THE MITOCHONDRIAL-DNA MOLECULE OF THE HAGFISH (MYXINE GLUTINOSA) AND VERTEBRATE PHYLOGENY

The vertebrates are traditionally classified into two distinct groups, Agnatha (jawless vertebrates) and Gnathostomata (jawed vertebrates), Extant agnathans are represented by hagfishes (Myxiniformes) and lampr eys (Petromyzontiformes). frequently grouped together within the Cyclo stomata. Whereas the recognition of the Gnathostomata as a clade is co mmonly ac knowledged, a consensus has not been reached regarding wheth er or not Cyclostomata represents a clade. In the present study we hav e used newly established sequences of the protein-coding genes of the mitochondrial DNA molecule of the hagfish to explore agnathan and gnat hostome relationships. The phylogenetic analysis of Pisces, using echi noderms as outgroup, placed the hagfish as a sister group of Vertebrat a sensu stricto, i.e., the lamprey and the gnathostomes. The phylogene tic analysis of the Gnathostomata identified a basal divergence betwee n gnathostome fishes and a branch leading to birds and mammals, i.e., between ''Anamnia'' and Amniota. The lungfish has a basal position amo ng gnathostome fishes with the teleosts as the most recently evolving lineage, The findings portray a hitherto unrecognized polarity in the evolution of bony fishes. The presently established relationships are incompatible with previous molecular studies.