Umingmakstrongylus pallikuukensis (Up) is a protostrongylid nematode which requires gastropod intermediate hosts (IH) for development from first-stage larvae (L1) to third-stage larvae (L3). Three captive muskoxen were infected with L3 of 'Up'. The prepatent period ranged from 91-95 days and patent periods extended at least 2 yr. Lung lesions were visible radiographically by 178 and 191 days post-infection (PI) and post mortem computed tomography was useful for locating and characterizing lung cysts. Cyst size was positively correlated with the number of adult nematodes contained. Lung pathology appeared restricted to the cysts. In the IH 'Deroceras laeve', most larval growth occurred following the second molt. Larvae developed more rapidly at warmer temperatures and the threshold temperatures were 8.5 C and 9.5 C in 'D. laeve' and 'D. reticulatum', respectively. The degree-days required for development, 167, were the same in both species. In the laboratory the majority of the L3 emerged from 'D. laeve ' and 'D. reticulatum' by 60 days PI and emergence occurred independently of the intensity of infection. L3 emerged from ' Catinella' sp, in the laboratory and 'D. laeve' under semi-natural conditions in the Arctic. Emerged L3 developed to adults in a captive muskox. Development rates of 'Up' in 'D. laeve' in enclosures in the tundra near Kugluktuk, Canada, corresponded with those predicted using surface microhabitat temperatures and laboratory derived threshold temperatures and thermal constants. Infected slugs overwintered on the tundra and first and second-stage larvae resumed development the following spring. This enclosure-model system could be used to investigate protostrongylids in other geographic regions or under different climatic conditions. In the mainland Arctic near Kugluktuk, Nunavut, the terrestrial gastropods: ' D. laeve; Columella alticola; C. edentula; E. fulvus; Vertigo' cf ' modesta'; and 'Catinella' sp., and the freshwater gastropods: ' Aplexa hypnorum; Physa jennessi jennessi; Valvata sincera helicoidea'; and 'Stagnicola' sp., were found. 'Deroceras laeve, A. hypnorum, Valvata' sp., and 'Stagnicola' sp., were also present on Victoria Island, Nunavut. Larvae developed to L3 in ' D. laeve, C. alticola, E. fulvus, Catinella' sp., and 'A. hypnorum '. From this research a model for the seasonal development and transmission of 'Up' in the Arctic is presented
