>Date:    Thu, 25 Jun 1998 19:54:18 -0700
>From:    Scott E Jordan <[log in to unmask]>
>Subject: sexual dimorphism
>
>This is a topic that I have found myself wondering about before.  I don't
>believe that I have ever seen distinctions made indicating morphological
>differences between the shells of a molluscan specie's male and female.  It
>is certainly common amoungst chordates.  Anyone out there who can enlighten
>us on instances in the molluscan fauna?
>
>Scott Jordan
 
>Date:    Thu, 25 Jun 1998 23:39:19 -0400
>From:    mark <[log in to unmask]>
>Subject: Re: sexual dimorphism
>
>Good question, in the case of fresh water mussels (unionidae) the male
>shells are generally fatter then the females. This seems to be typical in
>most fresh water bivalves. Mark James Bethke
 
Mark,
 
This is a bit of an over simplification.  First, most unionids (or Hyriids,
Mutelids, Mycetopodids, and Etheriids, for that matter) are not obviously
sexually dimorphic.  Most of the dimorphic species are are members of the
unionid subfamily Lampsilinae (if this is really a monopyletic subfamily).
The vast majority of Anodontines and Amblemines are not dimorphic.  As for
males being "fatter" than females, I would say that the opposite is true.
Most females have a post basal expansion and are more inflated than males
in order to provide room for the eggs and glochidia.
 
Kevin
 
Kevin S. Cummings
Illinois Natural History Survey
607 E. Peabody Drive
Champaign, IL 61820
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http://www.inhs.uiuc.edu/cbd/collections/mollusk.html