[Generic divisions of Cooperiinae nematodes (Trichostrongylidae)]

Presence of a functional synlophe seems to be connected to presence of a cephalic vesicle in the Trichostrongyloidea and the Cooperiinae, the only members of the Trichostrongylidae with a cephalic vesicle, are also the only members with a functional synlophe. Hypotheses concerning the evolution of the Cooperiinae are suggested on the basis of modifications of the synlophe consisting fundamentally of 5 dorsal and 5 ventral crests, and 3 pairs of small lateral crests oriented perpendicular to the body. Arising from Chabaudstrongylus (parasites of Tragulidae and Cervidae), Cooperia has evolved in three directions: a) increase in the number of pairs of lateral crests; b) hypertrophy of ventral crests; c) appearance of a dorso-ventral axis of orientation of crests. Impalaia, Ortleppstrongylus (the only genus in the group parasitizing rodents and not ruminants) and Minutostrongylus retained the primitive synlophe and evolved in the direction of monodelphy. Megacooperia is characterized by hypertrophy of lateral crests and Paracooperia by this as well as the appearance of a dorso-ventral axis of orientation to the synlophe. Cooperioides is placed in synonymy with Cooperia; Minutostrongylus is recognized as valid.