''Cyprinodon arcuatus'' (Santa Cruz pupfish) is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of fish in the family Cyprinodontidae. It was

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 Santa Cruz River in

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

. It has been declared

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

as of 2011.

Description

The Santa Cruz pupfish exhibited

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

in size, with males averaging 37mm (1.46in) in length and females averaging 32mm (1.26in) in length. Coloration in breeding males was dark green to black with alternating stripes of light and dark. Female and non-breeding males were reported to have clear fins except for a black dorsal fin. ''C. arcuatus'' is differentiated from other '' Cyprinodon '' species by a highly convex dorsal body and concave post-dorsal body, as well a lack of orange or yellow in breeding males' fins.

References

{{Taxonbar, from=Q3760866 arcuatus Taxa named by Wendell L. Minckley Taxa named by Robert Rush Miller Fish described in 2002 Endemic fauna of Arizona Fish of the Western United States Freshwater fish of the United States Fish of North America becoming extinct since 1500