Stygotantulus stocki is a species of crustacean, living as an ectoparasite on harpacticoid copepods of the families Tisbidae and Canuellidae. It is the smallest arthropod in the world, at a length of less than 0.1 millimetres (0.004 in). The specific epithet stocki commemorates Jan Hendrik Stock, a Dutch carcinologist.