Intra‐specific variability of the morphology in a single population of the seal parasite <i>Contracaecum osculatum</i> (Rudolphi) (Nematoda, Ascaridoidea), with a redescription of the species

Abstract

Contracaecum spp. are common parasites of seals and piscivorous birds. The world‐wide distribution which has been attributed to the species C. osculatum needs verification. In the present study thc intra‐specific variability of some taxonomically significant characters was studied in this species. Features analysed include the length and morphology of the distal end of the spicules, the number of proximal caudal papillae and the number of papillae in the region of the first 25 cuticular transverse striae anterior to the cloaca, delined as the Pts zone (precloacal transverse striae zone). The spicules reach their maximum length only in fully grown worms. while the morphology of the distal end of the spicule is determined early in the life of adult male worms. Included is a detailed analysis of the observed morphometric variability in the distal end of the spicule. The number of cuticular transverse striae in relation to papillae in the Pts zone remains constant in different length classes of the parasite. A redescription of the parasite is provided, bascd on material obtained from grey seals in the Baltic Sea, to serve as a basis for discussions on the taxonomy of the genus.