The October 2025 Mussel of the Month is Anodontites lurulenta
The recent revision of Central American freshwater mussels is a major biodiversity “correction"
Even if you are the kind of person with freshwater mussels frequently front-of-mind, you might not recognize the significance of Anodontites lurulenta as a new genus-species combination. The Mussel of the Month is known only from the original type series of three pairs of valves from the Usumacinta River of the Mexican Yucatan. Until last month, almost everyone (which, as explained below, is very few) had classified this mussel as Anodonta lurulenta in the family Unionidae. Reclassification to Anodontites shifts the species to the family Mycetopodidae. Such seismic shuffling from one family to another is rare nowadays. There have only been two others so far this century: Gibbosula from Unionidae to Margaritiferidae and Moncetia from Iridinidae to Unionidae (Graf & Cummings, 2021). When soft-parts (i.e., the non-shell anatomy like the mantle, gills, foot, larvae, and reproductive structures) are known, correct classification to family is trivial. When all we have are shells, that kind of extrapolation is more challenging.
The reclassification of Anodontites lurulenta was just one of the revisions we made in our new book, Freshwater Mussels of Central America, published in September by Routledge (Cummings et al., 2025). Though a few species and genera were resurrected from the purgatory of synonymy, many more were sunk into invalidity for a net loss of almost 30 species! The hotspot of Central American freshwater mussel diversity got a little bit cooler.
When we synthesized our first global checklist and regional diversity assessment of freshwater mussel species and genera, we estimated 102 species in Central America (Graf & Cummings, 2007: Table 5). Central America extends from Mexico south of the Rio Grande Basin to Panama. (The Rio Grande is assigned to the Gulf of Mexico-Florida subregion of North America in our system.) Back then, that tally placed the species richness of Central America as third in the whole world (after the Interior Basin and Gulf Coastal Basins of North America), exceeding the richness of South America! At the time, we largely followed Haas (1969), the last work to summarize the species of the region. That’s a gap of almost 40 years between updates, and our primary changes involved elevating subgenera to genera, rather than novel circumscriptions of species. There simply had not been significant updates since Haas.
However, the taxonomic stability/stagnation goes back even further. Haas’s (1969) accounting was little different from the checklist published by Frierson (1927), with a few of his own contemporaneous revisions (e.g., Haas, 1930). That is back in time another 50 years! The species we listed for Central America in Graf & Cummings (2007) were by necessity based on revisionary work pre-dating the Neo-Darwinian Synthesis and the Biological Species Concept, let alone the Phylogenetic Revolution. At the time we expected a modern appraisal might result in some major modifications to that too-high estimate of 102 species.
The Excel spreadsheet linked below compares the genus- and species-level classifications of Frierson (1927) and Haas (1969), as well as Graf & Cummings (2021) and Cummings et al. (2025).
Going back further in time, the other major works to tackle Central American freshwater mussels were Simpson (1900, 1914), Martens (1900), and Fischer & Crosse (1894). Perhaps in some future post, we can take up those more antiquated and outdated taxonomies, but we haven’t the time, space, or need to worry about those now.
Graf & Cummings (2021: Table 4) updated the global review of Graf & Cummings (2007), and the number of freshwater mussel species in Central America was reduced to 94. Much of the meager difference was due to the lumping of species in the genera Delphinonaias (Goodrich & van der Schalie, 1937) and Psoronaias (+ Psorula) (Pfeiffer et al., 2019). However, as far as species richness, Central America still ranked 4th, after the Interior Basin and Gulf of Mexico Basins of North America, and Indochina. For the most part, our estimate of species richness in Central America in 2021 was practically the same as it had been. The little drop in Central American species richness contrasted with the large increases seen in South America, Europe, and East Asia mussels-over the same period.
With the publication of Cummings et al. (2025), we have the first comprehensive revision of Central American freshwater mussels since Frierson (1927). The research was based on several field expeditions to the region led by Kevin Cummings as well as museum work and reexamination of type specimens. Consequently, Freshwater Mussels of Central Americaprovides color illustrated documentation of natural environments, exemplar specimens (especially types), and maps of species ranges, with comprehensive synonymies and an extensive bibliography. Ninety-eight years was well worth the wait!
