Ophiocomella sexradia (Duncan, 1887)

Stöhr, Sabine, 2011, New records and new species of Ophiuroidea (Echinodermata) from Lifou, Loyalty Islands, New Caledonia, Zootaxa 3089, pp. 1-50 : 38

Ophiocomella sexradia (Duncan, 1887)

Figure 17 E–K

Material. Sta. 1410: 1 spm.

Remarks. This small specimen may easily be mistaken for Ophiocnida or Dougaloplus , both genera of Amphiuridae with spiny disk. Clark (1970) alluded briefly to the similarity between Dougaloplus and Ophiocomella when she suggested that Dougaloplus dividua ( Matsumoto, 1917) may be synonymous with O. sexradia , but she never followed up on that idea. I have not examined any Dougaloplus species, but Ophiocomella does not have the parallel-ridge arm spine articulation typical for Amphiuridae ( Martynov 2010a) , but a large rounded articulation that suggests it is correctly assigned to Ophiocomidae . Morphological similarity may thus be due to convergent evolution, but a revision of Dougaloplus is needed to decide. Unusual for ophiocomids, the spines on the distal arm are thorny and slightly hook-shaped, which may support the hypothesis of a close relationship between Ophiacanthidae and Ophiocomidae proposed by Martynov (2010b). The species is usually hexamerous and fissiparous, although specimens with seven and five arms have been reported ( Devaney 1970). Devaney (1974) suggested that O. sexradia may be a species complex due to its high morphological variability and wide geographical distribution, but no further investigations have yet been conducted to answer this question.

Distribution. Widely distributed across the Indo-Pacific, littoral to 15 m.

Figures

FIGURE 17. SEM images of Ophiocomidae. A, B, Ophiocoma erinaceus, dental plate; A, external, B, internal. C, D, Ophiocoma schoenleinii, dental plate; C, external, D, internal. E – K, Ophiocomella sexradia, F – H, J, large arm; E, dorsal aspect; F, dorsal arm proximal; G, dorsal arm distal; H, lateral arm; I, ventral aspect; J, ventral arm; K, small, regenerating arm. L, M, Ophiocoma pusilla, L, dorsal aspect; M, ventral aspect. Dental plates orientated with dorsal end up. Scale bars in millimetre.