae (ca U 6), lateral rows start at their posterior end (ca U 9). Ventral and ventrolateral rows are hardly visible due to the highly pronounced dorsal spines (for further explanation, see below). Head scales (ca U 6 – U 25) are fairly small, i. e., 3.3 – 4.1 × 1.9 – 3.9 µm in size. Two types could be recognized: (i) lateral boomerang-shaped scales with a subtle anterior lobe, the transition between anterior and posterior lobes is indistinct and continuous, α = 170 – 177 °, and β = 70 – 85 ° (Fig. 11 A) and (ii) dorsal / dorsolateral scales with a distinctly elongated anterior lobe and a smaller angle α ranging from 146 to 169 °, angle β spans a wide range of 68 – 108 °, and the transition between anterior and posterior lobes is marked (Figs 11 B, 14 B). Neck dorsal scales are 3.2 – 5.1 × 2.0 – 2.7 µm in size. They are anteriorly more broadly rounded, their angle α is slightly smaller (153 – 163 °), β is closer to the right angle (82 – 91 °) than in head scales, and the transition between anterior and posterior lobes is marked (Figs 11 C, 14 A). This type of scale terminates right at the anterior border of the trunk region (ca U 26 – U 39). The trunk region is covered by four types of scales: (i) lateral scales (U 37 – U 50) with a tongue-shaped anterior lobe and comparatively narrow posterior lobes, α = 149 – 150 °, and β = 76 – 82 °, the transition between anterior and posterior lobes is indistinct and continuous (Figs 11 D, 14 F); (ii) dorsolateral scales (U 50 – U 81) with a tongue-shaped anterior lobe and wider posterior lobes being closer together, α = 147 – 158 °, β = 68 – 76 °, the transition between anterior and posterior lobes is indistinct (Figs 11 E, 14 A, C); (iii) dorsal big scales (U 50 – U 78) with a tapered, triangular anterior lobe and narrowly rounded posterior lobes, α = 175 – 179 °, β = 57 – 68 °, the transition between anterior and posterior lobes is also indistinct (Figs 11 F, 14 A); and (iv) dorsal smaller scales (U 80 – U 90) with an anteriorly rounded anterior lobe, the transition between anterior and posterior lobes is marked (Figs 11 G, 14 D). SPINES. All spines bear a lateral denticle and gradually narrow towards the distal end. Three main types could be distinguished. The most common type of spines emerges from the head (2.7 – 3.7 µm long), neck (4.5 – 7.1 µm long), trunk dorsolateral (4.0 – 6.8 µm long), and lateral scales (6.8 – 8.8 µm long). The lateral denticle is minute and its tip is distant only 0.7 – 0.9 µm from the spine apex, which corresponds to a d - ratio of 25.3 – 31.2 %. Lateral spines are, however, slightly thinner (0.32 – 0.35 µm vs 0.30 – 0.43 µm) and their subterminal denticle is rather inconspicuous and much closer to the spine apex (d - ratio 8 – 10 %) in comparison with head, neck, and dorsolateral spines. The second type is represented by the prominent, elongated spines carrying a conspicuous denticle (2.6 – 5.6 µm long) associated with a membrane (Figs 10 D, 11 F, 12 B – C, 13 F, 14 A, G). The denticle is 6.4 – 7.9 µm distant from the spine apex, which corresponds to a d - ratio of 18.2 – 22.6 %. Type 2 spines are 20.7 – 35.9 µm long and comparatively wide (1.8 – 1.9 µm) at the base. Altogether only five horizontal rows of dorsal scales are equipped with this type of spines (U 50 – U 78). The last type could be found only on the two terminal rows of dorsal scales on the furca base and branches. These spines are significantly shorter (13.0 – 18.4 µm vs 20.7 – 35.9 µm) and thinner (0.7 – 0.8 µm vs 1.1 – 1.6 µm) than the previous type. They are slightly curved and hair-like tapered distally. Although their denticle is well recognizable, it is not associated with a distinct membrane. The d - value is 2.9 – 4.4 µm and the d - ratio is 22.0 – 25.7 % (Figs 10 E, 11 G, 14 D). VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Unfortunately, the ventral side could not be observed in detail due to the very long and strong type 2 spines that precluded turning over and squeezing the worms. Despite that, the following observations could be done. The longitudinal ciliary bands begin at ca U 7 and run backward to ca U 87. They are somewhat wider on the neck than on the trunk where they narrow slightly from ca U 78. The ciliary bands are accompanied by a ventrolateral row of small (2.4 – 3.0 × 1.0 – 1.5 µm in size), oblong, and keeled scales that start at U 7. The upper furcal region (U 84 – U 90) carries two types of scales: (i) three-lobed, spined scales with a broadly rounded anterior lobe, narrowly rounded posterior lobes, α = 137 – 171 °, and β = 59 – 72 ° (Figs 10 G, 11 H) and (ii) oblong and keeled scales being 1.5 – 3.9 × 0.7 – 1.5 µm in size (Figs 10 G, 11 I).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFB4FFA0509BDE0C2AFBF830.taxon	description	urn: lsid: zoobank. org: act: 781619 BA- 32 C 2 - 4336 - A 729 - 2 BDA 3 E 13 C 7 D 4 Figs 15 ‒ 17; Supp. file 1: Table S 3	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFB4FFA0509BDE0C2AFBF830.taxon	diagnosis	Morphological diagnosis Body stocky and about 107 µm long. Head wider than neck, separated from trunk by an inconspicuous neck constriction. Cephalion, epipleurae, and hypopleurae clearly demarcated. Trunk gradually widens from ca U 37 to U 60 and then gradually tapers towards furca base at U 80. Mouth ventral, with delicate protruding structures, no cuticular teeth. Pharynx without dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, not overlapping, distributed in 10 – 12 columns, 15 scales per column. Spines with a short lateral denticle. Scales and spines increase gradually in size in a posterior direction. Dorsal surface covered by scales from posterior end of cephalion (ca U 3) to furca base (ca U 93). Furca base short, lateral margins of furca branches more or less straight, furcal indentation deeply U-shaped, adhesive tubes well-developed, almost parallel. Furca base and branches covered with oval, keeled scales. Molecular diagnosis 18 S rRNA gene: 341 C. ITS 2: 26 T, 28 G, 40 A, 41 C, 50 T, 62 G, 78 C, 87 A, 96 C, 107 A, 108 A, 112 ‒, 116 G, 117 A, 118 A, 131 T, 139 T, 157 C, 167 T, 168 T. 28 S rRNA gene: 317 A, 690 T, 797 T, 902 G. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 29 (85 ‒ 87) AGT, 44 (130 ‒ 132) GTA, 71 (211 ‒ 213) CCA, 75 (223 ‒ 225) GGT, 81 (241 ‒ 243) TTT, 97 (289 ‒ 291) TCT, 124 (370 ‒ 372) GCT, 126 (376 ‒ 378) GCC, 139 (415 ‒ 417) CTA, 142 (424 ‒ 426) GCC, 155 (463 ‒ 465) ACT, 170 (508 ‒ 510) CTG, 189 (565 ‒ 567) TTC, 196 (586 ‒ 588) CTG, 221 (661 ‒ 663) CTG. Reference molecules are shown in Supp. file 1: Figs S 1, S 9 B, S 13. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.22 ‒ 4.00 % in 18 S, 18.19 ‒ 34.76 % in ITS 2, 2.23 ‒ 6.70 % in 28 S, and 9.04 ‒ 13.44 % in COI. There are 2 ‒ 13 CBCs (except for Ch. (H). mirabilis sp. nov., where there are no CBCs) in the 18 S rRNA molecule, 3 ‒ 4 CBCs in the ITS 2 molecule, and 1 ‒ 11 CBCs in the first two domains of the 28 S rRNA molecule.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFB4FFA0509BDE0C2AFBF830.taxon	etymology	Etymology The Latin adjective ‘ superb · us, - a, - um ’ [m, f, n] (‘ proud’) refers to the ‘ beautiful appearance’ of the new species.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFB4FFA0509BDE0C2AFBF830.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (photomicrographs, hologenophore); Zlaté Piesky lake, municipal recreation area, Ružinov, Bratislava, Podunajská rovina plain; 48 ° 11 ′ 17.1 ″ N, 17 ° 11 ′ 24.3 ″ E; CU-FNS- 22 - 06 - 20 / PA. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The holotype is shown in Figs 16 A, 17 C – G. Paratype SLOVAKIA • adult (photomicrographs, hologenophore); Kuchajda lake, municipal recreation area, Nové Mesto, Bratislava, Podunajská rovina plain (type locality); 48 ° 10 ′ 15.7 ″ N, 17 ° 08 ′ 30.6 ″ E; CU- FNS- 15 - 06 - 20 / HO. Photomicrographs of the paratype specimen are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The paratype is shown in Figs 16 B, 17 A – B. Type material A DNA sample of the holotype specimen ZPvs 55 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427126). Type locality Zlaté Piesky lake, Ružinov, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 11 ′ 17.1 ″ N, 17 ° 11 ′ 24.3 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen ZPvs 55 have been deposited in GenBank under the following accession numbers: OM 421708, OM 421684, and OM 424063, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFB4FFA0509BDE0C2AFBF830.