Mussel of the

Page last updated
3 June 2019

Mussel of the Month

The July 2019 Mussel of the Month is Pseudunio homsensis. Pseudunio is a genus of three species from Mediterranean Europe and northern Africa.

MNHN. Nahr al Kabir [Al Ladhiqoyah, Syria] (type of Margaritana syriaca Pallary, 1929).

Pseudunio homsensis is a worthy Mussel of the Month for a couple reasons. Back in January, we discussed the recent revisions of the Margaritiferidae that resulted in Margaritifera sensu lato being split into four genera: Margaritifera s.s., Gibbosula, Cumberlandia, and Pseudunio (Lopes-Lima et al., 2018). The "old sense" of the Recent Margaritiferidae being composed of a single genus (i.e., Margaritifera) is actually relatively new. Smith (2001) called this mussel Pseudunio homsensis and split Margaritifera s.l. among three genera. These oscillations in genus richness demonstrate that the taxonomy is still unsettled.

Like most of the species of Gibbosula, P. homsensis had been classified in the Unionidae. In fact, the prevailing view seemed to be that this taxon was merely a subspecies: Potomida littoralis homsensis (Haas, 1940, 1969; Schütt, 1983). However, the presence of mantle-attachment scars provided morphological evidence to confirm its classification in the Margaritiferidae (Falkner, 1994; Smith, 2001).

One of the major challenges of keeping track of freshwater mussel taxonomy is its complex history. The International Code of Zoological Nomenclature and the Principle of Priority (among others) necessitates a method for documenting historical precedence. The MUSSEL Project Database on this web site is just the sort of tool for tracking this information. On this very page, there are links to the specimen in the figure above, to the nomimal species Margaritana syriaca (a junior synonym of P. homsensis), the species Pseudunio homsensis, and the genus Pseudunio. From those links, it is easy to browse or search for more information in the database.

For example, for any nominal species (like Margaritana syriaca), the MUSSELpdb provides infromation about where it was described, the valid species to which it is assigned, an image of the type (if available), and a history of name use in various publications.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820

Genus Pseudunio Haas, 1910

Species Pseudunio homsensis (Lea, 1865)
[+ Margaritana syriaca Pallary, 1929]

To find out more about Pseudunio and the Margaritiferidae, check out:
  • Falkner, G. 1994. Systematik vorderorientalischer Najaden als Vorstudie zur Bearbeitung archäologischer Funde. [in] M. Kokabi & J. Wahl, eds. Beiträge zur Archäozoologie und Prähistorischen Anthropologie 53: 135-162.
  • Haas, F. 1940. A tentative classification of the Palearctic unionids. Zoological Series of Field Museum of Natural History 24: 115-141.
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich 88: 1-663.
  • Lopes-Lima, M., I.N. Bolotov, V.T. Do, D.C. Aldridge, M.M. Fonseca et al. 2018.Expansion and systematics redefinition of the most threatened freshwater mussel family, the Margaritiferidae. Molecular Phylogenetics and Evolution 127: 98-118.
  • Schütt, H. 1983. Die Molluskenfauna der Süßwässer im Einzugsgebiet des Orontes unter Berücksichtigung benachbarter Flußsysteme. Archiv für Molluskenkunde 113(1/6): 17-91.
  • Smith, D.G. 2001. Systematics and distribution of the recent Margaritiferidae. pp. 33-49. [In] G. Bauer & K. Wächtler (eds.). Ecology and Evolution of the Freshwater Mussels Unionoida. Ecological Studies Vol. 145, Springer-Verlag, Berlin. 394 pp.
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