Faxonius peruncus, the Big Creek crayfish, is a species of crayfish in the family Cambaridae. It is endemic to Missouri. The common name refers to Big Creek, where the original specimens were found.[1]
F. peruncus is limited to the St. Francis River watershed.
The main threat to this species is a related species, F. hylas which was introduced into the area in 1984. F. hylas out-competes, and hybridises with, F. peruncus. Also, pollution from the Southeast Missouri Lead District affects the water quality in the local area.