Schimperella acanthocercus, a new species of lophogastrid crustacean, is described from the Triassic of southwest China. This species is very similar to modern forms as well as the rare fossil Lophogastrida, known to date only from the Jurassic and Triassic. The sister “mysidacean” group to the Lophogastrida, the Mysida, are also rare in the fossil record; they too demonstrate remarkable similarities to living forms, suggesting that the extant “mysidaceans” had achieved “stable body plans” relatively early in their history, certainly by the Jurassic and Triassic. The third “mysidacean” group, the Pygocephalomorpha, have a considerably more extensive fossil record and are thus better understood. While “mysidaceans” are relatively rare in the fossil record, enough is known to suggest some possible biogeographic and evolutionary relationships.