Description of three new species of Tambja (Gastropoda, Nudibranchia, Polyceridae) from the western Pacific Ocean reveals morphological characters with taxonomic and phylogenetic significance for traditional Polyceridae and related ‘phaneorobranch’ nudibranchs

Three new species of Tambja Burn, 1962 (Nudibranchia, Polyceridae, Nembrothinae) are described and illustrated, and two new genera are introduced. Tambja dracomus spec. nov. occurs in (cool temperate) southeastern Australian and northern New Zealand waters; T. caeruleocirrus spec. nov. occurs more widely in (warm temperate) southwestern Pacific waters with its distribution centered in eastern Australia; T. pulcherrima spec. nov. occurs very widely throughout the (tropical, subtropical and warm temperate) western Pacific Ocean from southern Japan to northern New Zealand. The fact that there is no remaining type series of Nembrotha (?) verconis Basedow & Hedley, 1905 (presently Tambja verconis) is taxonomically significant, not only because it is the type species of the genus Tambja, but also because that species must be distinguished unequivocally from one of the species newly named here, T. pulcherrima, which it resembles externally. To remedy this nomenclatural gap, a neotype is herein designated for Nembrotha (?) verconis Basedow & Hedley, 1905. These three new species and the investigated morphological characters they possess have important phylogenetic implications for the genus Tambja within the traditional family Polyceridae. This genus is presently an assemblage of at least two distinct clades. In particular, we suggest that all, not just some, species of Tambja sensu stricto possess a prerhinophoral sensory organ that is probably homologous with those possessed by (at least some) species of Thecacera and Gymnodorididae. Five small species lacking this organ and constituting a clade genetically are here shifted out of Tambja into Martadoris gen. nov., thus rendering Tambja monophyletic. Neither is another traditional nembrothine genus, Roboastra Bergh, 1877, monophyletic. On account of rows of sensory pits all along the body (none being homologous with the prerhinophoral sensory organ) we suggest Roboastra sensu stricto should accommodate only the type species, the relatively small R. gracilis (Bergh, 1877). The large species that lack these pits and are predatory on other nembrothines previously classified in Roboastra are herein shifted into Tyrannodoris gen. nov.