Morphological Study of Qaidamestheria (Spinicaudata) from the Middle Jurassic in Qinghai, Northwestern China

Abstract

Abstract. The Triglypta–Qaidamestheria clam shrimp assemblage, widely known from the non-marine Jurassic deposits in northern China, is important for biostratigraphic correlation of the fossil bearing strata. Qaidamestheria Wang, 1983, an essential component of the assemblage, was originally described from the upmost oil shale member of the Dameigou Formation at the northern margin of the Qaidam Basin, northwest China. Though the original description of the genus Qaidamestheria was based on SEM microscopy, the published pictures of the type specimens are unclear, and the type specimens were lost. We collected new specimens of the type species Qaidamestheria dameigouensis Wang, 1983 from the 7th unit of the Dameigou Formation in the Dameigou section, where the holotype of the species was originally collected. The examination of the specimens under SEM has revealed three critical taxonomic features for the genus: the fine reticulation (mesh diameter 7–18 µm) on the larval valve and several adjacent growth bands; the transitional (reticulated-punctate) ornamentation on the middle–ventral part of the carapace; and linearly arranged puncta appearing only on growth bands near the antero-ventral margin of the carapace, puncta never clustered.