Holopus d’Orbigny, 1837

Donovan, Stephen K. & Pawson, David L., 2008, A new species of the sessile crinoid Holopus d’Orbigny from the tropical western Atlantic, with comments on holopodid ecology (Echinodermata: Crinoidea: Holopodidae), Zootaxa 1717, pp. 31-38 : 32-33

Genus Holopus d’Orbigny, 1837

Type species: Holopus rangii d’Orbigny, 1837 , pp. 6–8, pl. 1, by monotypy.

Other species: Holopus alidis Bourseau et al., 1991 ; H. mikihe new species; H. spileccense (Schlüter, 1878) .

Diagnosis: (After Rasmussen, 1978, p. T838.) “Cup tubular, more or less irregular, commonly with radial ridges or rows of tubercles. Wall of cup very thick, radial cavity moderate. Upper edge more or less five-sided. Radial articular face[t] for arms rather large, sloping slightly outward. Interarticular ligament fossae large. Radials and arms different in size, more or less distinctly arranged as group of 3 larger arms and group of 2 smaller arms. Arms stout, strongly curved, each branch with up to 25 to 30 brachials forming spiral and meeting laterally as cover over ventral side of theca when retracted. Proximal 3 to 10 large secundibrachials are succeeded by distinctly smaller brachials. Some brachials may be irregular, often smaller and triangular to fit within cover. Orals large, triangular.”

Remarks: The Holopodidae includes only two genera, Holopus and Cyathidium Steenstrup, 1847 . In Cyathidium , the more cap-like crown includes arms that are greatly reduced in comparison with those of Holopus , and are not visible when enrolled ( Roux et al., 2002, pp. 808, 819). The reported divergent molecular signatures of Holopus and Cyathidium are considered to be an artifact, as was also suggested by Cohen et al. (2004). We recognize the close relationship of the two genera, as demonstrated by their numerous morphological similarities and distinctness from all other crinoid taxa ( Heinzeller et al., 1996).