The Superfamilies: History of Freshwater Mussel Classification and the Problem of the Hyriidae
The interrelationships of the six families of freshwater mussels continue to be debated in the scientific literature. Historically, a single character, larval type, was applied to group all unionoids into two superfamilies. However, modern cladistic approaches analyzing many different characters has challenged that view.
 The traditional superfamilial classification of freshwater mussels was set down by Parodiz & Bonetto in 1963, and it remained dogma for nearly three decades. Their view was that the primary split among freshwater mussels was diagnosed by larval morphology. The mussels with glochidium-type larvae (Unionidae, Margaritiferidae & Hyriidae) were grouped as the Unionacea, while those with lasidium-type larvae were placed in the Mutelacea.
More recently, datasets derived from various combinations of morphological and molecular characters have been analyzed to explore interfamilial relationships of the Unionoida. That work has tested the traditional arrangement of the freshwater mussel families and supports a revision of the classification. Where the traditional and modern views differ significantly is in the position of the Hyriidae.
The best-supported family-level classification of the Unionoida still recognizes two superfamilies, and with the modern improvements to the International Code of Zoological Nomenclature and a better understanding of family-group synonymy, they are now: Unionoidea and Etherioidea. Based upon examination of all available characters — not just larval morphology — the Hyriidae is placed with the lasidium-bearing mussels in the Etherioidea.
Issues still remain to be resolved over the interrelationships of the freshwater mussel families. As new characters are employed and heretofore unconsidered taxa are analyzed, we expect this classification to be further refined.
The more diverse families are further subdivided into subfamilies and, in some cases, tribes. The subfamilial groups are best understood for the classification of the Unionidae of eastern North America, the most mussel-rich area of the world.
Reference Cited
- Parodiz, J.J., A.A. Bonetto. 1963. Taxonomy and zoogeographic relationships of the South American Naiades (Pelecypoda: Unionacea and Mutelacea). Malacologia 1: 179-214.
|
