Contribution to the biology and systematics of Ephemerella alleni (Ephemeroptera: Ephemerellidae)

The adult stages of the western Nearctic species Ephemerella alleni Jensen & Edmunds are described for the first time based on reared specimens from Mount Rainier National Park, Washington, USA. Male adults are distinguished by having ganglionic marks on the abdominal sterna, genital forceps segment 2 with a distal expansion, penes with short apical projections, and spinulelike setae medially near the outer margin and along the inner margin of the medioapical cleft. Eggs have a smooth chorion. Larvae are distinguished from congeners by having a smooth frons and abdominal terga with distinctive paired spines. Morphological variability in these and other structures can confound identification of single specimens or short series of specimens. Our collection data represent the first new records of the species since its original description in 1966.