An Ostracode Commensal of an Ophiuroid and Other New Species of Pontocypria (Podocopida: Cypridacea)

Abstract

Pontocypria hendleri, new species, is a commensal of the ophiuroid, Ophioblenna antillensis Liitken, collected from a reef in Belize. Pontocypria calva, new species, and Pontocypria sp. B occur in trawl collections from the southwest Pacific and North Atlantic, respectively. Pontocypria helenae Maddocks, previously found on Antarctic asteroids, now has been collected apparently free-living at seven localities in the South Atlantic and South Pacific. The ostracode genus Pontocypria was established by Miiller (1894) for the freeliving, actively swimming, Mediterranean species P. spinosa, collected among calcareous algae and detritus of Posidonia. Maddocks (1968, 1979) reported three commensal species of Pontocypria: P. helenae on three species of Antarctic asteroids, P. humesi from a sponge in Madagascar, and P. sp. (hereafter called P. sp. A) on a spatangoid echinoid in the North Atlantic. The Challenger lectotype of P. meridionalis (Brady, 1880), collected near the Falkland Islands, also belongs to this genus (Maddocks, 1968). In 1985 Gordon Hendler discovered that one specimen of an ophiuroid collected in Belize was infested with an ostracode, Pontocypria hendleri, new species. Each of the ostracodes was clinging by one antennal hook to the external integument of the disk or an arm of the brittle star, in the same manner illustrated earlier for P. helenae (Maddocks, 1968, pl. 2, fig. 2). The skin of this brittle star, Ophioblenna antillensis Liitken, has abundant sieve-like spicules small enough to be ingested, but none of these spicules are visible in the gut of the ostracodes, nor is there other evidence of harm to the host. As in other species of Pontocypria, the mouthparts are weakly constructed and the gut contents unidentifiable. Maddocks (1968) suggested that these species might feed on the soft organic detritus trapped by mucus secretions of the host or even on the mucus itself. Dr. Hendler reported (letter of 9 March 1987) that "the slimy skin and other characteristics of Ophioblenna antillensis indicate that the species should be referred to the Ophiomyxidae rather than the Ophiacanthidae as heretofore presumed. Ostracods that require hosts with relatively thick, mucus-producing integument would more likely occur with ophiomyxids than with ophiuroids that have a relatively thin layer of tissue covering the skeletal plates." The deliberate nature of this association is supported by the inclusion of a young juvenile as well as adult ostracodes of both sexes. Because there is no evidence that this association is either harmful or beneficial to the host, it is here classified as commensal. Perhaps any mucus-secreting echinoderm can be infested, and we should hasten to search holothurians and crinoids to see whether they, too, harbor these ostracodes! So far, each new class of host echinoderm has yielded a different species of Pontocypria, suggesting some antiquity for this relationship. The eurybathyal, cosmopolitan distribution of this genus further indicates significant geologic age, although the weakly calcified valves are poor candidates for preservation and have not been recognized as fossils. Two additional new species of Pontocypria, either free-living or detached from their hosts, have turned up in some trawl samples and are described below.