The taxonomic and specimen data from Cummings et al. (2025) have been integrated into the MUSSEL Project Database, and the updated version of “Table 4” from Graf & Cummings (2021) (showing species richness and endemism by region and subregion) is available on our web site. From 102 species down to 94 species, and now down to 66! That decrease in freshwater mussel species richness now makes Central America the 6th richest subregion in the world and third in the Americas. Still a hotspot, just not quite as hot.
While no new names were introduced by Cummings et al. (2025), the ledger of freshwater mussel species in Central America gained seven — all of them elevated from the synonymy of other species. But, 35 species were crossed off, for a net loss of 28 (=94-66). Two of those removals resulted from splitting. When Pyganodon globosa was resurrected to represent the disjunct Mexican populations formerly known as P. grandis, the latter species became restricted to North America. A similar situation obtained for Mycetopoda subsinuata, split from M. siliquosa and now limited to South America. Twenty-six species were lost by lumping them into other species, and the remaining seven were just dropped as the dirty little nomina dubia that they are (i.e., type specimens that can’t, for whatever reason, be assigned to a valid species).
We also put some older genus names back to work, elevating Mesonaias and Brachyanodon for Central American species of Cyrtonaias and Anodonta, respectively. Three genera were synonymized away: Martensnaias (=Psoronaias), Barynaias (=Psoronaias), and Reticulatus (=Arotonaias). This doesn’t even consider all the species like our Mussel of the Month that have been reclassified from one genus to another!
That downward “correction” of 28 species in Central America plunges the total global richness of freshwater mussels below 1000 species for the first time since July 2024!
Whereas malacologists in other parts of the world have been bullishly increasing the known diversity of freshwater mussel species and genera, Central America is still waiting for the same comprehensive molecular phylogenetic research. Until then, Freshwater Mussels of Central America by Cummings et al. (2025) is a giant leap forward and a major achievement by a good friend of mine.
References Cited
Cummings, K.S., D.L. Graf, J.M. Pfeiffer, & J.S. Tiemann. 2025. Freshwater Mussels of Central America. CRC Press, Boca Raton. 496 pp.
Fischer, P., & H. Crosse. 1894. Études sur les mollusques terrestres et fluviatiles du Mexique et du Guatemala. Mission Scientifique au Mexique et dans l’Amérique Centrale. Recherches Zoologiques pour servir á l’Histoire de la Faune de l’Amérique Centrale et du Mexique. Septiéme Partie. 15th Livraison. Feuilles 62–82, pp. 489–656, plates 59–66, Imprimerie Nationale, Paris V ol. 2. 731 pp.
Frierson, L.S. 1927. A Classification and Annotated Check List of the North American Naiades. Baylor University Press, Waco, Texas. 111 pp.
Goodrich, C., & H. van der Schalie. 1937. Mollusca of Petén and North Alta Vera Paz, Guatemala. Miscellaneous Publications, Museum of Zoology, University of Michigan, Ann Arbor, Michigan. No. 34. 50 pp.
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. 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 (36 pp.).
Haas, F. 1930. Über nord–und mittelamerikanische Najaden. Senckenbergiana 12(6): 317–330.
Haas, F. 1969. Superfamilia Unionacea. Das Tierreich, Leif. 88. Walter de Gruyter and Co., Berlin. 663 pp.
Martens, E.v. 1890–1901. Land and freshwater Mollusca. In F.D. Godman, and O. Salvin (eds.). Biologia Centrali‑Americana, Vol. 9. R. H. Porter, London. 706 pp., 44 plates. https://www.biodiversity‑library.org/bibliography/730
Pfeiffer, J.M., C.L. Atkinson, A.E. Sharpe, K.A. Capps, K.F. Emery, and L.M. Page. 2019. Phylogeny of Mesoamerican freshwater mussels and a revised tribe‐level classification of the Ambleminae. Zoologica Scripta 48(1):106–117.
Simpson, C.T. 1900. Synopsis of the naiades, or pearly fresh-water mussels. Proceedings of the United States National Museum 22: 501-1044.
Simpson, C.T. 1914. A Descriptive Catalogue of the Naiades, or Pearly Fresh-water Mussels. Parts I-III. Bryant Walker, Detroit, Michigan. 1540 pp.