> >For Paleoheterodonta, Hyriidae should be with Muteloidea rather than
> >Unionoidea.
>
> This can't be right. The Hyriidae, Margaritiferidae, and Unionidae all
> share the same larval type, a glochidium, which is vastly different from
> the alien-esque haustorial and lasidium larvae of the Mutelidae and
> Mycetopodidae, which are clearly related.

I believe the glochidium is considered paraphyletic relative to the
haustorial and lasidium larvae.  I.e., glochidial larvae are primitive for
the Unionoida.  After the evolution of glochidia, the group split.  Within
one branch, the other larval type developed.  I will check the relevant
references, however.

David Campbell