© The Norwegian Academy of Science and Letters • Zoologica Scripta, 31, 3, July 2002, pp271–319 271 Dorgan, K. M., Valdés, Á. & Gosliner, T. M. (2002). Phylogenetic systematics of the genus Platydoris (Mollusca, Nudibranchia, Doridoidea) with descriptions of six new species. — Zoologica Scripta, 31, 271– 319. The genus Platydoris Bergh, 1877 is characterized by a flat body, wide mantle margin, and ele- vated 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 re- described 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. spinulosa, 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. Kelly M. Dorgan & Terrence M. Gosliner, Department of Invertebrate Zoology and Geology, Cali- fornia Academy of Sciences, Golden Gate Park, San Francisco, CA 94118, USA. E-mail: tgosline@calacademy.org Ángel Valdés, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA. E-mail: avaldes@nhm.org Blackwell Science, Ltd Phylogenetic systematics of the genus Platydoris (Mollusca, Nudibranchia, Doridoidea) with descriptions of six new species KELLY M. DORGAN, ÁNGEL VALDÉS & TERRENCE M. GOSLINER Accepted: 2 January 2002 Introduction The genus Platydoris Bergh, 1877 contains several generally large species of dorid nudibranchs, distributed throughout tropical and temperate areas in the Atlantic, Eastern Pacific and Indo-Pacific. Species of Platydoris are easily recognized by their flattened, normally rigid (or coriaceous) body. This genus is also characterized by the dorsum covered with very small caryophyllidia (Foale & Willan 1987), a generally lobate branchial sheath, a non-tubular prostate with two different portions, a penis (and in some cases a vagina) armed with hooks, a lobate accessory gland, a smooth labial cuticle, and hamate radular teeth (Bergh 1877a; Valdés & Gosliner 2001). Species of Platydoris are mostly found in shallow waters, but some species have been described from deep waters (e.g. P. macfarlandi, P. annulata). A review of the literature reveals that most species of Platydoris are poorly described and are either unidentifiable or synonyms of other species of this or other genera. This paper attempts to review the taxonomic status of the described species of Platydoris, based on a re-examination of available type material and the original description of each species. In addition, six new species from the tropical Atlantic and Indo-Pacific are described, and 11 species are re-described. Platydoris was recently shown to be monophyletic, and closely related to Baptodoris Bergh, 1884 and Gargamella Bergh, 1894 (Garovoy et al. 1999; Valdés & Gosliner 2001). However, the phylogenetic relationships within the members of Platydoris were unknown. This paper examines the phylog- eny of the species of Platydoris. Materials and methods The studied specimens are deposited at the Department of Invertebrate Zoology of the California Academy of Sciences (CASIZ). Type specimens of several species were obtained