Ophioscolex Müller & Troschel, 1842

Martynov, Alexander, 2010, Reassessment of the classification of the Ophiuroidea (Echinodermata), based on morphological characters. I. General character evaluation and delineation of the families Ophiomyxidae and Ophiacanthidae 2697, Zootaxa 2697, pp. 1-154 : 108-109

Genus Ophioscolex Müller & Troschel, 1842

Figures 3D–E; 4I, O; 17A–B; 27A–E; 54H–J; 71I; 75–76

Ophioscolex: Müller & Troschel, 1842: 84 , 109

Type species: Ophioscolex glacialis Müller & Troschel, 1842 , by monotypy

Diagnosis. The disk is covered with a thick skin layer, small scales visible within when dried. The radial shields are small, triangular, hardly conspicuous even in dried specimens. The adradial genital plate is poorly developed, slightly curved, elongated, tightly articulated with the radial shield. The abradial genital plate is short and externally slightly conspicuous. The articulation surface of the adradial genital plate is without elevation. The articulation surface of the radial shield has a well-defined elevation but lacks a distinct proximal groove. The genital slits are long and conspicuous, but genital plates border only the small distalmost part. The jaw bears several spiniform oral papillae, similar in shape to the small cluster of ventralmost teeth. A pair of long spiniform adoral shield papillae, approximately 3–4 times as long as the oral papillae, is present only in the type species of the genus. The half-jaws are elongated, low. The adradial sides of the half-jaws lack distal folds. The dental plate is small, entire or consisting of a few not-completely separated irregular plates, elongated, without folds (or with traces of fusion of the smaller plates) and with few rounded sockets, irregularly placed. The teeth are spiniform and few in number. All teeth are similar in shape. The oral shield varies in shape, with or without distinct distal lobe. The adoral shield parts are similar in size, being only slightly widened distally. The dorsal arm plates are only conspicuous in one species ( O. inermis ). The ventral arm plates are well-defined. The arm spine articulations are large, of the single-opening type, encircled by a low, perforated, elevated border. The sigmoidal fold is absent. The arm spines are relatively long, conical in most species when covered in skin, completely entire, but remarkably comprised from several rods. Distal segments without hooks or with somewhat hook-shaped spines. Tentacle scales are completely absent in some species, including the type, whereas others have a small oval or spiniform scale on the lateral arm plate. The vertebrae are not distinctly widened distally; the dorsal medial suture is well-defined. The articulation is zygospondylous. The podial basins are large.

Material studied. Ophioscolex glacialis Müller & Troschel, 1842 , ZMMU D-817, D-843, D-866, ca. 100 specimens ( Figs 3D–E; 4I, O; 17A–B; 27A–E; 54H–J); Ophiosyzygus disacanthus H.L. Clark, 1911 , ZMMU D-875, 1 specimen ( Figs 75–76)

Remarks. H.L. Clark (1911) described three monotypic genera of the family Ophiomyxidae bearing close external resemblance to the genus Ophioscolex s.str: Ophiocynodus , Ophiosyzygus and Ophioleptoplax . Only one taxon, the genus Ophiocynodus (with the type species O. corynetes H.L. Clark, 1911 ) has been evaluated ( Mortensen 1933b) and considered as synonym of the genus Ophioscolex . For Ophiosyzygus disacanthus H.L. Clark, 1911 a revised diagnosis has been suggested and the absence of the radial shields claimed in the first description was considered as incorrect ( Turner & Heyman 1995). A specimen of Ophiosyzygus disacanthus , closely similar to the first description and from the same geographical region (Asian Western Pacific) was examined in the present study both externally and internally ( Figs 75–76). Few very large arm spine articulations of the single-opening type, small triangular radial shields, very low jaws and a dental plate with few small rounded openings ( Figs 75D–H; 76D–J), are all features essentially similar to those in the type species of the genus Ophioscolex , O. glacialis ( Figs 3D–E; 4I, O; 17A–B; 54H–J). Externally these species are also very similar. Most species of Ophioscolex , like Ophiosyzygus disacanthus , also lack the adoral shield papillae. The only striking difference between O. disacanthus and O. glacialis , is the streptospondylous vertebral articulation in the former ( Figs 76B–C). Considering the great variability and an easy shift from strepto- to zygospondyly in different ophiuroid taxa, for instance within the genera Ophiacantha and Ophiocamax , this difference appears as non-generic. Ophiosyzygus , therefore, is very similar to of the genus Ophioscolex s.str., but pending a detailed revision of the latter they are not formally synonymyzed. The genus Ophioleptoplax has thin evident dorsal arm plates, and thus differs from most species of Ophioscolex s.str. (excluding O. inermis Mortensen, 1933 ). The apparent absence of the radial shields (H.L. Clark 1911) in Ophioleptoplax is doubtful. The genus needs further investigation.

Number of species: 7.