ORDER: Ephemeroptera
FAMILY: Ephemerellidae

The mayfly Ephemerellidae is distinguished by the absence of gills on the second abdominal segment; individuals either have gills on segments 3-7 or 4-7. Some may have operculate (plate-like) gills on the fourth segment, though in many the gills are of identical size.

Commonly encountered genera include Drunella, Ephemerella, and Serratella.