Mussel of the

Page last updated
4 July 2024

Mussel of the Month

The July 2024 Mussel of the Month is Postolata guangxiensis. Postolata is a genus of two species endemic to southern China.

Postolata guangxiensis
22_NCU_XPWU_PGF01. Guangxi, Guilin City, Yongfu County, Luoqing River.

Postolata guangxiensis is a recently discovered freshwater mussel species in a recently described genus. The shell pic above was graciously provided by Yu-Ting Dai and Prof. Xiaoping Wu. This month is a special one to honor a newly added species because this is the month where our tally of Recent freshwater mussel species broke through the 1000-species-ceiling. As of this posting, the MUSSEL Project Database records 1004 valid species of freshwater mussels!

Now, you might be saying, Wait?! That is what everybody has been saying for a long time. Lots of web pages about freshwater mussels say there are “over 1000 species” worldwide — google it. It is textbook: “nearly 1200 species” (Boss, 1982, p. 1123), “about 1,200 species” (Brusca & Brusca, 1990, p. 708).

That number dates from Simpson (1914). He listed more than 1300 species. About mid-century, Haas (1969) reported 837 species, but lots of people didn’t have access to that work, and Simpson’s tally stuck for the 20th century.

When we did our first global checklist, we found 840 freshwater mussel species being used as valid in the literature (Graf & Cummings, 2007). As more data became available, that number grew. We reported those updates on this website and in a few publications when we had the opportunity (e.g., Graf, 2013: 859 spp., Graf & Cummings, 2019: 918). By the time we submitted our second global checklist for publication in 2019, the MUSSELpdb had 915 species. That grew to 958 during the time that manuscript was in review (Graf & Cummings, 2021)! The article discussed in detail the nature of the changes between 2007 and 2021.

Since then, we have been continually updating the MUSSELpdb and serving the data. Starting in October 2021, each Mussel of the Month post has come with a graph of known species richness over time, just like the one at the bottom of this page. The geography summary page provides a current geographical accounting of species (and genus) richness. This month is the first in MUSSELp history to top 1000 valid species!

graph of species richnessThe graph to the right depicts the changes in species richness in each geographical region since 2021. East Asia has added the most species in that time: 25 (including Postolata guangxiensis), to bring the regional total to 345 species. It has long been stated that North America has the richest mussel fauna in the world (307 spp.), but that is no longer true (although the southeastern United States is a global hotspot that remains hotter than other hotspots).

It has also long been taken as fact that Europe has a depauperate mussel fauna. It certainly does relative to East Asia and North America. But, freshwater mussel species richness in North Eurasia grew by more than a third since 2021, the fastest rate in world!

We will keep keeping an eye on richness and classification, and we will continue updating this web site as we all keep refining our appreciation of global freshwater mussel diversity.


Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Superfamily UNIONOIDEA Rafinesque, 1820
Family UNIONIDAE s.s.
Subfamily GONIDEINAE Ortmann, 1916
Tribe GONIDEINI s.s.

Genus Postolata Dai, Huang & Wu in Dai et al., 2023

Species Postolata guangxiensis Dai, Huang, Guo & Wu in Dai et al., 2023

To find out more about Postolata and the global species richness of freshwater mussels, check out:
  • Boss, K.J. 1982. Mollusca. pp. 945-1166 in Synopsis & Classification of Living Organisms, Vol. 1 (S.P. Parker, ed.). McGraw-Hill Book Company, New York., NY.
  • Brusca, G.J. & R.C. Brusca. 1990. Invertebrates. Sinauer Associates, Inc., Sunderland, MA.
  • Graf, D.L. 2013. Patterns of freshwater bivalve global diversity and the state of phylogenetic studies on the Unionoida, Sphaeriidae, and Cyrenidae. American Malacological Bulletin 31: 135-153.
  • 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.
  • Graf, D.L. & K.S. Cummings. 2019. Unionidae Rafinesque, 1820 and the general Unionida. pp. 202-209 in Freshwater Mollusks of the World: A Distribution Atlas (C. Lydeard & K.S. Cummings, eds.). Johns Hopkins University Press, Baltimore, MD.
  • Graf, D.L. & K.S. Cummings. 2021. A 'big data' approach to global freshwater mussel diversity (Bivalvia: Unionoida), with an updated checklist of genera and species. Journal of Molluscan Studies 87(1): eyaa034.
  • Haas, F. 1969. Superfamilia Unionacea. Das Tierreich (Berlin) 88: 663 pp.
  • Simpson, C.T. 1914. A descriptive catalogue of the naiades, or pearly fresh-wa Parts I-III. Published by Bryant Walker, Detroit, Michigan. 1540 pp.

current tally

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