Re: antiquity of segmentation

[Joseph Murakami <jymurakami@xxxxxxx>]

Bill Shear wrote:
> 
> The radial symmetry of echinoderms is clearly secondary, based on their
> ontogeny, and if one accepts carpoids, etc., as early echinoderms, perhaps
> on the phylogeny of adults as well.  Interesting that many living taxa of
> echinoderms now seem to be imposing secondary (tertiary?) bilateral
> symmetry on the pentamerous radial symmetry--as in biscuit urchins and many
> sea cukes.
> 
> My reason for asking about the segmentation genes in echinoderms was of
> course the usual postulate that echinoderms and hemichordates are close to
> chordates (of course there is the proposal of Jeffries that the
> 'calcichordates' are the common ancestor of both groups).
> 
> If these genes do not occur in echinoderms or have a different function......
> 
> My understanding has always been that the three-part coelom found in
> deuterostomes and in some pseudocoelomates was not the same thing as
> segmentation.  The referenced article in Science last week points out that
> the segmentation genes operate only in the anteriormost 8 or 10 chordate
> segments which form as coelomic pouches fromthe gut.  The more posterior
> segments form in blocks of mesoderm without coelomic components.
> 
> Bill Shear
> Department of Biology
> Hampden-Sydney College
> Hampden-Sydney VA 23943
> (804)223-6172
> FAX (804)223-6374
> email<bills@tiger.hsc.edu>

Not to get off the subject too much, but I came across Claus Nielsen's
ANIMAL EVOLUTION: Interrelation of the Living Phyla, chapter 48 on
Phylum Echinodermata pg 377-378 where he  makes a very convincing case
for debunking Jefferie's 1979 and 1986 case for the Calcichordata
question.  The "gill slit" issue of Cothurnocystis seems to be on the
wane.  Cited were Philips 1979, Ubagn 1975, and Jollie 1982 on the other
side of the issue from Jefferies.

My question is, can anyone tell me if I can find jefferie's '79 and '86
studies?  Would like to read first-hand his work, especially in lite of
the gene homolog insight.

Joseph Murakami MD