Mussel of the

Page last updated
7 December 2015

Mussel of the Month

The December 2015 Mussel of the Month is Pronodularia japanensis. Pronodularia is a genus of two species restricted to Japan and Korea in the eastern Palearctic.

Pronodularia japanensis
BMNH 1965181. Japan. Hugh Cuming Coll'n. [type]

When we published our global checklist almost a decade ago (Graf & Cummings, 2007), we didn’t have any mussels classified in the genus Pronodularia. Our current recognition of this genus is based on the work of Takaki Kondo (2008) and his generic revision of the freshwater mussels of Japan.

The story of Pronodularia is a continuation of our serialization of The Tale of Inversidens (and that story is just one part of the epic saga, The Whoa of the Old World Generic Classification of Freshwater Mussels). In many places, our classification of Asian freshwater mussels is very similar to the mid-20th century system of Haas (1969), but this long stasis should not be regarded as evidence that the classification is settled. Rather, it is the result of neglect. But, things are starting to turn around (e.g., Pfeiffer & Graf, 2015). It is the Indotropics that have received the least recent attention, but the Palearctic mussels have seen a fair amount of revision over the last eight years.

The former Inversidens is now split into three genera: Inversidens, Inversiunio, and Pronodularia. As we explained last year at this time, Inversiunio was split from Inversidens to accommodate the fact that some species (like I. reinianus) have the hooked-type glochidia of the family Unioninae, while others have the unhooked-type glochidia of the Gonideinae.* This has happened with other traditional genera once their larvae became better understood (e.g., Lamprotula and Aculamprotula). In our 2007 checklist, we classified Inversiunio among the Unioninae and Inversidens under the Gonideinae.

Way back in 1970, Starobogatov had coined the name Pronodularia for Inversidens japanensis, but no one really took notice. The Soviets had a knack for making up unnecessary new names for mussels. However, Kondo (2008) applied the genus name to distinguish P. japanensis from its former congeners. Why? Good question.

We anticipate that further phylogenetic scrutiny of the Old World mussel genera will uncover and resolve heretofore unknown mussel confusions.

* Actually, we don’t really know any unambiguous morphological synapomorphies that put Inversidens, Pronodularia, and the other genera of the Gonideinae in that subfamily, but the molecules seem to support such a clade (Pfeiffer & Graf, 2015).


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONIDAE Rafinesque, 1820
Subfamily GONIDEINAE Ortmann, 1916

Genus Pronodularia Starobogatov, 1970

Species Pronodularia japanensis (Lea, 1859)

To find out what you can about Pronodularia and other eastern Palearctic freshwater mussels, check out:
  • 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.
  • Kondo, T. 2008. Monograph of Unionoida in Japan (Mollusca: Bivalvia). Special Publication of the Malacological Society of Japan (3): 69 pp.
  • Pfeiffer, J.M. & D.L. Graf. 2015. Evolution of bilaterally asymmetrical larvae in freshwater mussels (Bivalvia: Unionoida: Unionidae). Zoological Journal of the Linnean Society.
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