subtrapezoidal
|
rhomboidal to subtriangular
|
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.
|
Elliptio complanata
eastern elliptio
|
Alasmidonta heterodon
dwarf wedgemussel
|
It is often useful to examine a
series of shells or specimens in
order to accurately gauge a
species' range of variation.
|
|
|
|
|
subovate
|
subovate
|
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.
|
Lampsilis cariosa
yellow lampmussel
|
Lampsilis radiata
eastern lampmussel
|
Note that a "triangular" shape, as
in A. heterodon (above), refers to
the slope of the shell margin on
the anterior side.
|
|
|
|
|
subelliptical
|
subelliptical
|
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 (above).
|
Anodonta implicata
alewife floater
|
Margaritifera margaritifera
eastern pearlshell
|
|
New York Metropolitan Region and New Jersey
Freshwater Mussel Identification Handbook
