What are the morphological (physical) differences between the two species?
The two species can be differentiated by morphological differences of the shell. The zebra mussel has a definite angle, or carina, between the ventral and dorsal surfaces, whereas, the quagga has a rounded carina (May and Marsden, 1992). The ventral side of the shell of zebra mussels is flattened, but the quagga has a convex ventral side. This can sometimes be distinguished by placing shells on their ventral side; a zebra mussel will remain upright whereas a quagga mussel will topple over (Claudi and Mackie, 1994). Overall, quaggas are rounder in shape and zebras are more triangular. The quagga mussel also has a small byssal groove on the ventral side near the hinge and the zebra mussel has a larger groove in the middle of the ventral side. Color patterns vary widely with black, cream, or white bands; a distinct quagga morph has been found that is pale or completely white in Lake Erie (Marsden et al., 1996).
