Biogeography of helminth parasitism in Lemmus Link (Arvicolinae), with thedescription of Paranoplocephala fellmani n. sp (Cestoda : Anoplocephalidae) from the Norwegian lemming L. lemmus (Linnaeus)

We describe the gastrointestinal helminth fauna of true lemmings (Lemmus sp p., Arvicolinae) based on published and original material throughout the Ho larctic range of these hosts. According to the existing data, the helminth fauna of true lemmings consists of three widespread and/or locally common t axa: Hymenolepis horrida (sensu lato) (Hymenolepididae), Anoplocephaloides lemmi (Anoplocephalidae) and Heligmosomoides spp. (Heligmosomidae). Despite the taxonomic boundaries and ancient phylogenetic splits in the hosts, the re are no major faunistic differences for parasites within western (Siberia n) L. sibiricus and L. bungei, and eastern (North American) L. trimucronatu s throughout their distribution range. In contrast, the Norwegian lemming L . lemmus, which is a Fennoscandian endemic and closely related to the weste rn populations of L. sibiricus, has only a single host-specific helminth, t he cestode Paranoplocephala fellmani n. sp. (Anoplocephalidae). We describe the new species and show that it differs consistently from related species by its long and slender cirrus-sac. However, there are also a number of ot her significant differences, e.g., P. fellmani n. sp. and Andrya primordial is in Tamiasciurus hudsonicus (Sciuridae) evidently have a unique (sub)type of uterine development among Andrya/Paranoplocephala spp. Because P. fellm ani n. sp. was also found to occur in Alaska (host L. trimucronatus), this species seems to follow the same biogeographical pattern as the other speci alist helminths of Lemmus. We suggest alternative explanations for the abse nce of three major helminth taxa in the Norwegian lemming in Fennoscandia.