The widespread sea hare species Aplysia parvula includes four genetically distinct lineages, containing a total of ten different species. While the four lineages can be differentiated by their external characteristics, species in each clade are often morphologically indistinguishable. A review of literature and type material revealed that several available names exist for species recognized herein: Aplysia parvula is retained for a species from the north-eastern Atlantic; A. atromarginata, A. elongata, A. nigrocincta and A. japonica are resurrected for species from the western Pacific Ocean, the Hawaiian Islands, the Indian and western Pacific Oceans, and Japan and Korea, respectively. Two new species names are introduced for animals from the eastern Pacific, and the Atlantic and Indian Oceans. Mitochondrial sequences from Mediterranean and eastern Atlantic specimens identified as A. parvula, resulted to be A. punctata. However, two specimens were heterozygotes of histone H3 alleles of A. punctata and of a new Atlantic species described herein, suggesting they could be hybrids. These results contradict the hypothesis that the Mediterranean was colonized by A. parvula. If an invasion occurred, it was a limited introgression of nDNA from an Atlantic species into native A. punctata populations.

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Valdés, Á . (2012). Molecular systematics of the 'Navanax aenigmaticus' species complex (Mollusca, Cephalaspidea): Coming full circle. -Zoologica Scripta, 41, 374-385. Molecular evidence from the mitochondrial COI and 16S genes and the nuclear H3 gene indicate that the traditionally recognized cephalaspidean sea slug species Navanax aenigmaticus consists of three deeply divergent lineages with disjunct ranges in the eastern Pacific, western Atlantic and eastern Atlantic. Each of these allopatric lineages is highly variable in colour and body size, which hampers identification of some possible consistent differences between them. Some conchological differences between the three lineages seem to be correlated with the groupings resulting from the analyses of molecular data, but the results of the morphological studies are inconclusive. Because of the presence of well-supported divergences and molecular synapomorphies, these lineages are herein considered to be three separate cryptic species. A review of the literature and available type material was conducted to determine the valid name for each of the three species. In other to promote nomenclatural stability, the oldest name with a description that allows a positive identification was selected over older, taxonomically ambiguous names. The conclusion of this revision is that the valid names for the species are Navanax nyanyanus (Edmunds 1968)eastern Atlantic, Navanax gemmatus (Mö rch 1863) -western Atlantic and Navanax aenigmaticus (Bergh 1893) -eastern Pacific.

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