Description and morphometric variability of Paranoplocephala serrata n. sp(Cestoda : Anoplocephalidae) in collared lemmings (Dicrostonyx spp., Arvicolinae) from Arctic Siberia and North America

We describe Paranoplocephala serrata n. sp. (Cestoda, Anoplocephalidae) fro m collared lemmings Dicrostonyx torquatus and D. groenlandicus (Arvicolinae , Rodentia) in Arctic Siberia and North America. The new species was record ed from the Yamal Peninsula (type-locality), Yana Delta, Kolyma Delta, Wran gel Island, Alaska and Victoria Island/Kent Peninsula (Northwest Territorie s). P. serrata n. sp. is characterised by a long, ribbon-like strobila, dis tinctly serrated segments, a small scolex, unilateral or infrequently alter nating genital pores and testes confined to the antiporal part of the segme nt. It differs from the related species (Andrya bairdi, Parandrya feodorovi and Paranoplocephala maseri) by several morphological features, including the distribution of testes (several testes antiporal to ventral longitudina l osmoregulatory canal), structure of the cirrus-sac and vagina, and large eggs (0.053-0.068 mm in the type-material). The material of P. serrata n. s p. from North America differs from the Siberian material by the shorter cir rus-sac, smaller dimensions of the female reproductive organs, larger semin al receptacle and larger eggs. However, the statistical differences in the dimensions of reproductive organs mainly reflect the larger size of mature segments in Siberian specimens compared with North American specimens. The main diagnostic features, i.e. the size and form of scolex and suckers, num ber and distribution of testes, position of female glands, vagina/cirrus-sa c ratio and morphology of reproductive organs, do not differ markedly betwe en the Palaearctic and Nearctic specimens. According to the structure of th e early-stage uterus, A. bairdi Schad, 1954 belongs to the genus Paranoploc ephala. Parandrya Gulyaev & Chechulin, 1996 is probably a synonym of Parano plocephala. A redescription is provided for Paranoplocephala bairdi n. comb .