by Dr. Gary Rosenberg
Species are often patchy in distribution, and may not be found
everywhere throughout their ranges, often because of lack of
appropriate habitat in a given area. Many parts of the world
are still inadequately sampled for mollusks, and the true ranges
of some of the species are probably broader than currently realized.
For a surprising number of species, nothing is known about their
habitat other than the depths in which they have been collected.
Even the depths may not accurately reflect habitat, as depth
records are often based on dead-collected shells, which might
have been transported into depths different from those in which
the animal lived. Observations of living animals by shell collectors
can often generate valuable scientific information.
Some species are so distinctive
or constant in coloration and sculpture as to be instantly recognizable.
Others vary so greatly that seemingly no two specimens are alike,
and many hundreds or thousands must be examined to understand
the ranges of variation and features separating them from similar
species. In some cases, variation is under direct genetic control,
as is the case with the bright, variable color patterns of the
coquina (Donax variabilis). In other cases, coloration and even
sculpture vary with diet. For example, some ovulids (allied
cowries) incorporate in their shells pigments from the soft
corals on which they live and feed. Individuals on yellow coral
have yellow shells, but if transferred to a purple coral of
the same species, they start making purple shells. Each species
of mollusk varies in a different way, making generalizations
about coloration and sculpture difficult to find, but endlessly
fascinating to search for.
The above material
has been adapted from Dr. Rosenberg's The Encyclopedia of Seashells,
published by Robert Halt, Ltd., London, 1992.