Phylogenetic systematics of the genus (Mollusca: Heterobranchia: Sacoglossa: Caliphyllidae) from the Pacific and Indian oceans with descriptions of nine new species.

The genus Bergh, 1870 has been a model for the study of defensive strategies, including chemical defences, ceratal autotomy, and crypsis or aposematism. Specialization on different algae and diverse genital armatures also make a useful system for investigating speciation by host shift versus sexual selection. Here, we review the genus in the Pacific and Indian oceans using molecular and morphological data. Two mitochondrial genes ( and 16S) and one nuclear gene () were sequenced from 154 specimens, including representatives from the Atlantic Ocean. Bayesian and maximum likelihood analyses were used to generate phylogenetic hypotheses. Species delimitation analyses performed on sequences recovered 17 genetically distinct Pacific and Indian Ocean species of , 10 of which are new to science. Nine new species are named herein ( sp. nov., sp. nov., sp. nov., sp. nov., sp. nov., sp. nov., sp. nov., sp. nov., and sp. nov.). The 10th species, from the Red Sea, is not named due to the absence of internal anatomical data. These findings increase the species richness in by about two-thirds, and demonstrate that even conspicuous taxa harbour considerable cryptic diversity.