Order Isocrinida Sieverts-Doreck, 1952

Remarks. The classification of Isocrinida retained by Hess (2011) is based on plesiomorphic characters without phylogenetic significance (Roux et al. 2009; Améziane et al. 2021). Pending a new classification based on both morphology and molecular data with a redefinition of the different families of Isocrinida (Améziane et al. in prep.), we group the subfamilies here cited in the single family Isocrinidae . Roux (1977) has shown that the characters of stalk symplexies differentiated the extant genera. Species belonging to the same genus differ in having peculiar characters of infranodal cryptosymplexies (see also Roux 1981; David et al. 2006). Changes during columnal ontogeny such as increase in number of crenulae per petaloid zone, closure of petaloid zones and closure of axial interpetaloid furrow in symplexy should be taken into account.