Connected across the ocean: taxonomy and biogeography of deep-water Nudibranchia from the Northwest Pacific reveal trans-Pacific links and two undescribed species

In this paper, we investigate a collection of Northwest Pacific nudibranch molluscs by means of integrative taxonomy, including morphological analyses, molecular data from the cytochrome c oxidase subunit I, 16S rRNA, histone H3, 28S rRNA, 18S rRNA markers, and ecological data. Two new species, Bathydoris antoni sp. nov. and Dendronotus kurilensis sp. nov., are described, and their phylogenetic relationships reconstructed. We also document two potentially new species of the genera Cadlina (Cadlinidae) and Cuthona (Fionidae s.l.). For the first time, we report molecular data for the Northwest Pacific specimens of Colga pacifica (Polyceridae), Dendronotus patricki (Dendronotidae), Ziminella vrijenhoeki (Paracoryphellidae), and Zeusia herculea (Aeolidiidae). Our molecular data supports the existence of biogeographic connections between the shallow water nudibranch fauna and their continental slope counterparts and communities on both sides of the North Pacific with possible ongoing gene exchange between fauna of both regions. We found two general types of deep shelf and bathyal communities inhabited by nudibranchs in the Northwest Pacific, each characterized by a certain type of fauna and a connectivity with different bathymetric and geographic areas.