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.

Donax variabilis


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.