Quantitative morphological comparison of rake-legged mites over the last 100 million years and the first fossil larva of Caeculidae

Abstract Rake-legged mites (Caeculidae) are ambush predators. The fossil record of the group Caeculidae is scarce, but includes a few well-preserved specimens in Miocene, Eocene and Cretaceous ambers. We report newly discovered specimens from approximately 100-million-year-old Kachin amber in Myanmar. The specimens possess the typical raptorial forelegs bearing spine-like setae with extended sockets. One of the new specimens, and possibly also another one, represents a six-legged larva, the first larva of Caeculidae known for Kachin amber, and seemingly for the entire fossil record of the group. A quantitative morphological analysis reveals that most fossils share similar morphologies with modern species. Extant specimens occupied a larger morphospace, indicating a possible recent diversification of the lineage. However, it could be explained by a sampling bias since fossils of Caeculidae are still rare. Only one of the new fossil specimens differs from the modern forms in morphology, which points to a possible different ecology.