[Taxacom] Evolution of molluscs and other invertebrates
kennethkinman at webtv.net
Fri Jul 10 09:57:06 CDT 2009
I don't recall a recent paper by Goloboff et al. being discussed
here (or anywhere else for that matter). It sounds very interesting!!!
There was a paper by Giribet et al, 2006 (in Proc. Natl. Acad.
Sci., if I recall correctly). It came up with a new molluscan clade
called Serialia, but also came up with some strange results (such as a
polyphyletic Gastropoda). I strongly suspect that Giribet's choice of
outgroups was flawed, because if some of those outgroups actually
evolved from molluscs, then they are actually ingroup taxa (and as I
have stated before, using ingroup taxa as outgroups totally screws up
your results, especially for molecular data).
In any case, I am not presently advocating removing Bivalvia from
Phylum Mollusca (I still think gastropods probably evolved directly from
bivalves). I will have to see what data (and outgroups) Goloboff et al.
used. They had the scaphopods splitting off first??? That sounds very
odd. I hope they didn't use annelids (or other worms) in their
outgroup. Anyway, I'll have to try to track down their paper.
Wasn't it here where someone just posted a link to the recent
Goloboff et al. genomic analysis indicating that molluscs were not a
monophyletic unit? The paper explained that scaphopods and bivalves came
off the tree sequentially, followed by some other miscellaneous
invertebrate phyla (presumably "worms"), and THEN came the clade that
comprised the remaining molluscan classes. That implies that the only
way to keep mollusca s.l. as a phylum is to either include those other
invertebrate groups in between, or remove and elevate scaphopods and
bivalves to become separate phyla. It's not that bivalves make the
remaining molluscs paraphyletic, it's that they're apparently not even
in the same phylum! I imagine that the prediction that molluscs will
"become a primary target for analysis" is probably true, but going in a
very different direction.
Doug Yanega Dept. of Entomology Entomology Research Museum
Univ. of California, Riverside, CA 92521-0314
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