Partial sequence of the 28S ribosomal RNA and the echinid taxonomy and phylogeny — Application to the Antarctic brooding schizasterids

Different parts of the echinid 28S rRNA molecule were explored in order to find out a variable domain likely to be useful for studying relatively short range phylogenetic distances. rRNA sequencing was carried out by reverse transcriptase elongation of the 5 ‘end-³²P-label led synthetic DNA primers in the presence of chain terminating dideoxinucleotides. Our results suggest that the D₂ variable domain is a region of the 28S rRNA able to give indications of the relative distances of species belonging to the same genus (Abatus and other antarctic schizasterids), in spite of some difficulties of interpretation. Tentative trees based on partial sequences of the D₂ domain of regular and irregular echinids are discussed.