Ophioplexa, Martynov, 2010

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 : 79

Ophioplexa gen. nov.

Diagnosis. The disk covered with numerous small, uniform scales covered by a thin skin layer, not evident when dried. The radial shield and adradial genital plate are small and externally inconspicuous. The articulation surface of the radial shield is distinctly excavated ventrally, distally with a groove. The abradial genital plate is absent. The genital slits are small. The oral frame bears numerous oral papillae similar in shape to the cluster of the ventralmost teeth (apical papillae). Several adoral shield papillae, which do not differ considerably from the oral papillae, are placed around the second tentacle pore. The jaws are slightly elongated. The adradial sides of the jaws distally bear a few sharp straight folds. The dental plate is large with rounded sockets and irregular folds. The teeth are spiniform and numerous, ventralmost teeth of similar shape. The dorsal and ventral arm plates are well developed. The arm spine articulations are compressed transversally. Some proximal articulations may have a distinct nerve opening. The sigmoidal fold is absent. The arm spines are hollow, relatively short and flattened, not hooked distally. The vertebrae are distinctly keeled and with zygospondylous articulation.

Etymology. Ophio - (after ophiuroid) and plexus (Latin, noun, feminine), braided, in current usage meaning also a complicated combination of elements in a system, in reference to an intricate relationship of the new genus combining traits of both ophiomyxids and ophiacanthids.

Remarks. (see also under Discussion below). The new genus shows some similarities to the genus Ophiocymbium in the presence of a poorly developed adradial genital plate and radial shield, but possesses several important differences. The genus Ophiocymbium has distinct block-shaped distal oral papillae as adult and few apical papillae, whereas Ophioplexa gen. nov. is characterized by numerous spiniform oral papillae, both proximally and distally. The numerous apical papillae of Ophioplexa gen. nov. are placed in a dense cluster, whereas Ophiocymbium has only a few apical papillae. The arm spine articulations of Ophioplexa gen. nov. are dorso-ventrally compressed with distinct nerve and muscle openings, whereas Ophiocymbium has a typical rounded muscle opening, but the nerve opening, if conspicuous, has a different appearance. The dental plate of Ophioplexa gen. nov. has a remarkable appearance, with a combination of several articulations and numerous small openings ( Fig. 55M–N), whereas the dental plate of Ophiocymbium has a few round openings and completely lacks articulation ( Fig. 12E–H).