Identification of five species of Dendrodoris (Mollusca: Nudibranchia) from Japan, using DNA barcode and larval characters

Species of the genus Dendrodoris are defined as “radula-less” dorids (Nudibranchia: Doridina: Porostomata: Dendrodorididae). These sea slugs are colorful nudibranchs distributed across the world’s oceans. Because of color variations and anatomical similarities, species discrimination has been disputed in several Dendrodoris species. We determined the partial mitochondrial COI gene sequences and 18S rRNA gene sequences of five Dendrodoris species (D. arborescens, D. denisoni, D. guttata, D. nigra, and D. rubra) and Doriopsilla miniata in Japan to clarify the species identity of each dendrodorid species. We examined a total of 50 specimens from the intertidal zone at 10 sites in four regions along the Pacific coast of Japan. Partial COI gene sequences significantly differed among the six species. Although six partial 18S rRNA gene sequences were obtained for the six species, sequences differed little among species and did not clarify details of the Dendrodoris phylogeny. We also described the morphological features of veliger larvae of three Dendrodoris species. (D. arborescens, D. guttata, and D. rubra) The veligers of D. arborescens had a brown-pigmented, cup-shaped shell, and its foot was not retracted into the shell. In contrast, the veligers of D. guttata and D. rubra had a transparent, coiled shell with an operculum. Mean shell lengths of D. arborescens, D. rubra, and D. guttata were 171.5 ± 8.0, 172.8 ± 4.9, and 222.3 ± 15.2 μm, respectively. The present molecular analysis and larval characteristics indicated that each of the six species is a distinct species.