Rhyssocolpus arcticus n. sp. (Nematoda: Nordiidae) from Ellesmere Island and a Redescription of Lindseyus costatus Ferris and Ferris, 1973 (Nematoda: Roqueidae) from Quebec, Canada.

A new species of Rhyssocolpus from Ellesmere Island in the Canadian arctic is described and illustrated. Its distinctive features are the set off head and the extensively striated cuticle in the vulval area with well-developed vulval flaps. The male has small spindle-shaped sperm 4-5 mum in length, and the adanal supplement is separated from the anterior series of 7-11 supplements by a distinct gap. A key to the species of Rhyssocolpus is provided. Lindseyus costatus from the St. Lawrence River, Quebec, is also redescribed. Notable differences from the original description are the irregular muscle bands of the sinistrally spiraled esophageal sheath, smooth exocuticle, longer prerectum, shorter male tail, and longer spicules. New information on the esophageal gland nuclei and sperm size and shape is also provided.