Pecatonica River Mayfly (Acanthametropus pecatonica), a State Endangered species, is known only from nymphal specimens. The mature nymph is about 20mm long, creamy white with three short tail filaments densely fringed on the margins, a small head with lateral eyes, and abdominal segments one through seven each bearing a distinctive pair of plumelike gills. Paired spines of the head, thorax, and a row of dorsal abdominal spines distinguish this nymph. There is no information known about the adult mayfly and repeated attempts to rear Wisconsin nymphs to adulthood have been unsuccessful. The species habitat requirements include sand-bottom rivers with little water pollution. The specimens found in Wisconsin have been collected from large, sand-bottomed rivers with wide channels, in water a meter or less deep. Records from Illinois are from moderately sized, fast, shallow streams with sand and rock bottoms.