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) superbus sp. nov. is about 107 µm long and has a stocky body that is tenpin-shaped, with a clearly defined head region, a narrowing neck, and a rather bulbous trunk (Figs 15 A, H, 16 A). Body height in lateral view is 14.0 – 15.0 µm at U 10, 15.0 – 15.4 µm at U 50, and 16.1 – 17.0 µm at U 60. The head is relatively wide, with a plate-like, rounded cephalion. The neck (ca U 12 – U 27) smoothly continues to the trunk, which is significantly wider than the head, gradually dilates from about U 37 to U 60 where it reaches the maximum width. Then it gradually tapers towards U 80 where curved margins of the furca branches begin to emerge. Dorsal sensory bristles arise from the cuticle in two pairs at U 12 and U 79 (Fig. 19 A). The furcal indentation is deeply U-shaped. The furca branches are set apart and diverge posteriorly. Well-developed adhesive tubes are approximately 9 µm long, more or less straight, and run almost in parallel (Figs 15 A, H, J, 16 A). HEAD. The head is five-lobed. The cephalion (U 1 – U 2) is rounded, clearly demarcated in the body outline, appears as a lens in the ventral view, and has a free posterior (dorsal) edge (Figs 15 A, H, J – K, 16 B, 17 C). The epipleurae are formed approximately at U 3 – U 5 while the hypopleurae at ca U 6 – U 13. The latter structures are well recognizable in the head outline (Figs 15 A – B, 16 A, black stars). Two pairs of cephalic ciliary tufts emerge laterally between the cephalion and the epipleurae edge (ca U 3) as well as between the epi- and the hypopleurae edge (U 6) (Figs 15 A, H, 16 A). The hypostomium (ca U 4 – U 6) is free of structures, lined only with ciliary patches. The mouth ring is oval, 4.4 – 4.9 µm in the largest diameter, located subterminally at U 3 – U 6. There are strong, rod-like reinforcements lining the mouth walls and delicate structures protruding from the mouth ring (Figs 15 H, K, 17 C). Inner cuticular teeth are not present. INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 34, is 28 – 32 µm long and 5.9 – 8.3 µm wide, sinuous, and has no dilatations (Figs 15 J, 16 B, 17 C). The cerebral ganglion appears as a mass surrounding the pharynx along its whole length (Fig. 15 K). The salivary glands are recognizable as small hyaline balls situated at the dorsal side of the pharynx around at U 33 (Figs 15 J, 16 B, 17 A). The intestine runs from U 35 to U 82 and has a separate, well-differentiated anterior section (U 35 – U 38) (Figs 15 J, 16 B). Transversal bands connected to the base of dorsal scales are well recognizable under DIC and secondary magnification of 2500 × (Figs 15 J, 16 B, 17 A – B). The adhesive gland (ca U 85 – U 91) is placed right behind the terminal part of the intestine, forming a short dichotomy at the subtle furca base. SCALES. Almost the entire body is covered by not overlapping three-lobed scales that adhere to the basal cuticle layer along their whole perimeter. Scales are distributed in a minimum of 12 longitudinal rows, with 10 scales in the central row. Their size increases gradually in a posterior direction. Central dorsal and dorsolateral longitudinal rows of scales begin at the level of the anterior edge of the epipleurae (ca U 5), while lateral rows start at the posterior end of the hypopleurae (ca U 13). Ventral rows are hardly visible due to the thick, elongated dorsal spines (for further explanation, see below) and long locomotory cilia. Three main types of scales could be recognized with respect to the shape of the anterior lobe of scales: (i) head and upper-neck scales (U 5 – U 28) with a small, rounded anterior lobe and elongated posterior lobes, α = 160 – 170 °, and β = 89 – 98 ° (Figs 15 B, 17 E), (ii) lower-neck and anterior trunk scales (U 29 – 42) with a truncated anterior lobe and elongated posterior lobes, α = 160 – 175 °, and β = 76 – 93 ° (Figs 15 C, 17 D), and (iii) posterior trunk scales (U 45 – 80) with a more broadly rounded anterior lobe and a larger angle β (101 ‒ 110 °) formed by the posterior lobes (Figs 15 D, 17 G). The transition between anterior and posterior lobes is indistinct and continuous in all scales. SPINES. All spines bear a distinct lateral denticle and gradually narrow towards their distal end. Keels start near the anterior margin of scales. Spines are not straight but distinctly curved (Figs 15 A, G ‒ J, 16 A – B, 17 D ‒ G). They do not differentiate into various types, only their length changes in a posterior direction (Supp. file 1: Table S 3). The most pronounced change occurs at the beginning of the trunk (Figs 15 H, 16 A), where dorsal spines increase significantly from 6.7 – 10.7 µm to 10.8 – 13.0 µm. The lateral denticle is comparatively distant from the spine apex, i. e., d - value ranges from 1.7 ‒ 5.1 μm, which corresponds to a d ratio of 21.4 ‒ 34.7 %. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Unfortunately, the ventral side could not be observed in detail due to the thickness of the dorsal spines that precluded turning over and squeezing the worms. Moreover, the ventral locomotory cilia also hampered detailed observations of the ventral side. Despite these problems, the following observations could be done. The longitudinal ciliary bands begin at ca U 10 and run backward to ca U 85. The ciliary bands are accompanied by two ventrolateral rows of small (2.0 – 2.9 × 1.9 – 2.2 µm in size), three-lobed scales that start at U 13. The interciliary field bears small (1.7 – 2.6 × 0.9 – 1.2 µm in size), oval scales without spines or keels (Fig. 15 E). The upper furcal region (U 84 – U 90) carries two types of scales: (i) lateral three-lobed, spined scales with a broadly rounded anterior lobe, narrowly rounded posterior lobes, α = ~ 140 °, and β = ~ 73 ° and (ii) oblong and keeled scales being 0.84 – 1.2 × 1.47 – 1.72 µm in size (Fig. 15 F).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF8EFF975098DC3628FFFEF1.taxon	description	urn: lsid: zoobank. org: act: 0 B 0 D 89 B 0 - 6 D 24 - 4 D 99 - A 359 - 18 C 41 CFA 1 BCE Figs 18 ‒ 22; Supp. file 1: Table S 4	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF8EFF975098DC3628FFFEF1.taxon	diagnosis	Morphological diagnosis Body elongated and about 108 ‒ 143 µm long. Head slightly wider than neck, separated from trunk by an inconspicuous neck constriction. Cephalion clearly demarcated, epipleurae and hypopleurae not recognizable. Trunk comparatively narrow, not broader than head, widest at ca U 63, narrowest at ca U 88. Mouth ventral, no cuticular teeth. Hypostomium bears a rectangular cuticular structure accompanied by two posterior lateral lamellae. Pharynx with anterior and posterior dilatations. Intestine straight, with a marked anterior section. Scales slightly overlapping, distributed in 16 – 18 columns, 40 – 45 scales per column. Dorsal surface covered from posterior end of cephalion (ca U 1) to furca base (U 94) with (i) spined, three-lobed scales with rounded anterior end and (ii) spined, three-lobed scales with truncated anterior end. Spines short, narrowed posteriorly, without denticles. Ventral side carries two broad ciliary bands and two pairs of ciliary fields around mouth and hypostomium. Interciliary filed bears (i) V-shaped scales without keels, (ii) bowl-shaped scales without keels, (iii) obtriangular scales with very minute keels, and (iv) narrowly obovate, keeled scales. Furca base longer than adhesive tubes, lateral margins more or less straight, furcal indentation deeply V-shaped, adhesive tubes diverging posteriorly. Dorsal side of furca base and branches covered with three-lobed scales, ventral side with oblong, spined scales and oval to broadly fusiform, keeled scales. Molecular diagnosis 18 S rRNA gene: 78 C, 148 T, 223 A, 225 A, 228 T, 235 A, 239 T, 240 T, 243 A, 264 A, 267 ‒, 282 T, 283 T, 286 A, 288 A, 336 T, 337 T, 338 C, 340 C, 345 A, 546 A, 639 A, 648 T, 649 A, 652 C, 656 T, 658 A, 664 T, 666 T, 676 A, 678 A, 681 T, 686 T, 688 A, 694 T, 714 T, 722 T, 733 A, 741 A, 1059 A, 1060 A, 1082 T, 1083 T, 1366 A, 1368 T, 1372 G, 1373 A, 1374 A, 1376 T, 1377 T, 1381 ‒, 1383 C, 1384 ‒, 1388 A, 1391 T, 1507 A, 1526 T, 1535 A, 1690 T, 1724 T, 1732 C, 1736 T. 28 S rRNA gene: 275 A, 292 A, 309 T, 480 T, 485 T, 487 A, 489 ‒, 500 A, 504 A, 506 A, 520 C, 522 T, 543 A, 588 C, 589 C, 591 ‒, 599 T, 603 T, 608 A, 615 A, 628 C, 634 T, 645 A, 648 T, 652 T, 657 T, 661 A, 662 A, 688 T, 690 A, 698 A, 704 T, 706 A, 713 T, 722 A, 735 G, 742 T, 746 T, 764 A, 777 A, 784 T, 789 C, 791 A, 795 A, 798 A, 810 A, 813 T, 814 A, 819 A, 965 A, 966 C, 996 C. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 20 (58 ‒ 60) CTA, 32 (94 ‒ 96) AGT, 45 (133 ‒ 135) GTC, 49 (145 ‒ 147) GCT, 51 (151 ‒ 153) GTC, 55 (163 ‒ 165) TTC, 57 (169 ‒ 171) GTT, 69 (205 ‒ 207) CTA, 76 (226 ‒ 228) GCG, 77 (229 ‒ 231) CCA, 91 (271 ‒ 273) TTA, 101 (301 ‒ 303) GTG, 109 (325 ‒ 327) GCC, 111 (331 ‒ 333) ACA, 114 (340 ‒ 342) ACG, 133 (397 ‒ 399) GCT, 154 (460 ‒ 462) ACC, 156 (466 ‒ 468) TTA, 184 (550 ‒ 552) TTG, 186 (556 ‒ 558) TTA, 205 (613 ‒ 615) AGG. Reference molecules are shown in Supp. file 1: Figs S 2 and S 14. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 4.00 ‒ 4.39 % in 18 S, 6.78 ‒ 9.79 % in 28 S, and 10.96 ‒ 13.59 % in COI. There are 13 ‒ 16 CBCs in the 18 S rRNA gene and 11 ‒ 18 CBCs in the 28 S rRNA gene.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF8EFF975098DC3628FFFEF1.taxon	etymology	Etymology The Latin adjective ‘ optabil · is, - is, - e ’ [m, f, n] (‘ desirable’) refers to the very elegant appearance of the new species.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF8EFF975098DC3628FFFEF1.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (photomicrographs, hologenophore); temporary pond in the floodplain area of the River Morava, Devín, Bratislava, Podunajská rovina plain; 48 ° 10 ′ 29.4 ″ N, 16 ° 58 ′ 35.8 ″ E; CU- FNS- 05 - 03 - 20 - 1 / HO. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The holotype is shown in Figs 20 B – C, 21 C, 22 B – C. Paratypes SLOVAKIA • 2 adults (photomicrographs, both hologenophores); same collection data as for holotype; CU-FNS- 05 - 03 - 20 - 2 / PA- 1, CU-FNS- 05 - 03 - 20 - 3 / PA- 2. Photomicrographs of paratype specimens are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. Paratypes are shown in Figs 20 A, 21 A – B, D, 22. Type material A DNA sample of the holotype specimen DB 34 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427607). Type locality Ephemeral pond in the floodplain area of the River Morava near the foothill of the Devín castle, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 10 ′ 29.4 ″ N, 16 ° 58 ′ 35.8 ″ E. Gene sequences The nuclear 18 S and 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen DB 34 have been deposited in GenBank under the following accession numbers: OM 421710, OM 421686, and OM 424065, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF8EFF975098DC3628FFFEF1.