ABATHYMERMIS-FISERI N-SP AND ABATHYMERMIS-SHOCKI N-SP (NEMATODA, MERMITHIDAE) FROM MIDGE (DIPTERA, CHIRONOMIDAE) IMAGOS EMERGING FROM LAKE ITASCA, MINNESOTA, USA

Abathymermis fiseri n. sp. and Abathymermis shocki n. sp., two closely related species of mermithid nematodes, are described from adult chir onomids emerging from Lake Itasca, Minnesota in early June of 1992 and 1993. These are the first two species of Abathymermis reported outsid e the Palearctic Realm. The species are distinguished from other suffi ciently described members of the genus by their larger size, long prot ractor and abbreviated bursal musculature, longer spicules, and the po sition of the posterior extention of the trophosome in the male. A. fi seri n. sp. and A. shocki n. sp. are separated by several quantitative characteristics including spicule lengths, body widths at most levels , and number of genital papillae. In addition the pointed tail and the presence of cephalic superficial cuticular annuli in A. shocki n. sp. differ from the rounded tail and absence of annuli in A. fiseri. n. s p. Eggs of A. fiseri n. sp. require fertilization to initiate embryoge nesis, while eggs of A. shocki n. sp. can develop parthenogenetically, although males are known-the first demonstration of parthenogenesis r esulting in viable offspring in an aquatic mermithid. The host chirono mid species remain unknown. Eleven species of mermithids from eight ge nera have now been reported from Lake Itasca chironomids. Lake Itasca chironomids.