Deep-sea cryptobranch dorid nudibranchs (Mollusca, Opisthobranchia) from the tropical West Pacific, with descriptions of two new genera and eighteen new species

The study of a large collection of cryptobranch dorid nudibranchs from deep waters in New Caledonia and the Philippines revealed the presence of Austrodods kerguelenensis (Bergh, 1884); 18 new species belonging to the genera Cadlina, Austrodoris, Geitodods, Discodoris, Peltodoris, Paradoris, Diaulula, Rostanga, Sclerodoris, Baptodoris and Dendrodoris, and two previously undescribed genera, Goslineria and Pharodoris, The anatomy of all these species, including the digestive, reproductive, and nervous system, are studied in detail. All these species are clearly distinguishable from other members of their genera. Most of the species have a pale, simple background coloration, and two of them lack eyes. Both characteristics seem to be adaptations to living in deep waters. Other deep-water Atlantic and Pacific species of dorid nudibranchs have similar adaptations. The two new genera are characterized by the presence of large copulatory spines, numerous flexible spines in Goslineria, and two solid, bifid spines in Pharodoris. No other cryptobranch dorid genera previously described have similar copulatory spines. Some of the species here described belong to genera previously reported from cold or temperate waters, such as Austrodoris, Cadlina and Diaulula. Most of the species belong to genera that are widespread in either cold, temperate or tropical waters (Rostanga, Paradoris, Geitodods and Baptodoris), and only two belong to exclusively tropical genera (Sclerodoris and Dendrodoris). Vicariant events and vertical dispersal could explain the processes of speciation and the origin of these deep-water species.