The nymph and reared male and female of a new ephemerellid species, which was collected from southern China and named Teloganopsis setosa Zhou, sp. n., are described. The nymph is unique because of its long and dense setae on labrum, mandibles, maxillae, labium, and forelegs as well as the elongated segments II of labial palpi and expanded paraglossae. The male can be differentiated from close relatives by its larger penis lobes with dorsolateral projections, and the more pigmented tergum IV and caudal filaments. The nymph described in this paper represents a new adaptive and ecological type in the family Ephemerellidae.
Keywords: Mayfly; evolution; filter; new species; taxonomy.