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) optabilis sp. nov. is about 108 – 143 µm long and has a slender elongated body, with a head region slightly broader than the inconspicuous neck and a more or less bulbous trunk (Figs 18 A, 19 A, E, 20 A). Body width is 18.8 – 21.7 µm at U 10, 22.5 – 23.7 µm at U 50, and 26.1 – 30.7 µm at U 60. The head is relatively wide (11 – 15 µm at U 6), with a plate-like, rounded cephalion. Epi- and hypopleurae are not recognizable. The neck (ca U 12 – U 25) is only inconspicuously marked and smoothly continues to the trunk region. The trunk is about as narrow as the head, gradually dilating from approximately U 38 to U 63, where it reaches the maximum width. Then it gradually tapers towards U 88, where the curved margins of the furca branches start to form. Dorsal sensory bristles were not observed. The furcal indentation is deeply V-shaped. The furca branches are set apart and diverge posteriorly. Well-developed adhesive tubes are approximately 9 µm long, they are straight and almost in parallel (Figs 18 A, 19 A, D – E, 21 D, 22 E). HEAD. The cephalion (U 1) is rounded, clearly demarcated in the body outline, appears as a lens in the ventral view (Figs 19 A, E, 21 A). Pairs of cephalic ciliary tufts emerge laterally at U 4 and U 6 (Figs 19 A, E, 21 A). The mouth ring is oval, 5.2 – 6.2 µm in the largest diameter, and is located subterminally at U 2 – U 5. There are strong but short, rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring. Inner cuticular teeth are not present (Figs 20 A, 21 B). The hypostomium (ca U 5 – U 9) has a complex morphology, i. e., bears a rectangular plate (5.0 × 2.9 µm) with a small central protuberance and two lamellae situated posterior to the plate. The lateral sides of the hypostomium are lined by a relatively wide pair of sensoric ciliary patches from U 3 to U 8 (Figs 19 A, 20 A, 21 B). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 29, is 28.0 – 33.4 µm long and 7.3 – 7.8 µm wide, sinuous, and has marked anterior and posterior dilatations (Fig. 19 E). The posterior dilatation (ca U 20 – U 25) is larger than the anterior one (ca U 7 – U 9) (Supp. file 1: Table S 4). The intestine runs from U 29 to U 85 and has a separate, well-differentiated anterior section (U 29 – U 33). Transversal bands connected to the base of dorsal scales are well recognizable (Fig. 19 E). The adhesive gland (ca U 85 – U 87) is placed right behind the terminal part of the intestine forming a short dichotomy at the subtle furca base. The organ X has a lemniscate shape and is situated ahead of adhesive glands (Figs 19 E, 21 D). SCALES. Almost the entire body is covered by slightly overlapping three-lobed scales that adhere to the basal cuticle layer along either all or most of their perimeter. Scales are distributed in 16 – 18 longitudinal rows, with 40 – 45 scales in the central row. Their size increases slightly in a posterior direction. Central dorsal and dorsolateral longitudinal rows of scales begin at the level of the anterior edge of the cephalion (ca U 1), while lateral rows start at ca U 6. They run almost along the whole body length (till U 94). Ventrolateral rows commence at U 23 due to the highly developed and wide anterior part of ciliary rows and terminate in the furcal region (at ca U 91). Ventral rows start at U 10, are staggered, and exhibit a horizontal zonation pattern. Given the shape of the anterior scale lobe, two main types were recognized: (i) head and neck scales (U 1 – U 30), with a rounded anterior lobe and comparatively short posterior lobes, α = 180 – 196 °, β = 47 – 68 ° (Figs 18 B, D, 20 B, 22 C) and (ii) trunk and dorsal furca scales (U 31 – U 93), with a truncated anterior lobe and longer posterior lobes, α = 162 – 188 °, β = 58 – 85 ° (Figs 18 C, E, 22 B). Both types share an indistinct and continuous transition between the anterior and posterior lobes. Rounded structures (1.0 – 2.4 µm across) irregularly interspersed within type 1 and 2 scales were observed along the whole dorsal side (Figs 18 A – C, 20 B – C). As they were clearly recognizable only in a single specimen, we cannot exclude that these structures are artifacts. The V-shaped furcal indentation carries the fourth type of dorsal scales that are three-lobed and have a tongue-shaped anterior lobe, relatively narrow posterior lobes, α = 156 – 176 °, β = 56 – 80 °, and a marked transition between the anterior and posterior lobes (Fig. 18 G). SPINES. Dorsal, dorsolateral, lateral, and ventrolateral scales bear simple, slightly curved spines that gradually narrow towards the distal end (Figs 18 D – G, 20 A). The spine emerges rather close to the anterior margin of scales. Spines do not differentiate into various types, only their length slightly increases in a posterior direction (Supp. file 1: Table S 4). A lateral denticle is not formed. Ventral scales are spineless. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Ciliary bands start at U 10, where they are conspicuously broad (Figs 19 A, 21 B, asterisks). However, they begin to narrow from U 25 and terminate at U 88. The ciliary bands are accompanied by two ventrolateral rows of three-lobed scales that extend from U 22 to U 91. They are 3.6 – 4.9 × 2.6 – 3.6 µm in size and have an indistinct and continuous transition between the anterior and posterior lobes (Fig. 19 A). The ventral interciliary field bears four types of horizontally distributed scales: (i) minute (0.7 – 0.9 × 0.8 – 1.2 µm), V-shaped, double-edged scales without keels (U 10 – U 30) (Fig. 19 B); (ii) minute (0.8 – 1.1 × 0.8 – 1.3 µm), bowl-shaped, double-edged scales without keels (U 31 – U 36) (Fig. 19 C); (iii) small (1.3 – 2.0 × 1.0 – 1.5 µm), obtriangular, doubleedged scales with a minute keel (U 38 – U 81) (Figs 19 D, 22 A); and (iv) larger (1.7 – 3.4 × 1.0 – 1.5 µm), narrowly ovate, double-edged, keeled, and slightly overlapping scales arranged in three distinct rows (U 82 – U 88) (Fig. 19 D, F). The furcal region (U 87 – U 93) carries two types of scales: (i) a pair of oblong, comparatively large (7.3 – 7.6 × 2.4 – 2.6 µm), spined scales, with a broadly rounded posterior end (Figs 19 D, H, 22 F) and (ii) oval to broadly fusiform, rather small (1.0 – 4.1 × 1.0 – 1.8 µm), keeled scales (Figs 19 D, G, 22 E).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF86FF8F50A5DC532BD5FD2B.taxon	description	urn: lsid: zoobank. org: act: 7 B 146 EA 8 - 7 E 66 - 46 A 3 - A 4 C 2 - 8707 A 9 C 9 EB 56 Figs 23 ‒ 27; Supp. file 1: Table S 5	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF86FF8F50A5DC532BD5FD2B.taxon	diagnosis	Morphological diagnosis Body elongated and about 130 µm long. Head slightly wider than neck, separated from trunk by an inconspicuous neck constriction. Cephalion, epipleurae, and hypopleurae clearly demarcated. Trunk comparatively narrow, not broader than head, widest at ca U 62, narrowest at ca U 87. Mouth ventral, three cuticular teeth. Hypostomium bears a pentagonal cuticular structure with two protuberances. Pharynx without dilatations. Intestine straight, with a marked anterior section. Scales slightly overlapping, distributed in 14 columns, 30 – 32 scales per column. Dorsal surface covered with: (i) head scales small, with a subtle, well-delimited anterior lobe and comparatively long and diverging posterior lobes; (ii) neck scales boomerang-like, with a broadly rounded anterior lobe, elongated posterior lobes; (iii) dorsolateral neck scales with a well-delimited, broadly rounded anterior lobe and distinct transition between anterior and posterior lobes; (iv) main trunk scales with a rounded anterior end, posterior lobes comparatively long, narrowly rounded distally, and diverging; (v) posterior trunk scales with a conspicuously prolonged, tongue-shaped anterior lobe and relatively short posterior lobes tapering distally; and (vi) furca base scales with a narrower and more elongated anterior lobe and short posterior lobes very narrowly rounded or almost acute distally. Spines slightly increasing in length from head to posterior trunk region, gradually tapering to become hair-like terminally, without denticles. Ventrolateral spines shorter than dorsal ones. Ventral side carries two broad, anteriorly connected (U 9 – U 27) ciliary bands. Interciliary field covered by (i) minute, tongue-like, keeled scales; (ii) small, roughly rectangular, keeled scales; (iii) oblong scales with a short spine; and (iv) a pair of big, elongated oval, keeled scales. Furca branches slightly longer than adhesive tubes, lateral margins more or less straight, furcal indentation deeply V-shaped, adhesive tubes short. Dorsal side of furca branches covered with elongated oval, keeled scales and ventral side of furca branches covered with (i) two pairs of three-lobed, spined scales, having an elongated, tongue-shaped anterior lobe and comparatively short, narrowly rounded to acute posterior lobes and (ii) cordiform, short-spined scales. Molecular diagnosis 18 S rRNA gene: 268 A, 1739 G. 28 S rRNA gene: 128 C, 136 G, 447 G, 691 A, 737 C, 764 T, 765 A, 767 A. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 84 (250 ‒ 252) CTA, 91 (271 ‒ 273) CTA, 99 (295 ‒ 297) CTA, 102 (304 ‒ 306) TCG, 120 (358 ‒ 360) TCC, 154 (460 ‒ 462) ACT, 192 (574 ‒ 576) GGA, 213 (637 ‒ 639) GGG. Reference molecules are shown in Supp. file 1: Figs S 3 and S 15. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.38 ‒ 4.17 % in 18 S, 2.49 ‒ 9.44 % in 28 S, and 8.44 ‒ 13.15 % in COI. There are 1 ‒ 14 CBCs in the 18 S rRNA molecule and 2 ‒ 18 CBCs in the first two domains of the 28 S rRNA molecule.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF86FF8F50A5DC532BD5FD2B.taxon	etymology	Etymology The Latin adjective ‘ avar · us, - a, - um ’ [m, f, n] (‘ avaricious, covetous, greedy’) refers to the three cuticular teeth of the new species.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF86FF8F50A5DC532BD5FD2B.