Environmental and taxonomic variation in fingernail clam (Bivalvia: Pisidiidae) shell morphology

Abstract

Variation in the shell morphology of Sphaerium and Musculium fingernail clams was examined using multivariate statistical techniques. On the basis of shell measurements alone, clams from either genera which were collected in running-water habitats could be distinguished, with over 90% accuracy, from clams inhabiting standing water. The discrimination between the two groups was mainly due to the greater size and thickness of shells from clams living in running water. The pisidiid genera Sphaerium and Musculium were also morphologically distinguishable, mainly by size. Morphometric classification of these groups also resulted in over a 90% success rate. The morphometric variation within each of the above groups was further compared using a principal components analysis of each group's morphometric correlation matrix. This analysis revealed differences in growth-related changes in form between the pairs of habitat and generic groups studied. The techniques used to compare ecologically or taxonomically distinct shells appear to be promising for use in either biological monitoring or habitat selection studies.