Mussel of the

Page last updated
1 February 2017

Mussel of the Month

The February 2017 Mussel of the Month is Pseudodontopsis euphraticus. Pseudodontopsis is a monotypic genus from the Tigris-Euphrates Basin in the Middle East.

Prisodontopsis euphraticus
USNM 86329. Tigris River, near Bagdad, Iraq (type of Monocondyloea rhomboidea Lea).

P. euphraticus has a big, good-looking shell, but we don’t know very much about the species. It’s distribution in the Fertile Crescent means shells turn up occasionally in the archaeological literature (e.g., Ridout-Sharpe, 2015). But, the biological classification of the genus Pseudodontopsis is a house of cards.

The species was originally described in the 19th century in the genus Unio. Because of its reduced hinge teeth, P. euphraticus was classified for a while as Pseudodon, Leguminaia, etc., until it got its own genus Pseudodontopsis. Kobelt (1913) gave a long bit of hand-waving to make the case that P. euphraticus (and the various synonyms that he described) was distinct from the other genera in the region, and the name Pseudodontopsis has stuck since then.

However, as we explained last month, monotypic genera often seem like a cop-out — a place-holder for species of unknown affinities. Pseudodontopsis is one of those genera.

Today, we classify Pseudodontopsis in the subfamily Gonideinae based on argumentation rather than data. Both Modell (1964) and Starobogatov (1970) classified Pseudodontopsis in a subfamily called Pseudodontinae,* along with other genera like Pseudodon, Leguminaia, and Microcondylaea. Lopes-Lima et al. (2017) recovered those three genera in a clade with Gonidea, and ipso facto we conclude the Pseudodontopsis also belongs in a clade with the Gonideinae. Unfortunately, the transitive property is not a good basis for phylogeny. What we know about the glochidia of P. euphraticus is consistent with this classification (Al-Mahdawi & Al-Dulaimi, 2009).**

* We’ll ignore for this post that Modell and Starobogatov classified the Pseudodontinae in the family Margaritiferidae!

** There was a brief, pre-cladistic period in the late 20th century when some Palearctic mussels (including Pseudodontopsis) in the Nearctic genus Pleurobema, but we digress.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONIDAE Rafinesque, 1820
Subfamily GONIDEINAE Ortmann, 1916

Genus Pseudodontopsis Kobelt, 1913

Species Pseudodontopsis euphraticus (Bourguignat, 1852)
[+ Monodondyloea rhomboidea Lea, 1859]

To find out more about Pseudodontopsis and its classification, check out:
  • Al-Mahdawi, M.M. & M.M.A. Al-Dulaimi. 2009. Reproductive behavior of freshwater clams Unio tigrids (Bou.) and Pseudodontopsis euphraticus (Bou.) in Al-Habbanyah Lake - Iraq. Marine Sciences Journal 15: 17 pp.
  • Kobelt, W. 1913. Iconographie der Land- und Süsswasser- Mollusken, mit vorzüglicher Berücksichtigung der europäischen noch nicht abgebildeten Arten von E.A. Rossmässler vol. 19.
  • Lopes-Lima et al. 2017. Phylogeny of the most species-rich freshwater bivalve family (Bivalvia: Unionida: Unionidae): Defining modern subfamilies and tribes. Molecular Phylogenetics and Evolution 106: 174-191.
  • Modell, H. 1964. Das natürliche System der Najaden. 3. Archiv für Molluskenkunde 93: 71-126.
  • Ridout-Sharpe, J. 2015. Changing lifestyles in the northern Levant: Late Epipalaeolithic and early Neolithic shells from Tell Abu Hureyra. [in] Malacological Studies from the Past and Present: A Special Volume in Honor of Henk K. Mienis. Quaternary International 390: 102-116.
  • Starobogatov, Ya.I. 1970. Fauna Mollyuskov i Zoogeograficheskoe Raionirovanie Kontinental’nykh Vodoemov Zemnogo Shara. [Fauna of molluscs and zoogeographic division of continental waterbodies of the globe.] Nauka, Leningrad. 372 pp.
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