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.