Page last updated
11 November 2014
Unionoida cum Grano Salis
The Nearctic Region includes all of North America, north of the Mexican Plateau. It is the most most species-rich region in the world, with 302 species. The families represented are Unionidae and Margaritiferidae.
Nearctica is composed of five subregions. The largest is the Interior Subregion (NA1; 134 spp.) which includes the Mississippi Basin and the adjacent, formerly glaciated of the Great Lakes and the Canadian Interior Basin. The streams draining directly to the Atlantic comprise the Atlantic Subregion (NA2; 57 spp.), which extends from the glaciated portions of eastern Canada and the USA, south to Georgia. The Gulf Subregion (NA3; 142 spp.) is a real hot-spot of freshwater mussel diversity that occurs from the Rio Grande Basin in Mexico, east to the Suwanee in Florida. Sandwiched in between the Atlantic and Gulf subregions is the Florida Subregion (NA4; 13 spp.) which occupies peninsular Florida. West of the continental divide is the Pacific Subregion (NA5; 9 spp.). It is unclear whether the assemblage of the Pacific Subregion shares closer affinities with the rest of Nearctica or eastern Palearctica.