Agrenia polymorpha Fjellberg, 1986

This species occurs in the Canadian and U.S. Rocky Mountains where it lives in wet moss along streams, springs and waterfalls. Fjellberg (1986) described a complex sexual polymorphism and allometric growth pattern affecting the shape and relative length of the antennae, and changes in setae and structure of the cuticle. Diagnostic characters of the species are presence of a mucronal seta in combination with few anterior setae on the ventral tube (fewer than 13), uniform body colour, and sexual polymorphism.