The genetic structure and evolutionary history of an endemic anchialine species, the shrimp Halocaridina rubra Holthuis, 1963 (Crustacean: Decapoda: Atyidae), was investigated across its range in the Hawaiian archipelago using mitochondrial (e.g., cytochrome oxidase subunit I and large subunit ribosomal) gene sequences. A survey of 573 individuals collected from 34 sites on the islands of Hawai’i, Maui, and Oahu revealed 13 di...