Mussel Features
Easy and accurate use of this guide relies on a familiarity with mussel shell features. The tabs below open to display images and descriptions of the most important of these, illustrating them with typical examples from metro area specimens. Most of our taxa are relatively easy to identify by careful use of these external features alone; for problematic taxa, a key to area species has been provided by the New Jersey Endangered and Nongame Species Program.
To aid in the conservation of living mussels, only the shell features are illustrated. Use of the soft tissues and internal organs, often used for accurate determination of genera, requires the death of the animal and its careful preservation. The killing of mussels for identification is strongly discouraged, as it is rarely required in our area to make an accurate determination. In addition, many of our species are legally protected by state and federal law. Careful observation, notetaking, photography, and examination of spent shells are recommended instead. For information on regulations governing the collection of mussel specimens or spent shells, please go to: Permits
The anterior is the shorter end of the shell as measured from the beak. In species with a long, elliptical or "narrow" shape the anterior end should always be evident.
In those species that are rhomboidal or "rounder" in shape, such as Leptodea ochracea, the shorter end may not be apparent at first. Typically, the end where the growth lines are farthest from the beak is the posterior (see image left).
Shell shape is among the external features most useful for identification. The types of shapes are described by their resemblance to geometric figures. These descriptions are broadly accurate, although the shape of a species may vary, and some species are more plastic in their shape than others.
It is often useful to examine a series of shells or specimens in order to accurately gauge a species' range of variation.
A term such as "sub-ovate" may apply to species that share variations of this general shape. Thus L. cariosa and L. radiata (left) share an ovoid form that is modified by a distinct "flattening" of the posterior shell margin- hence "sub-ovate", an oval shape appearing to be flattened on one side.
Note that a "triangular" shape, as in A. heterodon (above), refers to the slope of the shell margin on the anterior side.
Compare the modification and variation of the elliptical shape in A. implicata and M. margaritifera (left) with that of the subovate shape in L. radiata (above). Also carefully compare the sub-elliptical shape of M. margaritifera with the rhomboid shape of A. heterodon
Note: In temperate latitudes such as the metro region growth lines are laid down annually. Complete growth lines may thus be counted to approximate mussel age.