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (the specimen was destroyed during DNA extraction); Vajspeterský potok creek, Rača, Bratislava, Podunajská rovina plain; 48 ° 12 ′ 12.8 ″ N, 17 ° 07 ′ 46.9 ″ E. Paratypes SLOVAKIA • 2 adults (photomicrographs); same collection data as for holotype; CU-FNS- 25 - 02 - 20 / PA- 1, CU-FNS- 26 - 02 - 20 / PA- 2. Photomicrographs of paratype specimens are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. Paratypes are shown in Figs 25 – 27. Type material A DNA sample of the holotype specimen VP 32 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427566). Type locality Vajspeterský potok creek, Rača, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 12 ′ 12.8 ″ N, 17 ° 07 ′ 46.9 ″ E. Gene sequences The nuclear 18 S and 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen VP 32 have been deposited in GenBank under the following accession numbers: OM 421713, OM 421689, and OM 424068, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF86FF8F50A5DC532BD5FD2B.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) avarus sp. nov. is about 130 µm long and has a slender elongated body, with a head region slightly broader than the neck and trunk (Figs 23 A, K, 24 A, 25 A ‒ C). Body width is 22.0 – 23.0 µm at U 10, 18.0 – 19.0 µm at U 50, and 20.0 – 21.0 µm at U 60. The head is relatively wide (11 – 15 µm at U 6), with a plate-like cephalion. Epi- and hypopleurae are clearly demarcated in the head outline (Figs 23 A, K, 24 A, 25 A ‒ C, 26 A). The neck (ca U 14 – U 27) is only inconspicuously marked and smoothly continues to the trunk. In comparison with the head, the trunk is comparatively slender, gradually dilatating from about U 35 to U 55, where it reaches the maximum width. Then, the trunk gradually narrows towards U 87, where more or less straight margins of the furca branches start to form. Dorsal sensory bristles arise from the cuticle in two pairs at U 28 and U 78 (Fig. 23 A, L). The furcal indentation is deeply V-shaped. Well-developed adhesive tubes are approximately 6 – 12 µm long, they are straight and short (Figs 23 A, K, 24 A, H, 27 E). HEAD. The cephalion (U 1) is clearly demarcated in the body outline, surrounds the mouth ventrally like a bib, and is distinctly flattened and lenticular in the dorsal view (Figs 23 A, K, 24 B, 25 A ‒ C, 26 A, C). Two pairs of cephalic ciliary tufts emerge at U 3 and U 7. In addition, inverted V-shaped streaks of basal bodies extend from the level of the mouth to the posterior level of the hypostomium (Figs 24 A, 26 C). The mouth ring is oval, approximately 5.5 µm in the largest diameter, and located subapically at U 2 – U 5. There are strong but short, rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring (Fig. 26 C). Three inner cuticular teeth are clearly visible, two are located laterally and one apically (Fig. 25 A). The hypostomium (ca U 5 – U 9) is rich in structures, i. e., it is composed of a pentagonal cuticular plate bearing two protuberances (Figs 24 B, 26 C). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 29, is almost 35 µm long and 7.4 - 9.1 µm wide, sinuous, and without dilatations (Figs 25 A, 26 A). The intestine runs from U 29 to U 85 and has a separate, well-differentiated anterior section (U 29 – U 33). Transversal bands connected to the base of dorsal scales are well recognizable. The adhesive gland is placed right behind the terminal part of the intestine (ca U 85 – U 87), forming a short dichotomy at the subtle furca base (Figs 23 K – L, 25 C). SCALES. Almost the entire body is covered by slightly overlapping, mostly three-lobed scales that adhere to the basal cuticle layer along either all or most of their perimeter. Scales are distributed in 14 longitudinal rows, with 30 – 32 scales in the central row. Their size increases slightly in a posterior direction. Central dorsal and dorsolateral longitudinal rows of scales begin at the level of the anterior edge of the cephalion (ca U 1), while lateral rows start at ca U 14 at the posterior edge of the hypopleurae. They run almost along the whole body length (till U 92) (Figs 23 A, 27 B). Ventrolateral rows commence at U 13 due to the highly developed hypopleurae and terminate in the furcal region at ca U 85. Ventral rows commence rather far away from the anterior body end at U 29, because of the strongly developed and apically completely fused bands of locomotory cilia (Figs 24 A, 25 C). Seven main types of dorsal scales were recognized. (i) Head scales (U 2 – U 17) are small (3.1 – 4.1 × 1.6 – 3.0 µm) and have a subtle, well-delimited anterior lobe, comparatively long and diverging posterior lobes, α = 156 – 173 °, β = 55 – 87 ° (Figs 23 B – C, 27 A). (ii) Dorsal neck scales (U 17 – U 27) are boomerang-like with a broadly rounded anterior lobe, elongated posterior lobes, and an indistinct and continuous transition between the anterior and posterior lobes, α = 166 – 173 °, β = 55 – 87 ° (Fig. 23 F). (iii) Dorsolateral neck scales possess a well-delimited, broadly rounded anterior lobe, i. e., the transition between anterior and posterior lobes is distinct, α = ~ 171 °, β = ~ 70 ° (Fig. 23 D). (iv) The main trunk region bears distinctly bigger scales (5.3 – 9.3 × 3.1 – 6.1 µm) whose anterior end is rounded, posterior lobes are comparatively long, narrowly rounded, and diverging, the transition between anterior and posterior lobes is well marked, α = 146 – 176 °, β = 86 – 102 ° (Fig. 23 G). (v) Posterior trunk scales are 8.1 – 8.9 × 4.1 – 4.8 µm in size, their anterior lobe is conspicuously prolonged becoming tongue-shaped, while their posterior lobes are relatively short and taper towards the distal end, the transition between anterior and posterior lobes is slightly marked, α = 140 – 170 °, β = 53 – 68 ° (Figs 23 H, 27 C). (vi) Furca base scales are 4.5 – 8.4 × 2.8 – 3.6 µm in size, their anterior lobe is slightly narrower and more elongated, posterior lobes are short and very narrowly rounded or almost acute distally, the lobe transition is less distinct than in the previous type, α = 149 – 163 °, β = 69 – 78 ° (Fig. 23 J). (vii) Furca branches carry elongated oval, keeled scales measuring 5.7 – 6.0 × 1.7 – 1.8 µm (Fig. 23 I). These scales reach up to the apical margin of the adhesive tubes. SPINES. Dorsal, dorsolateral, lateral, and ventrolateral scales bear simple, slightly curved spines that gradually narrow towards the distal end (Figs 23 A, E, K – L, 25 A – B). The spine emerges rather close to the anterior margin of scales. Spines do not differentiate into various types, only their length slightly increases from 3.5 µm to 10.9 µm in a posterior direction (Supp. file 1: Table S 4). A lateral denticle is not developed. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Ventral ciliary bands commence almost right behind the hypostomium. Their anterior region is conspicuously broad, causing both bands to be completely fused from U 9 to U 27 (Figs 24 A, 26 B – C). However, the middle distal part of the merged ciliary bands more or less follows the course of the posterior margin of the hypostomium, i. e., it is concave from ca U 10 to U 13. Basal bodies are densely packed and do not form regular rows in the anterior fused region of the ciliary bands. The anterior field of basal bodies splits into two distinct ventral bands about at U 27. Locomotory cilia then become regularly arranged in more or less equidistantly spaced horizontal rows. Each row typically consists of seven narrowly spaced basal bodies from ca U 28 to U 83. Rows of basal bodies are lined up with horizontal rows of ventral scales. This regular pattern changes about at U 84 where distances between horizontal ciliary rows gradually decrease. Also, the number of basal bodies per row gradually decreases and ciliary bands terminate at U 88 (Figs 24 A, 25 C). The ciliary bands are accompanied by two ventrolateral rows of three-lobed scales, with an indistinct and continuous transition between the anterior and posterior lobes (Fig. 24 A). The inner row starts at U 22 and consists of smaller scales (2.4 – 4.3 × 1.2 – 2.8 µm) (Fig. 24 E), while the outer row begins at ca U 40 and is built up from bigger scales (4.8 – 5.3 × 2.2 – 3.6 µm) (Fig. 24 D). The ventral interciliary field bears four types of horizontally distributed scales: (i) minute (1.5 – 1.8 × 1.3 – 1.8 µm), tongue-like, double-edged scales with a minute keel (U 28 – U 32); (ii) small (1.9 – 2.3 × 1.6 – 2.1 µm), roughly rectangular, double-edged scales with a keel (U 33 – U 83) (Figs 24 C, 27 D); (iii) slightly bigger (3.9 – 4.4 × 1.0 – 1.5 µm), oblong, doubleedged scales with a short spine (U 83 – U 87); and (iv) a pair of big (6.1 – 7.8 × 2.0 – 3.2 µm), elongated oval scales with a keel (Figs 24 H, 27 E). All ventral interciliary field scales are anteriorly merged into the cuticle. The furca branches carry two types of scales (U 88 – U 95): (i) two pairs of three-lobed, spined scales (3.2 – 5.0 × 1.1 – 2.0 µm), with an elongated, tongue-shaped anterior lobe and comparatively short, narrowly rounded to acute posterior lobes (Fig. 24 F) and (ii) smaller (0.7 – 3.2 × 0.4 – 1.8 µm), cordiform, short-spined scales (Figs 24 G – H, 27 E).