Description of the First Roboastra Species (Nudibranchia, Polyceridae, Nembrothinae) from the Western Atlantic
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A new species of polycerid nudibranch of the genus Roboastra (Roboastra ricei sp. nov.) is described from its type locality off Florida; it is also known from North Carolina. The animal is dark yellow with numerous dark blue, almost black, small spots scattered on the notum and both sides of the body. The oral tentacles, the rhinophores, the posterior part of their rhinophore sheaths and the gill branches are dark blue at the tip, light blue in the middle, and yellow at their bases. The edge of the foot is also dark blue. Two other species of the genus, Roboastra europaea Garcia Gomez, 1985, and Roboastra caboverdensis Pola, Cervera and Gosliner, 2003, are known from the Eastern Atlantic Ocean, but have not been found in the Western Atlantic. Roboastra ricei appears as the sister taxa of the two Eastern Atlantic species, although this relationship is not well supported. This description brings the number of species of the genus to seven. The distinctive color pattern, differences in the radula and reproductive system and its geographical distribution characterize this species and clearly distinguish it from all other described species. Similarly, COI and 16S mitochondrial nucleotide sequences clearly distinguish this species as distinct from all other members of the clade. Based on morphological and molecular phylogenetic analyses, Tambja tentaculata Pola, Cervera and Gosliner, 2005, fits within the clade of Roboastra species. In order to maintain the monophyly of Roboastra, we transfer this species to Roboastra.