Gastromermis massei n. sp. (Nematoda: Mermithidae) a parasite of blackflies Simulium wolffhuengeli Enderlein (Simuliidae: Diptera) in Argentina

Gastromermis massei n. sp. (Nematoda: Mermithidae) is described and illustrated. This species was found parasitizing Simulium wolffhuengeli Enderlein (Simuliidae: Diptera) in the Cosquin River in Cordoba, Argentina. It can be distinguished from the other species of the genus by the following characters: number (six) of hypodermal chords, position of the mouth, shape of amphidial pore, absence of vulval flaps, length of spicule, shape of proximal and distal ends of spicule, number of genital papillae, and length of tail appendage of postparasitic juveniles. G. massei n. sp. is the sixth species of Gastromermis described in Argentina; among Mermithidae, this genus is the most common in the country. A key to the species of Gastromermis with six hypodermal chords is proposed.