Mussel of the

Page last updated
2 September 2020

Mussel of the Month

The September 2020 Mussel of the Month is Diplodon paranensis. Diplodon is a genus of 43 species from South America.

Diplodon paranensis
CM_61.9265. Rio de la Plata, San Isidro, 20 km N Buenos Aires, Argentina.

Diplodon, as currently classified, is the sole Recent genus of the Tribe Rhipididontini.* It is by far the most species-rich freshwater mussel genus, with 43 species.*** We have covered Diplodon as Mussel of the Month twice before: D. chilensis and D. parallelopipedon.

The classification of Diplodon is a mess, and different authorities have toyed with splitting the species among two subgenera or genera: Diplodon and Rhipidodonta. Simone (2006) split them at the full-on genus level, whereas Pereira et al. (2014) opted for subgenera. Back in 2007, we followed the former (Graf & Cummings, 2007), and now the MUSSELpdb lines up with the latter (i.e., everything is classified under Diplodon). Back in the day, Parodiz (1968) and Haas (1969) published revisions but without much consensus. There is no phylogeny of Diplodon. In fact, no one has included more than three Diplodon species at the same time in a phylogenetic analysis (Santos-Neto et al., 2016).****

Diplodon paranensis is the type species of Rhipidodonta. So, while today, it represents a tripling-up on Diplodon as Mussel of the Month, someday, when the winds of taxonomy change, this MotM might be reclassified.

* You might think Diplodontini Ihering, 1901 would be the valid name for the tribe, as Parodiz & Bonetto (1963) did, but that name is preoccupied by Diplodontidae Carpenter, 1861 (= Ungulinidae Gray, 1854). Although Diplodon and Diplodonta are different genera, their Latin root conjugates** into the same family-group name.

** I don’t care if that isn’t the correct verb.

*** The top 5 most species-rich genera are rounded out by Elliptio (30 spp.), Epioblasma (28), Lampsilis (26), and Anodontites (26). Pleurobema, Coelatura, and Nephronaias also have more than 20 species each.

**** And their results made no sense.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820
Family HYRIIDAE Swainson, 1840
Subfamily HYRIINAE s.s.
Tribe RHIPIDODONTINI Starobogatov, 1970

Genus Diplodon Spix in Wagner, 1827

Species Diplodon paranensis (Lea, 1834)

To find out more about Diplodon and the classification of South American freshwater mussels, check out:
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