Die Gattung Bathydoris Bergh, 1884 (Gnathodoridacea) im phylogenetischen System der Nudibranchia (Opisthobranchia, Gastropoda)

Phylogenetic systematics of "Bathydoris" s.l. Bergh, 1884 (Mollusca, Nudibranchia), with the description of a new species from New Caledonian deep waters

There are six valid species in the traditional genus Bathydoris, all of them found in polar or deep waters: Bathydoris abyssorum Bergh, 1884 (from the deep equatorial Pacific Ocean), Bathydoris ingolfiana Bergh, 1899 (from Greenland), Bathydoris hodgsoni Eliot, 1907 (from Antarctic and subantarctic waters), Bathydoris clavigera Thiele, 1912 (from the Argentinean deep-sea basin and Antarctica), Bathydoris aioca Ev. Marcus and Er. Marcus, 1962 (from deep waters off California), and a new species, Bathydoris spiralis (from deep waters off New Caledonia). Bathydoris patagonica Kaiser, 1980 and Bathydoris violacea Baranets, 1993 are regarded as synonyms of B. hodgsoni and B. clavigera, respectively. Bathydoris spiralis is clearly distinguishable from other members of the genus mainly in having a triaulic reproductive system and a very elongated, spirally coiled deferent duct. Examination of the holotype of B. violacea revealed that it is a synonym of B. clavigera. Bathydoris vitjazi Minichev, 1969 is most likely a synonym of B. hodgsoni, but is provisionally regarded as nomen dubium until more material becomes available. The phylogenetic hypothesis supports the monophyly of the Anthobranchia but shows that the genus Bathydoris is paraphyletic. Species of Bathydoris are divided into two clades, one of them also containing the phanerobranch and cryptobranch dorids. Bathydoris type species B. abyssorum retains its name and diagnosis, but B. clavigera and B. spiralis are excluded from this genus. They are, however, provisionally maintained in "Bathydoris" s.l., a likely paraphyletic group. This result shows some incongruities between the traditional nomenclatural system and phylogenetic systematics.

Chemical ecology of the Antarctic nudibranch Bathydoris hodgsoni Eliot, 1907: defensive role and origin of its natural products

A variety of Antarctic marine invertebrates contains secondary metabolites that may provide defense against potential predators. However, only in a few cases have tissues, extracts or isolated compounds of these invertebrates been tested against sympatric predators. The Antarctic nudibranch Bathydoris hodgsoni Eliot, 1907 contains hodgsonal, a compound only present in the external body (mantle tissues), which may protect the slugs from predators. To test this defensive hypothesis for hodgsonal, we carried out a series of experiments using the sympatric omnivorous seastar Odontaster validus Koehler, 1906 as a potential predator. Our experiments revealed that natural concentrations of hodgsonal elicit significant feeding deterrent responses in O. validus. Furthermore, hodgsonal is probably biosynthesized de novo by the nudibranch, since it was not detected in the viscera (as it should be in the case of a dietary compound), its concentration in the mantle (0.05-0.15% dry mass) is quite constant in individuals from different localities and depths, and its sequestration from a particular dietary source is unlikely because B. hodgsoni is an omnivorous feeder.