Did anybody see which way January went??  Talk about warp-speed time
travel!!
 
        A week or so ago, someone asked about the  feature i admire the most
about Mollusc shells: the incredible range of variation many populations
exhibit, regarding color and patterns, especially in many of the most
common spp, and the most successful and diverse families, such as
Pectinidae,  Neritidae, and of course Conidae.  It is highly probale
that these spp and families BECAME so successful because of their
adaptability, which included their ability to blend in with their
visible surroundings whenever nessessary -ie, whenever predatory
pressure based upon color and/or pattern occurs.  I believe that many
spp maintain a genetic "pool"
of visually-related variation, based partly upon past episodes of
visual predation which enhanced the relative survival rate of certain
colors and pattern-types, and partly upon simple genetic drift, which
often produces morphs of limited or no survival value (as in shocking
orange Nucella lapillus L., or violet Neptunea lyrata decemcostata-
beautiful from our perspective, but not corresponding  to any feature in
their environment that i have ever seen!).  The more varied a given
species' pool of visual possibilities, the better their chances of
surviving  in different portions of their total niche, if and when
visual predation becomes intense locally or regionally.
A "local" example would be Littorina obtusata L.. In situations where
crabs can easily pick them off their Fucus habitat, they are
marvellously camoflaged, being mainly green and pale yellow, these
being  the colors of the blades and bladders of the algae they live on.
In other localities, where crabs are less able to get at them, they are
orange, black-striped, and a good variety of morphs or  quite scarce in
the crab-harrased populations.
        Some of the variation we humans easily notice in sunlight, with eyes
capable of differentiating  many thousands of colors, hues, and pattern
subteties, may be due to the differing  visual charactaristics of the
bakground,  the medium (air vs water of varying  depth)  the shell is
viewed in, as well as the visual capabilities of the relevant
predator(s):  Water  filters out certain wavelengths, and most marine
predators cannot distinguish as wide a range of colors as we can- some
indeed are color-blind, and rely upon form, pattern, refleciveness,
etc., to discern their lunches from  surrounding  inedible materials.
So, what may look like very different colors and hues to our discerning
eyes, may be nearly identical to the predator(s) which help determine
their relative frequencies  by eating  the inhabitants of the shells
they can more easily find.  Likewise, some patterns may be just as
difficult for predators to discern as others which seem to us, under
very different circumstances, to be radically dissimilar (Neritidae
would seem to be masters at producing "visually-equivilant" patterns!!).
        Any other  theories, or comments and critisisms  on the ideas above,
would be most welcome!                                  -Ross Mayhew
(Schooner Specimen Theories)