The first molecular phylogeny of cladobranchian opisthobranchs (Mollusca, Gastropoda, Nudibranchia).

The first molecular phylogeny is presented for the highly diverse, opisthobranch molluscan Cladobranchia. This study, the most comprehensive for Cladobranchia to date, used new sequences of two mitochondrial and one nuclear genes for 95 specimens from 22 families and 38 genera with a species of Pleurobranchoidea as outgroup. Although our results do not resolve all the relationships within the Cladobranchia, there are significant findings that have implications for the systematics of the Cladobranchia. Cladobranchia represents a monophyletic group within the Nudibranchia with the exception of a clade containing species of Melibe. These species share a deletion of four codons in the COI gene that may account for their strong divergence from the remainder of the Cladobranchia. Bornellidae is the sister group to the rest of Cladobranchia, but this relationship is weakly supported. A series of well-supported clades within Cladobranchia show little structure as to their relationships to each other in the current analysis. The relationships of Tethys and Hancockidae to other Cladobranchia remain unresolved. Pseudobornella orientalis is here transferred to Dendronotus as D. orientalis. With this systematic change Bornellidae and Dendronotidae are now monophyletic. Lomanotus appears as the sister group to a monophyletic Aeolidida, but this relationship is not strongly supported. Scyllaeidae is monophyletic in this study with Scyllaea being sister taxon to Notobryon. The Proctonotidae are monophyletic and are clearly nested in the Cladobranchia. Dotoidae is monophyletic when Pinufius is included in this clade. Doriodomorpha is sister taxon to the Arminidae. Within Arminidae, Dermatobranchus and Armina, as they are presently constructed, are not monophyletic. There is an interesting potential sister group relationship between Dirona albolineata and Lemina millecra that requires additional exploration with expanded taxon sampling. In this study, Marianina rosea is nested within Tritoniidae, thus we consider Aranucidae, and its synonym Marianinidae, as a junior synonym of Tritoniidae to preserve the monophyly of Tritoniidae. Copyright 2010 Elsevier Inc. All rights reserved.