PHYLOGENY OF DECAPOD CEPHALOPODS BASED ON PARTIAL 16S RDNA NUCLEOTIDE-SEQUENCES

Various systematic and phylogenetic relationships have been proposed f or extant decapod Cephalopods, based mainly on morphology and on the r are paleontological remains. Nucleotide sequence data from the 3' end of 16S rDNA gene were used as an alternative approach to morphology; t his gene portion having proved to be appropriate to test. divergences in other groups of assumed equivalent age The results from 27 Decapoda species allowed us to calculate phylogenetic trees by the neighbor jo ining and parsimony methods (Paup and Hennig86). The trees were submit ted to bootstrapping. The order Sepioidea, including the sepiids, sepi olids and spirulids, is not supported by molecular evidence. Sepiolids are clearly excluded from the order, and the position of the Spirulid ae needs further clarification. In oegopsids, the intrafamilial groupi ngs obtained by the molecular approach is in agreement with morphologi cal data. The unresolved phylogeny at the suprafamilial level might be the result of two different events : earlier divergence than the Ceno zoic, or unequal evolutionary rates among taxa having appeared either by successive emergence or by fast radiation. The 3' end of 16S rDNA g ene of cephalopods is a precious tool to analyze taxonomic relationshi ps at the intrafamilial level. A gene with a lower evolutionary rate, is necessary to establish higher taxa phylogeny.