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF9EFF8A50AEDFFD2C0EF830.taxon	description	urn: lsid: zoobank. org: act: DD 747096 - A 6 E 0 - 43 F 7 - B 462 - 349692 AAFB 65 Figs 28 ‒ 30; Supp. file 1: Table S 6	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF9EFF8A50AEDFFD2C0EF830.taxon	diagnosis	Morphological diagnosis Body stocky and around 87 – 112 µm long. Head wider than neck, separated from trunk by a more or less distinct neck constriction. Cephalion, epipleurae, and hypopleurae clearly demarcated. Trunk widest at ca U 55, gradually tapers towards furca base (U 83). Mouth ventral, no cuticular teeth. Pharynx without dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, not overlapping, distributed in a minimum of 10 columns, 15 scales per column. Spines with a very short lateral denticle. Scales and spines increase gradually in size in a posterior direction. Dorsal surface covered with: (i) head and upper-neck scales with a small, narrowly rounded anterior lobe and elongated posterior lobes; (ii) lower-neck and anterior trunk scales with a slightly larger anterior lobe and elongated posterior lobes; (iii) posterior trunk scales with an elongated anterior lobe and posterior lobes about as long as anterior lobe; and (iv) posteriormost trunk scales with a tongue-shaped anterior lobe and short posterior lobes. Furca branches shorter than adhesive tubes, lateral margins more or less straight, furcal indentation U-shaped, adhesive tubes long and diverging posteriorly. Dorsal and lateral sides of furca branches covered with narrowly trapezoid, keeled scales with rounded edges and ventral side of furca base and branches covered with (i) a pair of oblong, keeled scales and (ii) three-lobed, spined scales, with an elongated anterior lobe and comparatively short, narrowly rounded posterior lobes, transition between anterior and posterior lobes continuous and indistinct. Molecular diagnosis ITS 2: 36 T, 61 C, 71 T, 72 G, 126 T, 135 A, 164 C, 171 C, 175 A, 176 A, 177 A. Cytochrome c oxidase subunit I: 69 (205 ‒ 207) CTG, 92 (274 ‒ 276) TTG, 109 (325 ‒ 327) GCG, 156 (466 ‒ 468) GCT, 168 (502 ‒ 504) CTA, 174 (520 ‒ 522) GCC, 176 (526 ‒ 528) TTA. Reference molecules are shown inSupp. file 1: Figs S 4, S 10, S 16. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.00 ‒ 4.33 % in 18 S, 10.16 ‒ 34.22 % in ITS 2, 0.26 ‒ 9.61 % in 28 S, and 5.63 ‒ 12.70 % in COI. There are 1 ‒ 16 CBCs (except for Ch. (H). slavicus sp. nov., Ch. (H). iratus sp. nov., and Ch. (H). arcanus sp. nov. where there are no CBCs) in the 18 S rRNA molecule, 1 ‒ 4 CBCs (except for Ch. (H). slavicus sp. nov., Ch. (H). gulosus sp. nov., and Ch. (H). arcanus sp. nov. where there are no CBCs) in the ITS 2 molecule, and 2 ‒ 18 CBCs in the first two domains of the 28 S rRNA gene (except for Ch. (H). slavicus sp. nov., Ch. (H). iratus sp. nov., and Ch. (H). arcanus sp. nov. where there are no CBCs).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF9EFF8A50AEDFFD2C0EF830.taxon	etymology	Etymology The Latin noun ‘ luxus ’ [m] (‘ extravagance, luxury’) refers to the ‘ extravagant’ appearance of the new species. The species group name is treated as a noun in the nominative singular standing in apposition to the generic name (Article 11.9.1.2 of the ICZN 1999).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF9EFF8A50AEDFFD2C0EF830.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (the specimen was destroyed during DNA extraction); Zlaté Piesky lake, municipal recreation area, Ružinov, Bratislava, Podunajská rovina plain; 48 ° 11 ′ 17.1 ″ N, 17 ° 11 ′ 24.3 ″ E. Paratypes SLOVAKIA • 2 adults (photomicrographs); same collection data as for the holotype; CU-FNS- 17 - 02 - 20 / PA- 1, CU-FNS- 18 - 02 - 20 / PA- 2. Photomicrographs of paratype specimens are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. Paratypes are shown in Fig. 30. Type material A DNA sample of the holotype specimen ZPvs 20 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427593). Type locality Zlaté Piesky lake, municipal recreation area, Ružinov, Bratislava, Podunajská rovina plain, 48 ° 11 ′ 17.1 ″ N, 17 ° 11 ′ 24.3 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen ZPvs 20 have been deposited in GenBank under the following accession numbers: OM 421714, OM 421690, and OM 424069, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF9EFF8A50AEDFFD2C0EF830.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) luxus sp. nov. is about 87 – 112 µm long and has a stocky body that is more or less tenpin-shaped, with a clearly defined head region, a narrowing neck, and a rather bulbous trunk (Figs 28 A, 29 A). Body height in lateral view is 13.5 – 14.0 µm at U 10, 16.5 – 16.8 µm at U 50, and 18.0 – 18.2 µm at U 60. The head is relatively wide, with a plate-like cephalion. The neck (ca U 15 – U 28) smoothly continues to the trunk, which is significantly wider than the head, gradually dilates from about U 37 to U 60 where it reaches the maximum width. Then it gradually tapers towards U 81, where curved margins of the furca branches begin to emerge. Dorsal sensory bristles were not observed. The furcal indentation is deeply U-shaped. The furca branches are set apart. Well-developed adhesive tubes are approximately 11 – 13 µm long, slightly curved in lateral view, and run almost in parallel (Figs 28 A, H, 29 A, D – E, 30 A). HEAD. The head is five-lobed. The cephalion (U 1 – U 2) is rounded, clearly demarcated in the body outline, and has a free posterior (dorsal) edge. The epipleurae are formed approximately at U 3 – U 5 while the hypopleurae at U 6 – U 13. The latter structures are clearly demarcated in the head outline (Fig. 28 A, H). Two pairs of cephalic ciliary tufts emerge laterally between the cephalion and the epipleurae edge (ca U 3) as well as between the epi- and the hypopleurae edge (U 6). The hypostomium (ca U 4 – U 6) is free of structures. The mouth ring is oval, 3.2 – 6.0 µm in the largest diameter, located subterminally at U 2 – U 6. There are strong but short rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring (Figs 29 A, 30 A – B). Inner cuticular teeth are not present. INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 34, is 28 – 32 µm long and 5.9 – 8.3 µm wide, sinuous, and has no dilatations (Figs 29 D, 30 A – B). The intestine runs from U 35 to U 82 and has a separate, well-differentiated anterior section (U 35 – U 38). A pair of protonephridia runs from ca U 45 to U 60. Transversal bands connected to the base of dorsal scales are well recognizable (Figs 29 D, 30 A). The adhesive gland (ca U 80 – U 91) is placed right behind the terminal part of the intestine, forming a short dichotomy at the subtle furca base. SCALES. Almost the entire body is covered by not overlapping three-lobed scales that adhere to the basal cuticle layer along their whole perimeter. Scales are distributed in a minimum of 10 longitudinal rows, with 15 scales in the central row. Their size increases gradually in a posterior direction. Central dorsal and dorsolateral longitudinal rows of scales begin at the level of the anterior edge of the epipleurae (ca U 5), while lateral rows start at the posterior end of the hypopleurae (ca U 13). Ventral rows are hardly visible due to the thick, elongated dorsal spines (for further explanation, see below) and long locomotory cilia. Five main types of scales could be recognized with respect to the shape of the anterior lobe. (i) The head and upper-neck scales (U 5 – U 25) are 3.2 – 5.4 × 2.1 – 5.2 µm in size and have a small, narrowly rounded anterior lobe and elongated posterior lobes, α = 153 – 162 °, and β = 75 – 89 ° (Figs 28 B, 30 C). (ii) The lower-neck and anterior trunk scales (U 29 – 42) are 2.6 – 3.5 × 3.7 – 5.8 µm in size and exhibit a slightly larger anterior lobe and elongated posterior lobes, α = 167 – 179 °, and β = 72 – 83 ° (Fig. 28 C). Both types share an indistinct and continuous transition between anterior and posterior lobes. (iii) Posterior trunk scales (U 45 – 80) are 3.8 – 7.4 × 2.4 – 4.2 µm in size and display an elongated anterior lobe, posterior lobes about as long as the anterior lobe and distinctly set off from it, α = 153 – 170 °, β = 75 – 96 ° (Figs 28 D, 30 D). (iv) Posteriormost trunk scales are 4.3 – 5.8 × 2.4 – 3.0 µm in size and have a tongue-shaped anterior lobe and short dilating posterior lobes, α = 144 – 164 °, β = 83 – 85 °. The transition between anterior and posterior lobes is marked (Fig. 28 F). (v) The dorsal and lateral sides of the furca branches bear three pairs of narrowly trapezoid scales with rounded edges. These scales are keeled and have a size of 4.5 – 5.6 × 1.9 – 2.7 µm (Figs 28 G – H, 30 G). SPINES. Spines do not differentiate into various types, only their length increases from 3.4 µm to 13.5 µm in a posterior direction (Supp. file 1: Table S 6). However, the width of individual spines decreases from 0.7 µm at the base to 0.2 µm at the tip and, hence, spines do not become hair-like terminally. The spine base is situated near the anterior margin of scales. All spines are distinctly curved and bear an inconspicuous lateral denticle (Figs 28 A, E, H, 29 A, D, 30 D – E). The lateral denticle emerges comparatively near the spine apex, i. e., the d - value ranges only from 0.9 ‒ 1.5 μm, which corresponds to a d ratio of 5.8 ‒ 7.4 %. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Unfortunately, the ventral side could not be observed in detail due to the thickness and stiffness of dorsal spines, which precluded turning over and squeezing the worms. Moreover, the ventral locomotory cilia also hampered detailed observations of the ventral side. Despite these difficulties, the following observations were conducted. The longitudinal ciliary bands begin at ca U 10 and run backward to ca U 84. The ciliary bands are accompanied from U 13 to U 75 by two ventrolateral rows of small (1.4 – 4.4 × 1.4 – 2.8 µm in size), three-lobed scales (α = 160 – 167 °, β = 79 – 85 °) equipped with relatively long spines (6.6 – 9.6 µm) (Fig. 29 A – B). The furcal region (U 81 – U 91) carries two types of scales (Figs 29 A, C, E, 30 F): (i) a pair of oblong, keeled scales being 6.8 – 7.0 × 2.8 – 3.0 µm in size and (ii) three-lobed, spined scales (1.9 – 3.8 × 1.5 – 2.3 µm), with an elongated anterior lobe and comparatively short, narrowly rounded posterior lobes, the transition between the anterior and posterior lobes is continuous and indistinct, α = 158 – 172 °, and β = 73 – 84 °.