Dear Conch-Lers:
 
I have delayed joining this discussion waiting to see who would be the
first to report the most obvious example of molluscan sexual dimorphism.
But after a couple of days, no one has yet mentioned Argonauta argo Linne,
1758 (Paper Nautilus) or any of the other (very few) argonautids.  Below I
quote and paraphrase from the wonderful new Australian book MOLLUSCA, The
Southern Synthesis.
 
"Argonautids exhibit extreme sexual dimorphism in size.  The female are
large, reaching over 100 mm mantle length, while the males are minute, up
to 15mm mantle length, depending on the species."  There are a few other
anatomical differences that are not so obvious. 
 
The shell is a single-chambered egg case.  It provides protection and
flotation, and is the site of attachments for the eggs.  The adult animal
is not attached to the shell.
 
There was a time when no one had ever found a male, many considered the
argonauts parthenogenetic.  "In 1827 Stafano delle Chiaje discovered a
small body attached to a female argonaut.  He concluded it was a parasitic
worm."  After several other false conclusions,it was described as the true
male argonautid by Muller in 1853  
 
A couple of additional comments.
 
Several people have mentioned Lambis lambis, the slightly larger specimens
with the upturned fingers being the females, and the smaller ones with the
straight points being the males.  A very serious Filipino young man took
two shells and showed me how nicely this enabled them to fit together,
explaining as he did so - "You can see how much easier this makes it for
them to do what they want to do."
 
I have done a lot of collecting on the Pacific side of Panama.  Around 
Panama City we found quite a few Cypraea cervinetta.  There was an
occasional one that was fully mature but only 1/2 or less the size of the
big ones.  My first thought was that the small ones were males. A couple of
hundred miles north on Gobernadora Island, the reverse was true, the small
ones were much more common.  I have trouble explaining that in terms of
sexual dimorphism.  People called them dwarfs  but is merely a name, it
doesn't explain anything.  Could it be something in the environment or what
they eat; but, if that was true, wouldn't it affect all the specimens in an
area.  Are there such things as dwarfs in the molluscan world, and among
these dwarfs are there both females and males?   I am just raising the
questions, I certainly don't have the answers.          
 
Betty Jean, The Tall One 
 
Betty Jean Piech    
Hockessin DE,USA
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_@/-The more I learn, the more I realize how little I know.-\@_
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