Allocrangonyx is a genus of troglobitic amphipod crustaceans from the South Central United States.[3] The two species are both listed as vulnerable on the IUCN Red List.[4][5] The animals are blind and unpigmented. During the male's development, the outer ramus of the third uropod differentiates into secondary segments and grows to a length greater than the animal's body length.[6]
| Allocrangonyx | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Amphipoda |
| Family: | Allocrangonyctidae Holsinger, 1989 [2] |
| Genus: | Allocrangonyx Schellenberg, 1936 [1] |
| Species | |
| |
Allocrangonyx pellucidus
A. pellucidus, the "Oklahoma cave amphipod",[1] is known from caves and springs in the Arbuckle Mountains of Johnston, Murray and Pontotoc counties, Oklahoma.[7] The largest males reach 21.75 mm (0.856 in) long, while females reach 18 mm (0.71 in).[3]
Allocrangonyx hubrichti
A. hubrichti, the "Central Missouri cave amphipod"[1] or "Hubricht's long-tailed amphipod",[6] was thought for many years to be endemic to the state of Missouri, but specimens were discovered in 1996, 283 km (176 mi) away, in a water well near Romance, White County, Arkansas.[8] While the well is drilled into Pennsylvanian age sandstone, all previous records have been from Ordovician limestones and dolomites.[8]