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Gammarus desperatus is a medium sized species of gammarid amphipod that is endemic to the southwestern United States. It was described in 1981 by Gerald A. Cole from a locality known as North Spring in Roswell, New Mexico (Cole, 1981). North Spring is located on property owned by the Roswell Country Club and has been heavily modified. As a result, Gammarus desperatus has been extirpated from its type locality (Lang, 1999; 2002). It currently survives at the Bitter Lake Wildlife Refuge in Chaves County, New Mexico where it is known from several localities (Lang, 1999; 2002). Due to its limited range, Gammarus desperatus is at risk for extinction and has been listed as Critically Endangered on the IUCN Red List, and as an endangered species under the US Endangered Species Act (Lang et al., 2000; ECOS, 2016). The epithet desperatus was given by Cole to describe the ‘hopeless’ situation that Gammarus desperatus was in, being restricted to what was then thought to be a single spring in an unstable area where springs were drying at “alarming rates” (Cole, 1981). Like most amphipod species, at first glance Gammarus desperatus is morphologically indistinct. However, close examination reveals several features that differentiate it from other Gammarus spp. The type locality of Gammarus desperatus has been described as moderately saline, which is similar to other springs with amphipods in the region (Cole, 1981). Analyses of the salinity of springs in the northern Chihuahuan desert, have found ambient salinities ranging from 0.5-9 parts per thousand, with ‘spikes’ reaching 21 ppt. Indicating a high salinity tolerance for Gammarus desperatus and other amphipods in the region (Seidel et al., 2010). Like other freshwater amphipods Gammarus desperatus is a detritivore, feeding on decomposing plant and animal matter. Amphipods of the genus Gammarus are also noted for occasionally displaying cannibalistic and predatory behavior (Thorp et al, 2014).