''Allocrangonyx'' is a genus of troglobitic

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s from the

South Central United States The South Central United States or South Central states is a region in the south central portion of the Southern United States. It evolved out of the Old Southwest, which originally was the western portion of the South. The states of Arkansas, ...

. The two species are both listed as vulnerable on the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

. The animals are blind and unpigmented. During the male's development, the outer ramus of the third

uropod Uropods are posterior appendages found on a wide variety of crustaceans. They typically have functions in locomotion. Definition Uropods are often defined as the appendages of the last body segment of a crustacean. An alternative definition sugge ...

differentiates into secondary segments and grows to a length greater than the animal's body length. Turner falls ok

''Allocrangonyx pellucidus''

''A. pellucidus'', the "Oklahoma cave amphipod", is known from caves and springs in the

Arbuckle Mountains The Arbuckle Mountains are an ancient mountain range in south-central Oklahoma in the United States. They lie in Murray, Carter, Pontotoc, and Johnston counties.

of Johnston,

Murray Murray may refer to: Businesses * Murray (bicycle company), an American manufacturer of low-cost bicycles * Murrays, an Australian bus company * Murray International Trust, a Scottish investment trust * D. & W. Murray Limited, an Australian who ...

and Pontotoc counties,

Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...

. The largest males reach long, while females reach .

''Allocrangonyx hubrichti''

''A. hubrichti'', the "Central Missouri cave amphipod" or "Hubricht's long-tailed amphipod", was thought for many years to be

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to the state of

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

, but specimens were discovered in 1996, away, in a

water well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...

near Romance, White County,

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the Osage ...

. While the well is drilled into

Pennsylvanian Pennsylvanian may refer to: * A person or thing from Pennsylvania * Pennsylvanian (geology) The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the International Commission on Stratigraphy, ICS geologic timesca ...

age

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

, all previous records have been from Ordovician

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

References

{{Taxonbar, from=Q3933396 Gammaridea Crustaceans of the United States Freshwater crustaceans of North America Taxonomy articles created by Polbot