Taxonomic review of Kaloplocamus from the Yellow Sea, China with the description of a new species (Nudibranchia, Doridina, Polyceridae)

Species of Kaloplocamus Bergh, 1880 are enigmatic Nudibranchia sea slugs, and only two valid species are reported in the northwestern Pacific. Kaloplocamus japonicus (Bergh, 1880) was initially described based on alcohol-fixed specimens. In the latest revision of Kaloplocamus, it was synonymized with Kaloplocamus ramosus (Cantraine, 1835). Recently, several nudibranchs were collected from Tianheng, Shandong Province, China, and one of them is identified as an undescribed species described here as Kaloplocamus albopunctatus sp. nov. based on integrated approaches incorporating morphological observations, internal anatomy, and phylogenetic analyses of two mitochondrial (COI, 16S rRNA) genes. The other species is identified as K. japonicus Bergh, 1880 based on the anatomy of the reproductive system. The new species K. albopunctatus sp. nov. is similar to K. ramosus in having a bright orange-red color pattern but differs significantly in the structure of appendages and reproductive system. Kaloplocamus japonicus can be easily distinguished from other Kaloplocamus species by its translucent, white-pink coloration and unique features of the female reproductive organ. Both species are supported as distinct species in all molecular analyses. The phylogenetic analyses propose a new estimate of the relationship between Kaloplocamus and Plocamopherus, and the evolution of bioluminescence within Triophinae is discussed. Our results also suggest cryptic biodiversity within the K. ramosus species complex.