A notable peculiarity of some species in this family is a tendency to extensions of the body wall in the vicinity of or including the male pores.

These extensions may be mere protuberances, as in some species of Drilocrius; or involve a greater extent of the body wall, as in genus Glyphidrilocrius.

They take the form of wing or keel-like structures called alae in Glyphidrilus species and paddle-shaped claspers in Drilocrius alfari.

A possibly related family, Criodrilidae, contains genera Criodrilus and Biwadrilus with male pores in 15 and 13, respectively.

Spermathecae are absent (a rare condition in oligochaetes) and one to several spermatophores containing the sperm are transferred between partners and attached near the genital field.