Gymnodoris nigricolor Baba, 1960 (Mollusca, Nudibranchia, Polyceridae) is a species complex

Molecular and morphological data on the ecologically unique dorid nudibranch Gymnodoris nigricolor Baba, 1960, reveals it is a species complex comprised of at least four different species. Two specimens collected in New Caledonia match the original description of G. nigricolor from the main islands of Japan and are assigned to this species. Additional specimens from New Caledonia are morphologically and genetically distinct and are described herein as the new species G. boussionae n. sp. Moreover, three specimens collected in Okinawa, Japan, are superficially similar to the New Caledonia specimens assigned to G. nigricolor but are morphologically and genetically different, and therefore they are assigned to the new species G. nagoensis n. sp. described herein. Finally, a specimen from the Marshall Islands with sequences deposited in GenBank is also distinct and constitutes a fourth species in this complex.