Characella poecillastroides new species

Figures 6a–d, 7a–e

Material examined. Holotype: RMNH Por. 9247, Caribbean Netherlands, Bonaire, Curoil Dock (Dive 3), 112.137°N 68.286°W, on a coral rock wall at 168 m, coll. L.E. Becking & E. Meesters, field nr. BON3/ BDR031, 31 May 2013.

Description. Thickly massive, folded plate (Figs. 6a–c) of 2–4 cm thick and approximately 20–40 cm in lateral expansion. A fragment of 8 x 2 x 2.5 cm was preserved. Rough/hispid surface due to protruding spicules, which cause strong accumulation of sediment. No oscules visible. Color beige alive underneath greyish sediment layer, white-beige after preservation. Consistency hard, rough, but can be torn rather easily.

Skeleton. Radiate skeleton of long oxeas (Fig. 6d), with a relatively low presence of calthrops-like shortshafted triaenes. Microxeas form a rather dense cover at the surface and are abundantly strewn in the choanosome.

Spicules. Calthrops, oxeas, amphiasters, microxeas.

Calthrops-like short shafted triaenes (Fig. 7a), cladi straight or curved, in a large size range, cladomes 400- 598 - 800 µm, cladi 200– 345 –500 x 20– 27 – 30 µm.

Oxeas (Fig. 7b), smooth, usually somewhat curved, 2600– 3120 –3800 x 35– 46.5 – 62.5 µm.

Amphiasters (Fig. 7c), rugose/spined all over, 10– 17 – 25 µm, with 10–16 rays of 2.5– 6 – 10 µm long.

Microxeas, microspined/rugose, in two size classes, larger ones (1, Fig. 7d, 7d 1), gently curved and with tapering sharp ends, 170– 232 –275 x 4– 7 – 10 µm, and short ones (2, Fig. 7e, 7e 1), abruptly curved and/or centrotylote, 25– 37 –45 x 2–3 µm.

Ecology and distribution. The holotype was collected on a carbonate rock wall just below the mesophotic zone off Bonaire.

Etymology. The name refers to the plate-like shape which is unusual in the genus Characella, but is characteristic for the related genus Poecillastra .

Remarks. The new species is assigned to Characella because of the occurrence of two microxea categories and the predominance of amphiaster microscleres (cf. Cárdenas & Rapp 2012). The habit resembles that of a Poecillastra, but that genus has a single microxea category and diverse streptasters including spirasters. Barbados Poecillastra sollasi sensu Van Soest & Stentoft, 1988: 36 (not sensu Topsent 1890) also has this habit, but differs in having metasters and spirasters, next to amphiasters. This Barbados material was discussed by Cárdenas & Rapp (2012), who pointed out that the species appears intermediate between Poecillastra and Characella in having two sizes of microxeas next to diverse streptasters. Apparently, habit is not a good marker for the two genera, which have been demonstrated to be distinct genetically (Cárdenas et al. 2011). Characella aspera Sollas, 1886 as reported by Van Soest & Stentoft (1988: 38) from Barbados appears close in spiculation to C. poecillastroides n. sp., but is radically different in habit (see Table 2 and Figs 21a 1, 21a 2). Several specimens were collected during the present submarine dives (BDR027 and 036).