Taxonomy and DNA barcoding in genera Cavolinia and Diacavolinia from the Indian Ocean and Northwest Pacific Ocean

Some so-called circumglobal and/or circumpolar marine species are proved to be complexes of cryptic species with restricted distributions by molecular analyses. These phenomena imply that marine species diversity has been underestimated. In this study we use shell morphological characteristics together with mitochondrial COI and 16S rRNA gene sequences in order to study the taxonomy and to identify species of genera Cavolinia and Diacavolinia in family Cavoliniidae from the Indian Ocean and Northwest Pacific Ocean. Our results showed that the species delimitation of Diacavolinia is not supported by molecular analyses, those morphospecies (D. grayi, D. vanutrechti, D. pacifica, D. elegans, D. angulosa, etc.) with distinct morphology from northwestern Pacific are a single species, namely D. longirostris. The subdivision of subspecies and/or forms for C. uncinata could not be confirmed by DNA evidence. Phylogenetic analysis of COI revealed two independent geographical lineages for C. uncinata, C. globulosa and D. longirostris respectively, suggesting that these morphspecies may harbour cryptic diversity. Nuclear mitochondrial pseudogene sequences of COI were detected from most individuals of D. longirostris, which can affect the analysis of DNA barcoding.