Sturhan, 1981 (Nematologica 27:306-314) considered the tail terminus character, smooth in G. arcticus and annulated in G. tenuidens, the only reliable distinguishing character to separate these species. Alaskan populations designated G. arcticus based on average stylet and spicule length, 35 um and 25um respectively, have partially or completely annulated tails. Blocks on the cuticle are generally confined to the anterior region where they range from conspicuous to absent. SEM of face views consistantly show fewer head annules than G. longus and a more regular pattern around the perioral disk.