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Date:         Mon, 5 Oct 2009 20:33:16 -0400
Reply-To:     Conchologists List <CONCH-L@LISTSERV.UGA.EDU>
Sender:       Conchologists List <CONCH-L@LISTSERV.UGA.EDU>
From:         Paul Monfils <PaulCyp@COX.NET>
Subject:      Re: anomia simplex (jingle shells)
In-Reply-To:  <p06200702c6f00e7dc07c@[]>
Content-type: multipart/alternative;

Hi David,

Welcome aboard! Anomia simplex is one of my common local shells too, here in Rhode Island. One interesting fact, which you have no doubt observed, is that you find dozens of left (³upper²) valves on the beach for every right (³lower²) valve you see, presumably because the right valve remains stuck on the tough byssal stalk after the animal dies and is thereby unable to wash ashore. I see the same color distribution you do. I occasionally find very large specimens, up to 60 mm or more, but most are under 40 mm. Iıd say there is little doubt that the coloration is genetically determined. Environmental or nutritional differences would be difficult to support when you find all the color forms clustered together on one rock. The question of whether color differences have any survival value might be interesting to explore, but I donıt think the fact that such differences exist is valid reason to assume that there are any particular effects. Some traits seem to ³just be there², apparently neutral in terms of effect on survival potential, positive or negative. This seems particularly true of color and pattern, considering that (1) most predators of mollusks, at least the invertebrate ones, find their food primarily through scent, not sight; (2) in most brightly colored molluscan species, the shell in life is covered with a periostracum that obscures the colors and pattern (this is not true of Anomia of course); and (3) species exhibiting such bright colors and patterns are frequently found in deep water where there is minimal, or even zero, light penetration, which would negate any visual purpose for such colors and patterns. A number of hypotheses have been proposed to account for these observations, but such hypotheses are extremely difficult to test in a laboratory setting, so little supportive data has been produced.


Paul Monfils


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