Cavalier-Smith, T.; Allsopp, M.T.E.P.; Chao, E.E.; Boury-Esnault, N.; Vacelet, J. (1996). Sponge phylogeny, animal monophyly, and the origin of the nervous system: 18S rRNA evidence. Canadian Journal of Zoology. 74 (11): 2031-2045.
426043
Cavalier-Smith, T.; Allsopp, M.T.E.P.; Chao, E.E.; Boury-Esnault, N.; Vacelet, J.
1996
Sponge phylogeny, animal monophyly, and the origin of the nervous system: 18S rRNA evidence
Canadian Journal of Zoology
74 (11): 2031-2045
Publication
Available for editors
We sequenccd 18SrRNA genes of a calcareous sponge, Clalhrina cerebrum. a demosponge, Axinella polypoides. and a zoanlhid cnidarian. Parazanthus axjnellae. Our phylogenetic analysis supports the monophyly of kingdom Animalia and confirms that choaooflagellate protozoans are their closest relatives. Sponges as a whole are monophyletic. but possibly paraphyletic; demosponges and hexactineilids form a monophyletic group of silicious
sponges. Our phylogenetic trees support a monophyletic origin of the nervous system in the Immediate common ancestor of Cnidaria and Ctenophora. They weakly suggest that animais with a nervous system may be more closely related to calcareous sponges than to silicious sponges; the nervous system might have originated in an early calcareous sponge.
Our trees confirm thal Myxozoa and Placozoa arc animais that arose by secondary loss of the nervous system. but suggest that Myxozoa may be sislers of, rather than derived from, Bilateria. Kingdom Animalia is divided inlo four Subkingdoms: Radiata (Porifera, Cnidaria. Placozoa, Ctenophora). Myxozoa, Mesozoa, and Bilateria. The 18S rRNA genes of Myxozoa evolved over twice as fast as in Radiata. Comparison with the fossil record reveals a brief 10-fold (or greater) aeceleration in the rate of rRNA evolution in early Bilateria followed by normal low rates for about 500 million years.
