Mussel of the

Page last updated
28 June 2019

Mussel of the Month

The October 2016 Mussel of the Month is Psorula rudis. Psorula is a genus of seven species from Central America.

[Since April 2019, we have moved this species and all the members of Psorula to the genus Psoronaias, following the results of Pfeiffer et al. (2019), and P. rudis has been synonymized with P. semigranosa based on the previous work of Goodrich & van der Schalie, 1937. — DLG]

Psorula rudis
USNM 84210. Rio Taxtunilha, Guatemala (type).

There is almost nothing to say about Psorula. It has been listed as a valid genus of the family Unionidae in checklists (Frierson, 1927; Haas, 1969; Graf & Cummings, 2007) and web pages (like this one and ITIS). Internet search results tend to be a bit inflated since Psorula is also a valid genus name for a fungus.

We suspect that the richness of the genus has been inflated by splitting. The genus is distributed in southern Mexico and Guatemala, but the endemic hotspot of the currently recognized species is the Rio Usumacinta. The seven species of Psorula are represented by only 48 specimen lots in the collections we have toured, and 30 of those belong to two species. As with other Mesoamerican freshwater mussel genera (e.g., Reticulatus), we have needed a revision for almost a century.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONDAE Rafinesque, 1820
Subfamily AMBLEMINAE Rafinesque, 1820
Tribe QUADRULINI Ihering, 1901

Genus Psorula Haas, 1930

Species Psorula rudis (Simpson, 1900)

To find out more about Psorula and Mesoamerican freshwater mussels:
  • Frierson, L.S. 1927. A Classified and Annotated Check List of the North American Naiades. Baylor University Press, Waco, Texas. 111 pp.
  • Graf, D.L. & K.S. Cummings. 2007. Review of the systematics and global diversity of freshwater mussel species (Bivalvia: Unionoida). Journal of Molluscan Studies 73: 291-314.
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich 88: 1-663.
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