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Unionoida cum Grano Salis |
Taxonomic Summary
 We currently recognize 842 species of freshwater mussels in six families, grouped into two superfamilies. The basis for our family-group level classification is our own phylogenetic analyses of molecular and morphological characters:
- Graf, D.L. & K.S. Cummings. 2006. Palaeoheterodont Diversity (Mollusca: Trigonioida + Unionoida): what we know and what we wish we knew about freshwater mussel evolution. Zoological Journal of the Linnean Society 148: 343-394.
More information about diagonistic characters as well as a detailed discussion of family-group level taxonomy and results from other analyses can be found in that publication. Our classification can be depicted with a cladogram as follows:
For four of the six families, where there is sufficient phylogenetic diversity, the families are divided among various subfamilies and tribes. Each of the families is discussed individually.
 The family-level diversity of freshwater mussels is partitioned as follows:
Follow the links to find information about the distribution of each family and to see a list of all included species and genera.
The Unionidae is by far the most diverse of the six families, and it is also the most widespread. Taxonomically, the Unionidae is also the most complicated. Recent phylogenetic analyses have been sufficient to demonstrate that the tradiational arrangement of subfamilies is unnatural. However, too few Old World species have been studied to propose a robust alternative. In the meantime, we have grouped many Old World genera into incertae sedis geographical assemblages. More information about the biogeographical patterns of the Unionidae (and other families) can be found in the Geographical Summary.
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