The snuffbox is now found in just 79 streams, a 62 percent decline in its range. Of those 79 streams, 29 are known to have only one or two living individuals.
The rayed bean has suffered an even more dramatic 73 percent decline in the number of streams and lakes that once were home to the species. It is now known in just 31 streams and one lake.
Both species have been devastated by dams that either cut off entire reaches of their habitat or created slackwater conditions that prevent the mussels from moving about to reproduce.
Chemical spills and water removal for fracking to extract natural gas from shale deposits are also threats to the two species, according to the USFWS action.
The listing becomes effective March 15.
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