Sunday, April 13, 2008

New results on relationships of phyla

Paleoblog reports on a Science paper that contends relationships between some of the major animal phyla (body types).

Amongst other results are:
- hypothesising a clade of moulting animals (previously defined as Ecdysozoa;
- relating lophophorates (three small marine phyla) to annelids and molluscs
- molecular confirmation of the monophyly of molluscs;
- supporting velvet worms rather than tardigrades as closes phylum to arthropods;
- hypothesising a clade uniting annelids, brachiopods, nemerteans and phoronids (mainly small marine phyla);
- ctenophores (comb jellyfish) as the earliest diverging multicellular animal of existing phyla.

This last result I find most interesting - that ctenophores diverged earlier than sponges, which were arguably closest in broad morphology to the ediacarans that preceded the Cambrian era from which emerged modern phyla. This newly attributed status of the comb jellyfish has filtered through to reportage in the mainstream press.

The authors analyse about 40 Mb of "expressed sequencing tags" from 21 phyla, including 11 for which the data had not previously been available. This is a form of molecular (genetic) analysis.

The pedigree of the sources is good. I am not sufficiently knowledgeable about the science, so I can only report the findings. There's a lot to digest.

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