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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Several western Atlantic species of Chelidonura have been described mainly based on differences in colour pattern. Sequence data from two mitochondrial [cytochrome oxidase I (COI), 16S] genes and a nuclear [histone 3 (H3)] gene have revealed that all colour forms previously recognized from across the Caribbean, Bahamas, and Bermuda belong to the same species, Chelidonura berolina. However, several specimens from the Bahamas are genetically and morphologically distinct and are herein described as a new species, Chelidonura normani sp. nov. Externally, C. normani can only be distinguished from C. berolina by the morphology of the posterior end of the body and not by colour pattern. Both C. berolina and C. normani are genetically and morphologically distinct from the eastern Atlantic species Chelidonura africana, but the split between C. berolina and C. normani predates the split between C. berolina and C. africana. All three species differ in their protoconch morphology, which suggests different developmental modes. Furthermore, all three species display a broad variation in colour pattern, which raises questions on the biological significance of colour in this group. The reasons for the divergence between C. berolina and C. normani remain unknown but could be related to the complex geological history of the western Atlantic.

Sequence data of nuclear and mitochondrial genes obtained from specimens of Philinopsis collected in the Bahamas revealed two genetically distinct groups. Further examination of the shell and male reproductive morphology revealed consistent anatomical differences between them, corroborating that they are distinct species. The two species also display consistent differences in external morphology and colour pattern that became evident only after the molecular information was analysed. A review of the literature suggests that one of the species is Philinopsis petra, a widespread species in the Caribbean and northern Brazil, whereas the other is described here as a new species. Although both are sympatric in the Bahamas, they appear to be ecologically analogous, suggesting that they might have speciated allopatrically. Thirteen specimens initially identified as Philinopsis petra and two specimens of P. pusa (Ev. Marcus & Er. Marcus, 1976) were used in this study (Table 1). Most specimens were collected at Stocking Island, Exumas, Bahamas (Fig. 1). Specimens were photographed alive, narcotized using a 1 M solution of MgCl 2 , and preserved in 70% ethanol. Two additional specimens were collected in Tobago and Martinique and preserved in 10% formalin. All the specimens examined are deposited at the Natural History Museum of Los Angeles County, USA (abbreviated LACM).

North Pacific specimens of Melanochlamys sea slugs were examined morphologically (including the male reproductive morphology, shell and external coloration) and were sequenced for three genes (mitochondrial COI and 16S and nuclear H3). Phylogenetic and species delimitation analyses were used to determine the evolutionary relationships and species diversity among the specimens examined. Both molecular and morphological data revealed an unexpected high level of cryptic diversity. At least four distinct species occur on the Northwestern Pacific. Melanochlamys ezoensis occurs in Russia and temperate and cold areas in Japan. Three additional undescribed species occur in Japan and/or South Korea. One of the undescribed species occurs both in South Korea and in Japan, but only in Tokyo Bay, suggesting that it could be non‐native in Japan. Two distinct species occur on the Northeastern Pacific coast; Melanochlamys diomedea is widespread from Southern California to Alaska, whereas M. ezoensis was found only in San Francisco Bay, suggesting a human‐mediated introduction. This is further supported by the absence of records of M. ezoensis in San Francisco prior to 2001. The species diversity of Melanochlamys in the Northwestern Pacific is much greater than in the Northeastern Pacific; it is hypothesized that differences in geographic and ocean current system complexity might account for different responses to glacial extinction and postglacial expansion.