Gary,
 
Surprise! Your article is on Conch-Net already.
http://coa.acnatsci.org/conchnet/rose0397.html
 
 I quote it in entirety below.
 
Also could everyone remember that viruses specifically are not supposed to
be a topic for Conch-L.  I also quote Rule Number 3 from the Conch-L Rules
and Recommendations at:
 http://museum.nhm.uga.edu/CONCH-L/CONCH-Lrules.html
 
Go have a look as a refresher or if you have never seen them before. Amy has
created some clever little snail critters to adorn the page.
 
Rule 3. NO Off-Topic Postings:
 
A primary rule on any list is to respect the list's published subject by not
posting off-topic messages. This includes virus
warnings, which are usually out-of-date hoaxes. Remember, what is 'new' to
you may be old news to everyone else. Please
post off-topic messages to a more appropriate list or news group.
 
 
 
CONCHATENATIONS
 
                 WHY DO SHELLS HAVE THEIR
                                   C O L O R S?
 
                                   by Gary Rosenberg, ANSP
 
As a curator of a large shell collection, I am often asked why shells have
their colors. The most frequent form of the question
is, "Are those the natural colors?" I resist saying "No, we painted all 12
million specimens in our spare time," and explain that
the colors are indeed natural and are generally thought to serve as
camouflage. This answer satisfies most people, but usually
does not satisfy the experienced shell collector.
 
What about color in deep-sea shells never exposed to sunlight or in species
active only at night, or where the color is hidden
by thick periostracum or inside the valves and can be seen only when the
animal is dead? Clearly there is more than one
explanation for color in mollusks.
 
In broadest terms, explanations can be categorized as visual or non-visual.
In visual explanations, color serves either for
camouflage or communication. If the species involved have only black and
white vision, then degree of contrast, not color
itself, is what is important. Non-visual explanations say that color is
incidental -- it is an epiphenomenon. The color doesn't
have a function in itself, but is associated with some other function.
Asking why some shells have their color is like asking why
mammalian blood is red -- that happens to be the color of the pigment
hemoglobin when it is oxygenated.
 
Visual Explanations
 
In some cases, bright colors might serve to warn predators that a species is
poisonous or distasteful, examples among
mollusks being some nudibranchs and ovulids such as Cyphoma. Color is
probably not used for communication within
species in mollusks, except perhaps some cephalopods which have
well-developed image-forming eyes. With mollusks,
visual explanations of color usually invoke camouflage, which can be
achieved in several ways:
 
   1.Make pigments that match the background. Many excellent examples of
camouflage are found among land snails,
     which often blend in with leaf litter. But camouflage occurs even in
the deep sea. There's no sunlight, but some
     predators produce their own light. Thus pelagic deep sea fish are
black, merging with the void, but bottom dwelling
     organisms in the deep sea tend to blend in with the bottom. (This might
also involve not making pigment, if the
     substratum is white.)
 
   2.Take pigments from something eaten. For example, simnias on sea whips
take purple or yellow pigments from their
     hosts. A yellow simnia transplanted to a purple host will thereafter
deposit purple shell.
 
   3.Look different from conspecific neighbors. This would make it hard for
predators to form a search image and might
     explain the enormous variation in species like Donax variabilis and
Umbonium vestiarium. Both species burrow in sand
     at the edge of the intertidal zone where waves break, scattering them
like pebbles, and in both, almost the full range of
     variation in the species can be collected in a few handfuls.
 
   4.Use chromatophores to blend into the background. For example, the
cuttlefish Sepia, which does not have color
     vision, tries to match the contrast pattern of the background. It can
be misled in an aquarium by gravel of unusual
     colors.
 
 
 
Non-visual Explanations
 
   1.Result of crystal structure. Nacre in abalones is a good example. The
nacre is not seen when the animal is alive, and its
     color is incidental to its function.
 
   2.Metabolic waste products stored in the shell. This explanation is often
advanced, but there are no proven examples in
     mollusks. Why spend energy to get waste products into the mantle for
deposition in the shell instead of just excreting
     them? And if it were essential to get rid of waste products in this
way, then albino shells should die young of metabolic
     poisoning. Also, shell pigments that have been studied are the same
types of pigments made by other groups of
     organism.
 
   3.Temperature regulation. In some intertidal species, a light colored
shell might aid in preventing desiccation by keeping
     temperature lower. In subtidal species, ambient water temperature would
minimize any temperature effect of shell
     color.
 
   4.No predators so anything goes. First, few mollusk species lack
predators. Analysis of stomach contents of batfish and
     lobsters has shown that they'll eat almost mollusk they encounter.
Naticids and octopus are also omnivorous -- think
     how many species you've collected with drill holes in them. Look at the
percentage of shells that have repaired breaks,
     which are often the result of failed attempts at predation. Second, if
pigment has no function, it should just be lost,
     because it takes energy to produce: witness cave animals.
 
     Although molluscivory is widespread, many mollusk species have few
predators that use vision to find their prey. So
     why do so many shells have pigmented color patterns, especially inside
the shell or hidden by periostracum where it
     can't be seen?
 
   5.Pigment strengthens the shell--it serves a structural function. Color
patterns often align with spiral or axial sculpture.
     Sculpture, like corrugation in cardboard, strengthens shells against
predators such as crabs, and pigment might further
     strengthen it. Instead of producing and transporting a thicker shell,
it might be more energy efficient for mollusks to
     make pigments. Pigments might also impede propagation of a crack in the
shell. The structural explanation also works
     for color inside of shells. A good example is Mercenaria mercenaria
(the quahog or cherrystone clam). The purple
     inside the shell, hidden when the animal is alive, lies along the edges
of the shell, just where the big Busycon whelks are
     likely to attack. The pigment in Mercenaria presumably makes it harder
for Busycon to chip the shell. Under the
     structural explanation, albinos would be at a disadvantage, but it
wouldn't be fatal to all individuals. And cave animals,
     which generally don't face predation (or big waves), wouldn't need
pigment for structural reasons.
 
 
 
Mixing and matching
 
More than one explanation can apply to a species. Because each species has
different biological characteristics, it has to be
evaluated on its own merits. The explanation for one species might not apply
to another. For example, Busycon contrarium
(the Lightning Whelk) makes a color pattern when it is young, but stops
making it as it gets older. Maybe it no longer needs
camouflage against predators once it reaches a certain size (or maybe it
changes habitat?). Conus leopardus (the Leopard
Cone) has a thick periostracum which hides its color pattern. Large adults
stop making the pattern -- maybe the shell is thick
enough after a certain size that it doesn't need to be reinforced. And
Mercenaria doesn't make the purple color as a juvenile
-- maybe the juvenile shell is too thin to stop Busycon even if pigment is
built in, so the animal concentrates its energy on
growing till it reaches a size where the pigment make a difference. So far,
all these explanations are merely just-so-stories. It's
easy to concoct scenarios, but hard to test them. To start with, I'll need a
vise and a set of matched albino and normal
shells....
 
Thanks to Stanley Francis, Harry G. Lee, Russell Minton, G. T. Watters, and
other subscribers to Conch-L whose ideas
during online debate on Conch-L prompted me to write this column.
 
 
Department of Mollusks, The Academy of Natural Sciences, 1900 Benjamin,
Franklin Parkway, Philadelphia, PA 19103-1195; Email:
[log in to unmask]
 
 
 
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Lynn Scheu, Editor
American Conchologist and The Conch-Net
Conchologists of America
1222 Holsworth Lane, Louisville, KY 40222-6616
502/423-0469
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Those who don't do anything never make mistakes.
                          --Theodore de Banville