The Hypselodoris infucata,H. obscura and H. saintvincentius species complex (Mollusca,Nudibranchia, Chromodorididae), with remarks on the genus Brachychlanis Ehrenberg, 1831

The Indo-Pacific species Hypselodoris infucata (Rüppell and Leuckart, 1830) and Hypselodoris obscura (Stimpson, 1855) have been regarded as distinct by most authors. In this paper, numerous specimens with the colour pattern described for both H. infucata and H. obscura, and collected from localities comprising the geographic range of both nominal species, have been examined and anatomically studied. All specimens from south-east Australia, the type locality of H. obscura, consistently have a very long ejaculatory portion of the vas deferens, whereas in specimens collected from other Indo-Pacific localities this portion is very short. There are no other major morphological or anatomical differences between H. infucata and H. obscura. It is not clear whether H. obscura and H. infucata are different species, but since there is at least a consistent anatomical difference between them, they are provisionally regarded as distinct. The reproductive system, radula and external morphology are extremely variable among specimens of H. infucata. Specimens from Indo-Pacific localities other than south-east Australia, even those externally similar to H. obscura, belong to H. infucata. Hypselodoris saintvincentius Burn, 1962, which has been regarded as a synonym of H. infucata, is clearly distinguishable by the external coloration, reproductive system and radular morphology. Phylogenetic evidence indicates that H. saintvincentius is the sister species of H. infucata and H. obscura. A re-examination of the holotype of the uncertain species Brachychlanis pantherina Ehrenberg, 1831 revealed that it is conspecific with Hypselodoris infucata. Therefore, the name Brachychlanis Ehrenberg, 1831, which has not been used for more than 50 years, has preference over the widely used name, Hypselodoris Stimpson, 1855. In order to preserve nomenclatural stability invalidation of the name Brachychlanis is proposed.