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF98FF8550A8DC362C0EFDC8.taxon	description	urn: lsid: zoobank. org: act: 1 A 749 F 30 - 3 FDF- 4 A 02 - 8923 - 1 DAE 313 BAB 8 E Figs 31 ‒ 32; Supp. file 1: Table S 7	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF98FF8550A8DC362C0EFDC8.taxon	diagnosis	Morphological diagnosis Body elongated and about 124 µm long. Head slightly wider than neck, separated from trunk by an inconspicuous neck constriction. Cephalion, epipleurae, and hypopleurae clearly demarcated. Trunk widest at ca U 61, gradually tapers towards furca base (U 82). Mouth ventral, one central cuticular tooth. Hypostomium bears two parallel, horizontally arranged lamellae accompanied by tear-shaped protuberances. Pharynx without dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, slightly overlapping, distributed in about 12 columns, 22 scales per column. Scales and spines increase gradually in size in a posterior direction. Dorsal surface covered by scales from posterior end of cephalion (ca U 4) to furca branches (ca U 83). Furca branches slightly shorter than adhesive tubes, lateral margins more or less straight, furcal indentation V-shaped, adhesive tubes comparatively short. Molecular diagnosis 18 S rRNA gene: 1716 C. ITS 2: 38 C, 61 T, 67 C, 68 A, 85 T, 86 G, 91 C, 103 C, 113 T, 114 A, 124 A, 129 G, 155 C. 28 S rRNA gene: 465 C, 656 T, 674 G. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 123 (367 ‒ 369) GTG, 159 (475 ‒ 477) CGG, 186 (556 ‒ 558) CTA, 216 (646 ‒ 648) ATC. Reference molecules are shown in Supp. file 1: Figs S 5, S 11 A, S 17. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.05 ‒ 4.33 % in 18 S, 14.44 ‒ 37.76 % in ITS 2, 0.25 ‒ 9.79 % in 28 S, and 5.62 ‒ 12.74 % in COI. There are 1 ‒ 16 CBCs (except for Ch. (H). arcanus sp. nov., Ch. (H). luxus sp. nov., and Ch. (H). slavicus sp. nov., where there are no CBCs) in the 18 S rRNA molecule, 1 ‒ 3 CBCs in the ITS 2 molecule, and 1 ‒ 18 CBCs in the first two domains of the 28 S rRNA molecule (except for Ch. (H). luxus sp. nov. and Ch. (H). slavicus sp. nov., where there are no CBCs).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF98FF8550A8DC362C0EFDC8.taxon	etymology	Etymology The Latin adjective ‘ iratu · us, - a, - um ’ [m, f, n] (‘ angry, irate’) refers to the spiny appearance of the new species.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF98FF8550A8DC362C0EFDC8.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (photomicrographs, hologenophore); Shallow section of the River Váh, Stankovany, Veľká Fatra Mts; 49 ° 08 ′ 26.3 ″ N, 19 ° 10 ′ 14.6 ″ E; CU-FNS- 21 - 09 - 20 / HO. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The holotype is shown in Fig. 32. Type material A DNA sample of the holotype specimen STV 65 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427609). Type locality Shallow section of the River Váh near the village of Stankovany, Veľká Fatra Mts, Slovakia, 49 ° 08 ′ 26.3 ″ N, 19 ° 10 ′ 14.6 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen STV 65 have been deposited in GenBank under the following accession numbers: OM 421720, OM 421696, and OM 424075, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF98FF8550A8DC362C0EFDC8.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) iratus sp. nov. is about 124 µm long and has a slender elongated body, with a head region slightly broader than the neck and trunk (Figs 31 A, J, 32 A). Body width is about 21.5 µm at U 10, 20.0 µm at U 50, and 22.5 µm at U 60. The head is relatively wide (20.2 µm at U 6), with a plate-like cephalion. Epi- and hypopleurae are clearly demarcated in the head outline (Figs 31 A, J, 32 A). The neck (ca U 13 – U 34) is only inconspicuously marked and smoothly continues to the trunk. In comparison with the head, the trunk is comparatively slender, gradually dilatating from about U 35 to U 61, where it reaches the maximum width. Then, the trunk gradually narrows towards U 82, where more or less straight margins of the furca branches start to form. Dorsal sensory bristles were not observed. The furcal indentation is deeply V-shaped and approximately 19.4 µm long. Welldeveloped adhesive tubes are straight and approximately 10.7 µm long (Fig. 31 A, J). HEAD. The cephalion (U 1) is clearly demarcated in the body outline, distinctly flattened, and surrounds the mouth ventrally like a bib. The epipleurae are formed approximately at U 3 – U 7 while the hypopleurae at U 8 – U 14. The latter structures are well recognizable in the head outline (Figs 31 A, J, 32 A). Two pairs of cephalic ciliary tufts (6.9 – 18.8 µm) emerge laterally between the cephalion and the epipleurae edge (ca U 3) as well as between the epi- and the hypopleurae edge (U 7). The mouth ring is oval, approximately 6.9 µm in the largest diameter, and located subapically at U 2 – U 5. There are strong but short, rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring (Figs 31 I – J, 32 C, F). One cuticular tooth is clearly visible in the center of the mouth ring (Figs 31 I, 32 F). The hypostomium (ca U 5 – U 9) is composed of two more or less parallel, horizontally arranged lamellae whose lateral sides are accompanied by tear-shaped protuberances. Moreover, the lateral sides of the hypostomium are lined from U 3 to U 8 by relatively wide patches of irregularly arranged basal bodies (Figs 31 I, 32 F). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 31, is 28 µm long and 6.2 – 8.8 µm wide, sinuous, and without dilatations (Figs 31 J, 32 A – B). The intestine runs from U 22 to U 87 and has a separate, well-differentiated anterior section (U 32 – U 35). Transversal bands connected to the base of dorsal scales are well recognizable. The adhesive gland is placed right behind the terminal part of the intestine (ca U 85 – U 87), forming a short dichotomy at the subtle furca base. SCALES AND SPINES. Almost the entire body is covered by slightly overlapping, mostly three-lobed scales that adhere to the basal cuticle layer along either all or most of their perimeter. Scales are very densely packed, forming a minimum of 12 longitudinal rows on the dorsal side, with 22 scales in the central row. They have a rounded anterior lobe and elongated posterior lobes narrowly rounded distally. The transition between the anterior and posterior lobes is marked except for the ventro- and dorsolateral scales in which the transition is indistinct (Fig. 31 D ‒ G). The size of scales increases from 2.3 × 2.1 µm to 7.4 × 3.1 µm in a posterior direction. Dorsal furca branches scales are 4.3 × 3.4 µm in size, threelobed and spined but their anterior lobe is more elongated, their posterior lobes are slightly shorter and narrower, the transition between the anterior and posterior lobes is continuous and indistinct (Fig. 31 H). Spines do not differentiate into various types, only their length slightly increases from 2.3 µm to 6.5 µm in a posterior direction (Figs 31 A ‒ H, J, 32 A, D, Supp. file 1: Table S 7). Spines are slightly narrower posteriorly but do not become hair-like terminally. A lateral denticle is not developed (Figs 31 B – C, 32 A, D). VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Ventral ciliary bands commence almost right behind the hypostomium (U 10) and terminate at ca U 87. Their anterior region is broadened as typical of most species described herein. The ciliary bands are accompanied by two ventrolateral rows of threelobed scales that start at U 13. They are 3.6 – 5.3 × 2.5 – 3.1 µm in size and have a similar morphology as the dorsal and dorsolateral scales but the transition between the anterior and posterior lobes is continuous and hence indistinct (Fig. 31 G). Unfortunately, no further features of the ventral side were observed.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF94FFFF50A3DF9B2DA4F9C7.taxon	description	urn: lsid: zoobank. org: act: 5 B 6 AE 48 A- 9 F 1 F- 4 F 7 A- 8054 - A 01 F 7 AB 19 E 9 B Figs 33 ‒ 36; Supp. file 1: Table S 8	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF94FFFF50A3DF9B2DA4F9C7.taxon	diagnosis	Morphological diagnosis Body stocky and around 107 µm long. Head wider than neck, separated from trunk by a distinct neck constriction. Cephalion and epipleurae clearly demarcated, hypopleurae only inconspicuously marked. Trunk widest at ca U 50, gradually tapers towards furca base (U 80). Mouth ventral, no cuticular teeth. Hypostomium bears two parallel cuticular lamellae. Pharynx without dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, not overlapping, distributed in 14 columns, 12 scales per column. Scales and spines increase gradually in size in a posterior direction. Dorsal surface covered with: (i) small head and anterior neck scales with a small, broadly rounded anterior lobe, equally long posterior lobes, and marked transition between anterior and posterior lobes; (ii) small posterior neck scales with a slightly elongated anterior lobe and an indistinct transition between anterior and posterior lobes; and (iii) comparatively big and triangular trunk scales. Interciliary field covered by (i) small, oval to oblong scales without keels; (ii) a pair of small, oval scales with a keel; (iii) a single distinctly bigger, oblong, and keeled scale; and (iv) a pair of big, very narrowly ovate, and spined scales. Furca branches about as long as adhesive tubes, with lateral margins more or less straight, furcal indentation shallowly U-shaped, adhesive tubes well-developed. Ventral side of furca branches covered with minute, oval to oblong, and keeled scales. Molecular diagnosis 18 S rRNA gene: 1378 A. ITS 2: 78 T, 128 T, 155 ‒, 172 A, 174 C, 186 ‒. 28 S rRNA gene: 503 C. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 20 (58 ‒ 60) TTA, 45 (133 ‒ 135) GTG, 71 (211 ‒ 213) CCG, 74 (220 ‒ 222) ATC, 94 (280 ‒ 282) CCA, 143 (427 ‒ 429) TCA, 151 (451 ‒ 453) TTC, 157 (469 ‒ 471) AAT, 168 (502 ‒ 504) CTC, 178 (532 ‒ 534) ACT, 180 (538 ‒ 540) GTT, 204 (610 ‒ 612) ACA, 209 (625 ‒ 627) CCA, 214 (640 ‒ 642) GAT. Reference molecules are shown in Supp. file 1: Figs S 6, S 11 B, S 18. