Thanks David, I forgot to acknowledge you in my earlier Reply (somehow your
reply wasn't connected to the thread).  I thought that the Argonaut shell was
an egg case, and therefore solely female.  I need to do some more reading I
guess.
Nora Bryan
Calgary, Alberta
Canada
 
David Campbell wrote:
 
> >There has been quite a bit of discussion lately about identifying
> >juvenile molluscs, but can anyone tell me, are there any examples of
> >extant molluscs that exhibit noticeable sexual dimorphism.  I have never
> >seen any examples of this in the shell books that I currently have
> >access to.
>
> In a few taxa, the female shell stores the eggs in a specially developed
> part of the shell, e.g. Milneria and Thecalia (Carditidae).  In many
> unionids, the female is shorter but wider around the gills, where the young
> are brooded.  Subtle dimorphism in other carditids has been suggested to be
> sexual, but the papers I am familiar with were looking at fossils, making
> it difficult to be sure.
>
> Dwarf males are known in some bivalves, including a few Pholadoidea and
> Galeommatoidea.  Male argonauts are likewise much smaller than females.
>
> Many male cephalopods (including the argonaut) have a specially modified,
> long tentacle for sperm transfer, providing a fairly evident morphological
> difference.
>
> In protandrous hermaphrodites (i.e., they change sex as they get older),
> the little shells are usually male and the large ones females, but this is
> not exactly sexual dimorphism.
>
> David Campbell
>
> "Old Seashells"
>
> Department of Geological Sciences
> CB 3315 Mitchell Hall
> University of North Carolina at Chapel Hill
> Chapel Hill NC 27599-3315
> USA
>
> 919-962-0685
> FAX 919-966-4519
>
> "He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
> Gold Bug