A new mermithid species (Nematoda) from chironomid imagos eclosing from Lake Ozawindib in northern Minnesota.

Hydromermis biesboeri n. sp. (Nematoda: Mermithidae) is described from the hemocoel of imagos of chironomid host species eclosing from Lake Ozawindib in northern Minnesota in July and August 2008 and 2009. The new species is distinguished from the other 28 described species in the genus by terminal mouth, wide oval (male) and long oval (female) amphids with a dorsal commissure, tapered and rounded posterior ends, split base of the spicule, short protractor muscles in males, and by females having an S-shaped vagina with equal-length terminal limbs. The new species represents the 10th Hydromermis mermithid species described, or reported, from the region and the second from Lake Ozawindib.