Fingernail clams (Muscu1ium transversum) are dominant bottom-dwelling
animals in some waters of the midwest U.S. These organisms are key links in
food chains leading from nutrients in water and mud to fish and ducks which
are utilized by man. In the mid-1950’s, fingernail clams disappeared from a
100-mile section of the Illinois R., a tributary of the Mississippi R. Some
factor(s) in the river and/or sediment currently prevent clams from
recolonizing areas where they were formerly abundant. Recently, clams
developed shell deformities and died without reproducing. The greatest
mortality and highest incidence of shell deformities appeared in test
chambers containing the highest proportion of river water to well water. The
molluscan shell consists of CaCO3, and the tissue
concerned in its secretion is the mantle. The source of the carbonate is
probably from metabolic CO2 and the maintenance of
ionized Ca concentration in the mantle is controlled by carbonic anhydrase.
The Ca is stored in extracellular concentric spherical granules(0.6-5.5μm)
which represent a large amount of inertCa in the mantle. The purpose of this
investigation was to examine the role of raw river water and well water on
shell formation in the fingernail clam.
