The Thick shelled river mussel and the Freshwater pearl mussel are occasionally difficult to separate from each other. If only living mussels are at hand (observe that both species are rare and/or protected !) it is only possible to examine the outside morphology of the shells. The most evident difference is the shape of their radius. With two equally sized specimens it is simple to compare the radius by looking at each of the specimens from the dorsal view. The Thick shelled river mussel can be distinguished from the Freshwater pearl mussel by its larger radius (thickness) at the centre. Another feature that can be of certain help is to look at the Freshwater pearl mussels lower margin that usually is curved inwards, giving it the shape of a "kidney". Observe that the shells of each species, shown on the photos here, do not differ in this feature. Both species can have a curved lower margin, or in contrary, the curve of the lower margin of the Freshwater pearl mussel can also be less pronounced. In case you find dead shells from the two species; the different shape of the hinge-teeth is a distinct feature when separating the two species.
Freshwater pearl mussel dorsal view
Thick shelled river mussel dorsal view
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