Thanks Paul
I was aware that nautiloids retained sexual dimporphism, although I wasn't
aware of what it was.  I believe also that in the Paper Nautilus, the
shell is internal to the female only.
I was more thinking about other molluscs.  I know that some are
protandrous and change during their lifetime from male to female.  Are
there any gastropod or bivalves where the male shell is noticeably
different from the female shell?
 
Paul Monfils wrote:
 
> Hi Nora,
> The ancestors of those extinct fellows have kept up the practice.
> Sexual dimorphism is seen in the shells of Nautilus.  One sex (female
> I think) has a wider, somewhat angular shell aperture, while the other
> has a narrow, more straight-sided aperture.  There was a discussion of
> this topic on Conch-L some months back.
> Regards,
> Paul M.
> Rhode Island