Morphological variation in three mermithids (Nematoda) from Chironomidae (Diptera) and a reassessment of the genera Gastromermis and Hydromermis

Abstract

Gastromermis deltensis n. sp., Hydromermis conopophaga Poinar, 1968, and Hydromermis palustris n. sp., parasites of chironomids (Diptera) in the Delta Marsh, Manitoba, Canada, are described and illustrated. The three species showed patterns of morphological variation, the most common being variation in ventral displacement of the mouth. This led to a reconsideration of the genera Gastromermis and Hydromermis. Spicule length is proposed as the differential characteristic between the two genera. Species placed to date in Gastromermis are reassessed on this basis.