PHYLOGENY OF CEPHALOPODS INFERRED FROM MITOCHONDRIAL-DNA SEQUENCES

Sequences of partial mitochondrial cytochrome oxidase III gene (533 bp ) were obtained for 17 species of cephalopods, 14 decapods, 2 octopods , and 1 vampyromorph. This study aimed to: (1) compare partial COII an d COIII amino acid sequences of three species of cephalopods with othe r invertebrates in terms of base composition and phylogenetic relation ships, Cephalopod sequences are closer to Katharina tunicata sequences than to Mytilus edulis (marine bivalve) and Albinuria turrita (terres trial gastropod); (2) investigate the phylogenetic relationships among cephalopods. Nucleotides as well as amino acid sequence variations of a COIII fragment were examined with parsimony and distance methods. O ur data confirm the monophyly of the Decapoda and of each family. A hi gh hierarchical rank for sepiolids, already suggested by other authors , appears justified. The order Sepioidea comprising five families shou ld be abandoned, with Spirula being excluded. The surprising position of Idiosepius as the sister group of some oegopsids and not of sepioid s or sepiolids is confirmed. Vampyroteu this is the sister group of oc topods. However, the data do not allow resolution of the phylogenetic relationships between the orders of Decapoda; consequently we suspect a rapid radiation. (C) 1997 Academic Press.