[Taxacom] Mollusca, major subdivisions

Kenneth Kinman kennethkinman at webtv.net
Wed Mar 18 08:11:48 CDT 2009

I wrote:  And has ANYONE ever even tried a bivalve outgroup for
gastropods???  If I'm right, that could completely revolutionize the
systematics of gastropods.   

David Campbell responded:  Yes, plenty of analyses of gastropods include
bivalves among the outgroups.  No, it doesn't support the idea that
euthyneura is basal in Gastropoda; the archaegastropod grade is basal
and euthyneurans are derived in molecular and morphological analyses

Dear All,     
      Since he uses the phrase "among the outgroups", I suspect that
David means that when multiple outgroups are used, they sometimes throw
in a bivalve.  That doesn't test a bivalve-first hypothesis AT ALL,
because it swamps out the phylogenetic signal with a bunch of ingroups
assumed to be outgroups (notice that in my cladogram, gastropods are
paraphyletic with respect to all the remaining molluscan groups).  What
needs to be done is using one or more bivalves as an outgroup (not
watering it down with other molluscs).  Then see what gastropods come
out as basal.  That's what I mean by thinking "outside the box".        
          -----Ken Kinman

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