Ophiocoma L. Agassiz, 1835

Stöhr, Sabine, 2011, New records and new species of Ophiuroidea (Echinodermata) from Lifou, Loyalty Islands, New Caledonia, Zootaxa 3089, pp. 1-50 : 36-38

Genus Ophiocoma L. Agassiz, 1835

Figure 17 A–D, L, M

Remarks. Seven species of Ophiocoma were found at Lifou ( Table 2). Of these, O. macroplaca ( H.L. Clark, 1915) , O. doederleini de Loriol, 1899 and O. schoenleinii Müller & Troschel, 1842 are new records for New Caledonia. Benavides-Serrato & O'Hara (2008) showed that O. schoenleinii is a distinct species, separate from O. erinaceus , with which it had been synonymized before ( Devaney 1970). Therefore, previous records of O. erinaceus from New Caledonia may include specimens of O. schoenleinii and the distribution of both species cannot be assessed. These dark brown to black coloured species are distinguished by O. erinaceus having two tentacle scales and red tube feet (white in alcohol), whereas O. schoenleinii has a single tentacle scale and grey tube feet (alive as well as in alcohol).

The differences in the dental plates shown by Benavides-Serrato & O'Hara (2008) are confirmed here at a smaller size of 15–16 mm dd. The internal surface of the dental plate in O. erinaceus lacks the dorsalmost perforations at this size, which are already present in O. schoenleinii . As additional character to separate these and a third dark species, O. cynthiae Benavides-Serrato & O'Hara, 2008 , the authors suggested the extent of granules covering the ventral disk. In O. erinaceus , the granules are supposed to persist from the disk edge almost to the oral shields, in O. schoenleinii only as a wedge near the disk margin and in O. cynthiae they are absent (Benavides-Serrato & O’Hara 2008). In the Lifou material one specimen that clearly belongs to O. schoenleinii , according to all other characters, has a fully granulated disk, another shows a wedge extending to the oral shield. Some specimens of O. erinaceus on the other hand show a short wedge and specimens of 7 mm dd lack granules altogether, but in O. erinaceus disk granules first appear at a size of 7.5 mm dd ( Devaney 1970). One of the syntypes of O. erinaceus (ZMB Ech 921) that I have examined in the Museum für Naturkunde in Berlin lacks granules on the ventral interradius. This character may therefore be less reliable and size-dependent. However, it cannot be ruled out that the syntype series includes both species, which would require selection of a lectotype to stabilize the concept of O. erinaceus .

Several O. erinaceus were preserved in what must be their night colour pattern; light brown to beige, radiating lines on a dark brown dorsal disk, similar to that shown for O. erinaceus by O'Hara et al. (2004). Unfortunately, the collection notes do not record the time of preservation, but since collecting and preserving in the field went on until midnight it is highly likely that these animals were preserved at night. Hendler (1984) demonstrated colourchanges related to time of day in four species of Ophiocoma , in some of which the presence of photoreceptors was shown later ( Aizenberg et al. 2001). Nothing is known about the presence of calcitic microlenses in O. erinaceus .

Ophiocoma macroplaca is distinguished from other species in the scolopendrina -group of Ophiocoma and most importantly from O. scolopendrina ( Lamarck, 1816) by the presence of four spines on the third arm joint. In the Lifou specimens this character is rarely present on all arms in the same individual. As reviewed by Devaney (1970), this species has caused some taxonomic confusion, because the tiny holotype had few elongated granules or spinelets on the disk. In the Lifou specimens, the disk granules vary somewhat in size and shape. A specimen with 11 mm disk diameter has a dense covering of small round granules measuring about 100:130µm (width:height) intermingled with larger conical granules of 130:170 µm, while a specimen of 6 mm disk diameter has mostly low round granules and few, scattered, about twice as large, conical granules. Other specimens have mostly low round granules, with larger conical ones restricted to the disk margin. The Lifou specimens of O. scolopendrina have only low, round granules, about as high as wide, widely spaced. In addition, O. scolopendrina is restricted to the littoral zone ( Devaney 1970) and has at Lifou only once been collected deeper than 5 m, whereas O. macroplaca was not found shallower than 4 m and as deep as 150– 200m. One of the specimens of O. macroplaca is almost white, presumably night colouration.

Ophiocoma pusilla differs from other species of Ophiocoma by its small size and hollow arm spines, a character also found in Ophiacanthidae and in Ophiomastix ornata .

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.