A complete description of the xinjiangchelyid turtles Annemys levensis and A. latiens is provided, based on all available material from the Upper Jurassic type locality of Shar Teg, Mongolia. Annemys latiens was previously known almost exclusively from shell material, but an undescribed skull from Shar Teg is referable to this species and its distinct morphology confirms the presence of two taxa at this locality. Annemys latiens has an elongated skull that markedly differs in proportions from those of A. levensis and resembles the shape of some recent, piscivorous turtles. The overall similarity of the shells of the two Annemys species combined with significant differences in the skull indicate that these turtles probably partitioned the aquatic niche by exploring different feeding strategies. Among xinjiangchelyids, at least three different skull morphotypes can be differentiated, which implies a moderate level of ecological diversification among Late Jurassic Asian turtles. Phylogenetic analysis weakly supports the inclusion of Annemys spp. into Xinjiangchelyidae and places xinjiangchelyids at the stem of Testudines, but the latter result is considered tentative. Phylogenetic definitions of Xinjiangchelyidae, Sinemydidae, and Macrobaenidae are provided for nomenclatural clarity and precision.