Unionoida cum Grano Salis

Page last updated
8 August 2018

Unionoida cum Grano Salis

Geographical Summary

We currently list 927 species of freshwater mussels worldwide. This diversity, however, is not randomly distributed. Based upon the geographical distributions of the numerous genera and species, we have divided the mussel-inhabited continents of the Earth into six regions, each with multiple subregions. Each region is depicted with a different color in the map below. Areas in gray are without mussels.

Freshwater Mussel Regions of the World

  • Nearctica. — The Nearctic Region includes all of North America, south to the Mexican Plateau. It is divided into five subregions. Total richness: 62 genera, 310 species.
  • Neotropica. — The Neotropical Region includes all of South America, north to the Mexican Plateau. The region is divided into six subregions, 5 in South America and 1 for Central America. Total richness: 41 genera, 217 species.
  • Afrotropica. — Sub-Saharan Africa, the Nile Basin and Madagascar are grouped as the Afrotropical region. The region is partitioned into six subregions. Total richness: 16 genera, 79 species.
  • Palearctica. — The Palearctic Region consists of northern Eurasia from the Atlantic to the Pacific, including northern Africa and the Middle East. It is subdivided into five subregions. Total richness: 22 genera, 65 species.
  • Indotropica. — Southern and southern Asia (including the Philippines and much of Indonesia) are treated as the Indotroical Region. It is divided among four subregions. Total richness: 55 genera, 246 species.
  • Australasia. — The Australasian Region is composed of Australia, New Zealand and New Guinea (as well as some smaller islands). The area is subdivided into four subregions. Total richness: 10 genera, 30 species.

As has been frequently recognized, Nearctica has the richest mussel assemblage in the world. It is less frequently stated, however, precisely how much more diverse it is than other areas. The nearest contenders, with regard to species richness, are Neotropica and Indotropica. The southern continents are relatively less diverse (especially when their land area is considered). This is presumably due to both the relative habitat instability of those regions and the fact that those areas are less well studied.

These regions all have endemic lineages, and more information about taxonomy can be found under our Taxonomic Summary.


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