History of the chromodorid nudibranchs: Nomenclature, phylogenetics, biogeography and classification

Abstract

In this contribution I explore the evolutionary history of the chromodorid nudibranchs. I began with the current classification based on comprehensive morphological study, which included 17 genera, and 250+ species as a starting point. I extracted and sequenced DNA sequence for over 340 specimens representing 150 species. I conducted Bayesian phylogenetic analyses on each data set comprised of approximately 1 kb of two mitochondrial gene fragments, cytochrome oxidase 1 and 16s. Each dataset included different combinations of taxa depending on the specific question. My goals were to: (1) test the monophyly of the chromodorid nudibranchs, (2) test the monophyly of the chromodorid genera by including more than one species of each genus, (3) Include dense taxon sampling of at the specific level to break up long branches and best determine lineage membership, (4) include intraspecific sampling to test species boundaries, (5) sample from a wide geographic region to test biogeographic hypotheses (6) simultaneously test species boundaries and phylogeny and (7) use the resulting hypothesis of relationship to propose a new classification of the chromodorid nudibranchs that will serve as a foundation for further work. In this study the Chromodorididae sensu Rudman is not monophyletic. The monophyletic group Cadlina is not a chromodorid. It is the sister group to Aldisa. Cadlina cannot be a member of the chromodorid Glade without including many other dorids in that Glade as well. The chromodorid nudibranchs without Cadlina are monophyletic and most likely sister to the Actinocyclididae. Aside from Cadlina and Tyrinna, all but of the traditional chromodorid genera for which I had appropriate data to test monophyly, are either non-monophyletic, or render another genus paraphyletic. I present a new classification of the chromodorid nudibranchs based on lineages recovered in this phylogenetic analysis. The proposed classification uses generic names attached to type species as Glade names. This new chromodorid classification recognizes 14 generic lineages. At least 15 previously unrecognized lineages (cryptic species) and ten new species were discovered with detailed intraspecific sampling. Thoughtful and stepwise taxon sampling together with geographically diverse intraspecific sampling conducted at the same time as phylogeny reconstruction allowed the most thorough reconstruction of the evolutionary history of the chromodorid nudibranchs to date.