TROPHOMERMIS-ITASCENSIS N-GEN, N-SP (NEMATODA, MERMITHIDAE), AN IMAGICIDAL PARASITE OF CHIRONOMIDS IN LAKE ITASCA, MINNESOTA, USA

Trophomermis itascensis n. gen., n. sp. is described from chironomid i magos of Tanytarsus neoflavellus and Ablabesmyia (Karelia) illinoensis emerging from Lake Itasca, Minnesota, U.S.A. The genus is distinguish ed on the basis of being tetrapapillate, unispiculate, and hexacordal, and in having an acute posterior terminus and a straight diagonally d irected vagina. Additionally, the new genus lacks a cross-fiber layer in the cuticle and has a terminal mouth and a long buccal funnel. The amphidal openings are posterior to the small cephalic papillae. No lar val horn is present. The trophosome is unusual in that it abuts agains t the nerve ring and sometimes extends anterior to the nerve ring. In the male, the trophosome extends posteriorly beyond the genital pore a s a separated unit. Information also is provided on bionomics and vari ants observed.