Nucleic Acids Research, 1984, Vol. 12, No. 12 5101-5108
© 1984
MOLECULAR BIOLOGY |
Evolution of multicellular animals as deduced from SS rRNA sequences: a possible early emergence of the Mesozoa
Laboratory of Molecular Genetics, Department of Biology, Faculty of Science, Nagoya University Chikusa-ku, Nagoya 464, Japan
Received April 9, 1984. Revised May 30, 1984. Accepted May 30, 1984.
The nucleotide sequences of 5S rRNA from a mesozoan Dicyema misakiense and three metazoan species, i.e., an acorn-worm Sacaogloaeus howalevskii, a moss-animal Bugula neritina, and an octopus Octopus vulgaris have been determined. A phylogenic tree of multicellular animals has been constructed from 73 5S rRNA sequences available at present including those from the above four sequences. The tree suggests that the mesozoan is the most ancient multicellular animal identified so far, its emergence time being almost the same as that of flagellated or ciliated protozoans. The branching points of planarians and nematodes are a little later than that of the mesozoan but are clearly earlier than other metazoan groups including sponges and jellyfishes. Many metazoan groups seem to have diverged within a relatively short period.