The tail tells the tale: taxonomy and biogeography of some Atlantic Chelidonura (Gastropoda: Cephalaspidea: Aglajidae) inferred from nuclear and mitochondrial gene data

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. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 1077–1095.