Phylogenetic systematics of the genus Platydoris (Mollusca, Nudibranchia, Doridoidea) with descriptions of six new species

Abstract

The genus Platydoris Bergh, 1877 is characterized by a flat body, wide mantle margin, and elevated branchial and rhinophoral sheaths. Examination of a number of specimens and a review of the literature have shown that there are at least 20 valid species of the genus Platydoris world-wide. Some of them have previously been described by other authors and are redescribed or discussed here: P. argo, P. scabra, P. cruenta, P. angustipes, P. ellioti, P. formosa, P. inframaculata, P. pulchra, P. sanguinea, P. townsendi, P. capricornensis, P. esakii, P. macfarlandi, P. galbanus, P. carolynae. Six new species are described here: P. inornata, P. ocellata, P. annulata, P. sabulosa, P. cinereobranchiata, P. rolani. Platydoris tabulata is a nomen dubium. Species removed from Platydoris include: Doris hepatica, D. murrea, P. variegata, P. punctatella, P. papillata, P. spinalusa, P. carinata, P. immonda, P. spongilla, P. maculata, P. stomascuta. A phylogenetic analysis was conducted, showing the genus to be monophyletic. There was strong support for a clade of all species of Platydoris included in the analysis except for the nodes containing P. annulata and P. macfarlandi, which are found in deeper water than the rest of the genus. This major clade was further divided into a clade of Atlantic and Eastern Pacific species and a clade of Indo-Pacific species, showing a strong biogeographical trend. Important characters separating the clades include ventral pigment around the foot, large ventral spots, the presence of vaginal hooks, and whether the accessory gland enters the atrium on the side of the vagina, the side of the deferent duct, or between the two.