>Tom and David,
>
>According to an analysis of the data from 630 base pairs of DNA sequence
>for the cytochrome oxidase I (COI) gene that is close.  The Unionoidea and
>Unionidae are paraphyletic and it is hypothesized that the glochidium is
>the ancestral unionoid larval type (the glochidium is not necessarily
>paraphyletic however).  The Margaritiferidae, Mycetopodidae, Mutelidae, and
>Hyriidae were all supported as monophyletic.  The topology of the tree is
>thus: ((((Unionidae [excluding Coelatura], Margaritiferidae), Coelatura),
>(Mutelidae, Mycetopodidae)), Hyriidae).  Neotrigonia was used as the
>outgroup.

Damn cladists! There's more to it than a single gene for God's sake! When
they've looked at all the genes, get back to me. The trigonaceans may not
even be ancestral to the unionaceans, despite "conventional wisdom." The
Pachycardiids are probably the most closely related group, but they are all
extinct. The study you mentioned found Neotrigonia to be the most similar
among the groups used, but then they could only use living animals -
pachycardiids would never even enter into their database. It would be like
a DNA study of Nautiloids -- of course they would find the Coleoids the
closest because they have no Ammonoids to compare. It's a shoe-horn
approach to pop taxonomy. Damn cladists!





*****************************************
 G Thomas Watters, PhD
 Ohio Biological Survey &
 Aquatic Ecology Laboratory
 Ohio State University
 1315 Kinnear Road
 Columbus, OH 43212 USA
 v: 614-292-6170  f: 614-292-0181
******************************************

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