Sequence divergence of mitochondrial DNA indicates cryptic biodiversity inOctopus vulgaris and supports the taxonomic distinctiveness of Octopus mimus (Cephalopoda : Octopodidae)

DNA sequence diversity of octopods was investigated using the mitochondrial cytochrome oxidase III gene (mtCOIII). DNA was obtained from ethanol- or f ormalin-fixed tissue of 15 specimens belonging to Octopus mimus Gould, 1852 , Octopus vulgaris Cuvier, 1797 and Scaeurgus unicirrhus d'Orbigny, 1840, f rom coastal waters of the Mediterranean (France), the southwestern Atlantic (Brazil), the Caribbean (Costa Rica) and the southeastern/tropical Pacific (north Chile/ Costa Pica). A 612 bp fragment of the mtCOIII gene was seque nced and aligned to the orthologous sequences available from northeastern P acific Octopus species. Possible phylogenetic relationships were reconstruc ted. The mtCOIII gene tree revealed two main clusters, one comprised O. rub escens, O. dofleini and O. californicus, while the other included all O. vu lgaris specimens, O. bimaculatus, O. bimaculoides and O. mimus. With one ex ception all South American haplotypes including O. bimaculatus and O. bimac uloides appeared as the sister group of the Mediterranean haplotype of O. v ulgaris, indicating that most of the South American O. vulgaris specimens i nvestigated would not belong to the recently redescribed species O. vulgari s restricted to the Mediterranean and eastern Atlantic. The treatment of O. mimus as a species distinct from Mediterranean O. vulgaris is supported by a high nucleotide divergence of 12.7%. Based on the mtCOIII gene tree the existence of cryptic species among O. vulgaris-like octopods is suggested.