Diagnosis
provided by World Register of Marine Species
Hyocrinidae with basals 3 or fused, forming a circlet without distinct sutures. Width of distal radial articular facet 33 to 44 percent of upper width of radial. No lateral spines or flattened projections on proximal brachials and pinnulars. Second and third nonmuscular articulations between brachials 3-4 and 5-6. First pinnule typically on brachial 6, rarely on 5. Successive series of 2-3 brachials united by synostosis in mid-arm, never successive muscular articulations. Expansion of genital pinnules with one row of H-shaped plates, but shape of cover plates very variable and useful at species level only (Roux, 2004, fig. 7). Cover plates consisting of 2-3 pairs corresponding to each pinnular. Tegmen typically low, sometimes inflated. Oral plates typically large, forming high oral cone where tegmen low. Anal cone low. Columnal symplexies with 6-10 crenular units of one crenula each, or more in larger species such as H. biscoitoi (number of crenular units and crenulae unknown in H. giganteus).
