The value of cuticular fine structure in identification of juvenile anisakine nematodes

Juveniles of the ascarid nematodes Anisakis sp. and Phocanema sp. from marine teleosts, have been implicated as major causative agents of human anisakiasis. Whereas juveniles of the related genus Thynnascaris sp. have not been reported from humans, this nematode may occur in fish concurrently with the aforementioned species. The juvenile anisakine nematodes are not readily identified, and reliable morphological markers would provide a valuable aid in identification of potentially pathogenic individuals. In this study of cuticular fine structure, the following characteristic difference appeared to be most significant: a wide electron lucent area containing partitions and previously unreported electron dense rods occurred in the basal layer of the Phocanema sp. cuticle, but not in that of Anisakis sp. or of Thynnascaris sp. Juveniles of Thynnascaris sp. possessed a cuticle that was structurally similar to that of Anisakis sp., but only about one-half as thick. Comparatively, the third stage Ascaris lumbricoides cuticle was poorly developed, and less definitively layered than those of the anisakines.