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.33 ‒ 4.22 % in 18 S, 6.95 ‒ 29.95 % in ITS 2, 1.46 ‒ 8.84 % in 28 S, and 8.57 ‒ 13.14 % in COI. There are 1 ‒ 15 CBCs in the 18 S rRNA molecule, 1 ‒ 4 CBCs in the ITS 2 molecule (except for Ch. (H.) arcanus sp. nov., Ch. (H.) luxus sp. nov., and Ch. (H.) slavicus sp. nov., where there are no CBCs), and 2 ‒ 17 CBCs in the first two domains of the 28 S rRNA molecule.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF94FFFF50A3DF9B2DA4F9C7.taxon	etymology	Etymology The Latin adjective ‘ gulos · us, - a, - um ’ [m, f, n] (‘ gluttonous’) refers to the stocky appearance of the new species.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF94FFFF50A3DF9B2DA4F9C7.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (the specimen was destroyed during DNA extraction); Vajspeterský potok creek, Rača, Bratislava, Podunajská rovina plain; 48 ° 12 ′ 12.8 ″ N, 17 ° 07 ′ 46.9 ″ E. Paratype SLOVAKIA • adult (photomicrographs); same collection data as for holotype; CU-FNS- 28 - 10 - 19 / PA. Photomicrographs of the paratype specimen are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The paratype is shown in Figs 35 – 36. Type material A DNA sample of the holotype specimen VP 18 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427574). Type locality Vajspeterský potok creek, Rača, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 12 ′ 12.8 ″ N, 17 ° 07 ′ 46.9 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen VP 18 have been deposited in GenBank under the following accession numbers: OM 421721, OM 421697, and OM 424076, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFF94FFFF50A3DF9B2DA4F9C7.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) gulosus sp. nov. is about 107 µm long and has a stocky body that is tenpin-shaped, with a clearly defined head region, a narrowing neck, and a rather bulbous trunk (Fig. 33 A – B). Body width is ca 18 µm at U 10, ca 26 µm at U 50, and ca 29 µm at U 60. The head is relatively wide, with a plate-like, slightly narrower cephalion. The neck (ca U 13 – U 27) smoothly continues to the trunk, which is distinctly wider than the head, gradually dilates from about U 37 to U 50 where it reaches the maximum width. Then it gradually tapers towards U 80 where the curved margins of the furca branches begin to emerge. Dorsal sensory bristles arise from the cuticle in two pairs at U 23 and U 60 (Fig. 33 A). The furcal indentation is deeply U-shaped. The furca branches are set apart and diverge posteriorly. Well-developed adhesive tubes are approximately 9 µm long and more or less straight (Figs 33 A – B, 35 C, 36 C). HEAD. The head is roughly five-lobed. The cephalion (U 1 – U 2) is rounded, clearly demarcated in the body outline (Figs 33 A – B, 34 A). The epipleurae are formed approximately at U 3 – U 6, the hypopleurae are only inconspicuously marked. Two pairs of cephalic ciliary tufts emerge laterally between the cephalion and the anterior edge of the epipleurae (ca U 3) as well as close to the posterior edge of the epipleurae (U 6). The mouth ring is oval, ca 4.6 µm in the largest diameter, located subterminally at U 2 – U 4. There are strong, rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring (Figs 33 B, 35 B). Inner cuticular teeth are not present. The hypostomium (ca U 6 – U 9) is in a form of two parallel horizontal cuticular lamellae laterally lined with a few ciliary patches (Fig. 33 B). Each field is composed of several irregular groups of basal bodies (Figs 33 B, 35 B). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 27, is about 28 µm long and 6.5 – 8.9 µm wide, sinuous, and has no dilatations. The cerebral ganglion appears as a mass surrounding the pharynx along its whole length. The intestine runs from U 27 to U 81 and has a separate, well-differentiated anterior section (U 28 – U 31). A pair of protonephridia runs from ca U 32 to U 40 (Fig. 35 C). Transversal bands connected to the base of dorsal scales are well recognizable. The adhesive gland (ca U 85 – U 91) is placed right behind the terminal part of the intestine, forming a short dichotomy at the subtle furca base (Fig. 35 C). SCALES. Almost the entire body is covered by not overlapping three-lobed scales that adhere to the basal cuticle layer along their whole perimeter. Scales are distributed in 14 longitudinal rows, with 13 scales in the central dorsal row. Their size increases in a posterior direction. Central dorsal and dorsolateral longitudinal rows of scales begin at ca U 5 (behind the posterior edge of the cephalion), while lateral rows start at the posterior end of the epipleurae (ca U 13). Ventral rows start at U 10 and exhibit a horizontal zonation pattern. Four main types of scales could be recognized with respect to the shape of the anterior lobe. (i) The head and anterior neck scales (U 5 – U 28) are 3.1 – 3.5 × 2.0 – 2.3 µm in size, have a small, broadly rounded anterior lobe and equally long posterior lobes, the transition between the anterior and posterior lobes is marked, α = ~ 156 °, and β = ~ 123 ° (Fig. 34 A). (ii) The posterior neck scales (U 29 – 42) are 2.7 – 4.3 × 2.4 – 3.1 µm in size, exhibit a slightly elongated anterior lobe and an indistinct and continuous transition between the anterior and posterior lobes, α = ~ 167 °, and β = ~ 98 ° (Fig. 34 B). (iii) The trunk scales (U 37 – 80) are comparatively big (6.2 – 7.1 × 4.5 – 5.4 µm), triangular, and display a continuous and indistinct transition between the anterior and posterior lobes, α = 168 – 172 °, and β = 96 – 102 ° (Figs 34 C, 35 D, 36 B). Dorsolateral trunk scales are 7.4 – 8.4 × 4.0 – 4.4 µm in size and resemble anterior trunk scales (Fig. 34 D). (iv) The trunk lateral scales are 5.5 – 5.9 × 3.7 – 3.8 µm in size, distinctly three-lobed, all lobes are narrowly rounded to more or less tapered, and the transition between the anterior and posterior lobes is marked (Fig. 34 E). SPINES. All spines bear a distinct lateral denticle and gradually narrow towards their distal end (Figs 33 A – B, 34 A ‒ F). Keels start close to the anterior margin of scales. Spines are not straight but distinctly curved (Fig. 35 C – D). They do not differentiate into various types, only their length increases from 3.1 μm to 14.0 μm in a posterior direction (Supp. file 1: Table S 8). The lateral denticle is comparatively distant from the spine apex, i. e., the d - value ranges from 1.0 ‒ 3.1 μm, which corresponds to a d ratio of 7.5 ‒ 25 %. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Ciliary bands start at U 10 where they are conspicuously broad. However, they begin to narrow from U 25 and terminate at U 80. The ciliary bands are accompanied by two ventrolateral rows of three-lobed scales that extend from U 12 to U 80 (Fig. 33 B). They are 1.5 – 4.3 × 1.1 – 3.2 µm in size and have a marked transition between the anterior and posterior lobes, α = 149 – 160 °, and β = 62 – 100 ° (Fig. 34 F). The ventral interciliary field bears four types of horizontally distributed scales: (i) small (2.7 – 4.3 × 3.1 – 3.4 µm), oval to oblong, double-edged scales without keels (U 10 – U 73) (Figs 33 B, 34 H, 36 A); (ii) a pair of relatively small (4.4 – 5.1 × 2.6 – 2.7 µm), oval, double-edged, and keeled scales (U 74); (iii) a single oblong (1.3 – 2.0 × 1.0 – 1.5 µm), centrally positioned, double-edged, and keeled scale (U 71); and (iv) a pair of big (11.8 – 12.3 × 3.2 – 3.4 µm), very narrowly ovate, double-edged, and spined scales (U 76) (Figs 34 G, 36 D). The furca branches (U 81 – U 90) carry minute (1.1 – 3.2 × 0.5 – 1.4 µm), oval to oblong, and keeled scales (Figs 34 I, 36 C).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEEFFFB509DDBA6287DF836.taxon	description	urn: lsid: zoobank. org: act: ACDC 5 C 8 E-E 066 - 4 BA 7 - B 360 - E 4 EC 7549790 B Figs 37 ‒ 38; Supp. file 1: Table S 9	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEEFFFB509DDBA6287DF836.taxon	diagnosis	Morphological diagnosis Body stocky and around 100 µm long. Head wider than neck, separated from trunk by a distinct neck constriction. Clearly demarcated cephalion, epipleurae and hypopleurae inconspicuously marked. Trunk widest at ca U 37, gradually tapers towards furca base (U 82). Mouth almost apical, no cuticular teeth. Hypostomium bears a single small boomerang-like cuticular structure. Pharynx with delicate dilatations. Intestine straight, with a marked anterior section. Scales spined, three-lobed, not overlapping, distributed in about 12 columns, 14 scales per column. Spines with a short lateral denticle. Scales and spines increase gradually in size in a posterior direction. Dorsal surface covered by scales from posterior end of cephalion (ca U 3) to furca branches (ca U 73). Furca branches slightly longer than adhesive tubes, lateral margins more or less straight, furcal indentation deeply U-shaped, adhesive tubes well-developed. Molecular diagnosis ITS 2: 163 G, 172 T. 28 S rRNA gene: 562 A, 693 C. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 58 (172 ‒ 174) ATA, 97 (289 ‒ 291) ACG, 122 (364 ‒ 366) GTA, 167 (499 ‒ 501) CGG, 174 (520 ‒ 522) GCG, 181 (541 ‒ 543) CTG, 184 (550 ‒ 552) TTA, 185 (553 ‒ 555) TCA, 193 (577 ‒ 579) ATC. Reference molecules are shown in Supp. file 1: Figs S 7, S 12 A, S 19. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p - distance from species described in the present study is 0.00 ‒ 4.33 % in 18 S, 5.88 ‒ 28.88 % in ITS 2, 0.51 ‒ 7.12 % in 28 S, and 8.44 ‒ 12.59 % in COI. There are 1 ‒ 16 CBCs (except for Ch. (H). iratus sp. nov., Ch. (H). luxus sp. nov., and Ch. (H). slavicus sp. nov., where there are no CBCs) in the 18 S rRNA molecule, 1 ‒ 3 CBCs in the ITS 2 molecule (except for Ch. (H). gulosus sp. nov., Ch. (H). luxus sp. nov., and Ch. (H). slavicus sp. nov., where there are no CBCs), and 1 ‒ 18 CBCs in the first two domains of the 28 S rRNA molecule (except for Ch. (H). luxus sp. nov. and Ch. (H). slavicus sp. nov., where there are no CBCs).