[Morphological variability of thorny-headed worms of the genus Neoechinorhynchus (Acanthocephala: Neoechinorhynchidae) that parasitize fishes of the Arctic Ocean province in the boundaries of the USSR].

Study of the morphology of 602 specimens of N. rutili (Müller, 1780) and N. crassus Van Cleave, 1919 collected in 10 species of fishes from waterbodies of the Kola Peninsular, the Ob, Yenisei, Lena, Kolyma and Chauna rivers has shown that all absolute specific characters considered (13 in female and 17 in male) have a considerable range of variations due to the modificational individual and age variability. Differences have been revealed in morphometric indexes of some characters in members of the European and Siberian populations of N. rutili that is due to a geographic variability of the species. It has been established that most constant characters of all species studied are the length of the proboscis and its hooks.