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEEFFFB509DDBA6287DF836.taxon	etymology	Etymology The Latin adjective ‘ arcan · us, - a, - um ’ [m, f, n] (‘ hidden’) refers to the morphological similarity of the new species with C. (H.) superbus sp. nov.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEEFFFB509DDBA6287DF836.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (photomicrographs, hologenophore); shallow section of the River Váh, Stankovany, Veľká Fatra Mts; 49 ° 08 ′ 26.3 ″ N, 19 ° 10 ′ 14.6 ″ E; CU-FNS- 29 - 09 - 20 / HO. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. The holotype is shown in Fig. 38. Type material A DNA sample of the holotype specimen STV 67 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427571). Type locality Shallow section of the River Váh near the village of Stankovany, Veľká Fatra Mts, Slovakia 49 ° 08 ′ 26.3 ″ N, 19 ° 10 ′ 14.6 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen STV 67 have been deposited in GenBank under the following accession numbers: OM 421723, OM 421699, and OM 424078, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEEFFFB509DDBA6287DF836.taxon	description	Description HABITUS. Chaetonotus (Hystricochaetonotus) arcanus sp. nov. is about 100 µm long and has a stocky, tenpin-shaped body, with a clearly defined head region, a narrowing neck, and a rather bulbous trunk (Figs 37 A, H, 38 B). Body width is ca 19.8 µm at U 10, ca 15.6 µm at U 50, and ca 17.8 µm at U 60. The head is relatively wide (19.8 µm at U 10), with a plate-like, rounded cephalion. The neck (ca U 17 – U 27) is rather inconspicuously marked and smoothly continues to the trunk. The trunk gradually dilatates from about U 35 to U 61, where it reaches the maximum width that is only slightly narrower than the maximum width of the head. Then, the trunk gradually narrows towards U 82, where curved margins of the furca branches begin to emerge. Dorsal sensory bristles were not observed. The furcal indentation is deeply U-shaped. The furca branches are set apart and diverge posteriorly. Well-developed adhesive tubes are approximately 9.4 µm long and straight (Figs 37 A, H, 38 D). HEAD. The cephalion (U 1) is rounded, clearly demarcated in the body outline (Fig. 37 A). The epipleurae (U 3 ‒ U 6) and hypopleurae (U 6 ‒ U 10) are only inconspicuously marked. Pairs of cephalic ciliary tufts emerge laterally at U 3 and U 5. The mouth ring is oval, ca 5.2 µm in the largest diameter, and located subterminally at U 2 – U 5. There are strong but short, rod-like reinforcements lining the walls of the mouth ring and inner delicate structures directed towards the center of the mouth ring. Inner cuticular teeth are not present. The hypostomium (ca U 5 – U 9) carries a small cuticular boomerang-like structure. The lateral sides of the hypostomium are lined by a relatively wide pair of basal body patches (from U 3 to U 8) (Figs 37 G, 38 E). INTERNAL MORPHOLOGY. The pharynx extends from ca U 5 to U 34, is 28 – 29 µm long and 4.6 – 7.2 µm wide, sinuous, with inconspicuously marked anterior and posterior dilatations (Figs 37 H, 38 B). The cerebral ganglion appears as a mass surrounding the pharynx along its whole length. The intestine runs from U 35 to U 82. The adhesive gland (ca U 82 – U 91) is placed right behind the terminal part of the intestine, forming a short dichotomy at the subtle furca base. SCALES. Almost the entire body is covered by not overlapping three-lobed scales (U 3 – U 73) that adhere to the basal cuticle layer along their whole perimeter. Scales are distributed in about 12 longitudinal rows, with 14 scales in the central row. Their size increases gradually from 3.0 – 4.5 × 1.9 – 2.2 µm to 4.9 – 5.6 × 4.1 – 4.3 µm in a posterior direction (Supp. file 1: Table S 9). Central dorsal and dorsolateral longitudinal rows of scales begin at ca U 3, while lateral rows start at ca U 13. Two main types of scales could be recognized concerning the shape of the anterior lobe. (i) The head, neck, and upper-trunk scales (U 3 – U 37) have a narrowly rounded anterior lobe and elongated posterior lobes, α = 156 – 163 °, and β = 54 – 85 °. The transition between the anterior and posterior lobes is indistinct and continuous, providing the scales with an A-shaped appearance (Figs 37 B, D, 38 C). (ii) The posterior trunk scales (U 50 – 73) exhibit a broadly rounded anterior lobe and elongated posterior lobes, α = 153 – 167 °, and β = 75 – 96 °. The transition between the anterior and posterior lobes is marked unlike in the first scale type (Fig. 37 F). SPINES. All spines bear a distinct lateral denticle and gradually narrow towards their distal end. Keels start comparatively close to the anterior margin of scales. Spines are not straight but slightly curved. They do not differentiate into various types, only their length increases in a posterior direction (Figs 37 A, C, E, H, 38 A – B, Supp. file 1: Table S 9). More specifically, the length increase is rather inconspicuous and gradual from the head (3.1 µm) to the posterior neck region (5.8 µm). The most pronounced length change occurs at the beginning of the trunk (ca U 50), where dorsal spines increase significantly from 5.8 µm to 15.2 µm (Figs 37 A, H, 38 B). The lateral denticle is comparatively distant from the spine apex, i. e., d - value ranges from 1.2 – 3.0 μm, which corresponds to a d ratio of 16.7 ‒ 23.3 %. VENTRAL CILIARY BANDS AND VENTRAL INTERCILIARY FIELD. Unfortunately, the ventral side was not observed in detail.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEBFFF9509DDC362A25FC97.taxon	description	urn: lsid: zoobank. org: act: 9826403 E- 1298 - 4889 - 8 E 0 B- 3 A 19 A 9 EFB 3 AE Fig. 9	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEBFFF9509DDC362A25FC97.taxon	diagnosis	Molecular diagnosis 18 S rRNA gene: 1548 A. ITS 2: 52 G, 107 C, 115 A, 156 C, 171 A. Cytochrome c oxidase subunit I (codon ordinal numbers are followed by the corresponding span of nucleotide positions in parentheses): 9 (25 ‒ 27) TTC, 65 (193 ‒ 195) TTC, 96 (286 ‒ 288) CTG, 100 (298 ‒ 300) CTG, 143 (427 ‒ 429) TCC, 161 (481 ‒ 483) GCC. Reference molecules are shown in Supp. file 1: Figs S 8, S 12 B, S 20. All diagnostic molecular autapomorphies are marked by arrows. Reference alignments with corresponding nucleotide positions are in Supp. file 1: Alignments 1 ‒ 4. The p- distance from species described in the present study is 0.05 ‒ 4.38 % in 18 S, 5.88 ‒ 31.02 % in ITS 2, 0.52 ‒ 9.78 % in 28 S, and 7.85 ‒ 13.59 % in COI. There are 1 ‒ 16 CBCs (except for Ch. (H). arcanus sp. nov., Ch. (H). iratus sp. nov., and Ch. (H). luxus sp. nov., where there are no CBCs) in the 18 S rRNA molecule, 1 ‒ 3 CBCs in the ITS 2 molecule (except for Ch. (H). arcanus sp. nov., Ch. (H). gulosus sp. nov., and Ch. (H). luxus sp. nov., where there are no CBCs), and 2 ‒ 18 CBCs in the first two domains of the 28 S rRNA gene (except for Ch. (H). arcanus sp. nov., Ch. (H). iratus sp. nov., and Ch. (H). luxus sp. nov., where there are no CBCs).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEBFFF9509DDC362A25FC97.taxon	etymology	Etymology The Latin adjective ‘ slavic · us, - a, - um ’ [m, f, n] (‘ Slavic’) refers to the type locality (Devín castle) of the new species, which is an important place in Slovak history.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEBFFF9509DDC362A25FC97.taxon	materials_examined	Material examined Holotype SLOVAKIA • adult (the specimen was destroyed during DNA extraction); temporary pond in the floodplain area of the River Morava, Devín, Bratislava, Podunajská rovina plain; 48 ° 10 ′ 29.4 ″ N, 16 ° 58 ′ 35.8 ″ E. Paratypes SLOVAKIA • 3 adults (the specimens were destroyed during DNA extraction); same collection data as for holotype. Photomicrographs of the holotype are available at the Department of Zoology, Comenius University in Bratislava at https: // fns. uniba. sk / en / gastrotricha /. Type material A DNA sample of the holotype specimen DB 40 has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427570). Type locality Ephemeral pond in the floodplain area of the River Morava near the foothill of the Devín castle, Bratislava, Podunajská rovina plain, Slovakia, 48 ° 10 ′ 29.4 ″ N 16 ° 58 ′ 35.8 ″ E. Gene sequences The nuclear 18 S and ITS 1 - 5.8 S-ITS 2 - 28 S rDNA sequences as well as the mitochondrial COI sequence of the holotype specimen DB 40 have been deposited in GenBank under the following accession numbers: OM 421724, OM 421700, and OM 424079, respectively.	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
03D72F3EFFEBFFF9509DDC362A25FC97.taxon	discussion	Remarks Unfortunately, all our attempts for thorough morphological investigations of this species failed. Without a name, Ch. (H.) slavicus sp. nov. would be nothing but a label and nucleotide sequences in the GenBank database. However, this entity can be clearly separated from other species by the combination of 18 S, ITS region, 28 S, and COI sequences. Moreover, it represents a distinct lineage in multi-gene phylogenies (Fig. 9). As ICZN (1999) allows that any part of an animal is eligible to be a name-bearing type (Article 72.5.1), we interpret the isolated DNA as a part of an animal and use it as type material. This strategy is also used in protists whose names are governed by the Zoological Code (e. g., Lynn et al. 2018; Pecina & Vďačný 2022). It is important to mention that the principle of priority applies even if any part of an animal is named before the whole animal (Article 23.3.2.1).	en	Križanová, Františka Rataj, Vďačný, Peter (2022): A huge undescribed diversity of the subgenus Hystricochaetonotus (Gastrotricha, Chaetonotidae, Chaetonotus) in Central Europe. European Journal of Taxonomy 840: 1-93, DOI: https://doi.org/10.5852/ejt.2022.840.1941, URL: http://dx.doi.org/10.5852/ejt.2022.840.1941
