Medium-sized larvae, up to 10 mm long. Posterior margin of head dark brown; body yellowish white. Head capsule longish, oval; cephalic index 0.7. Dorsally S5 anterior to DP; S5 located very mesially and DP remote from approximated S7, S8. Ventrally S9, S10 and VP closely grouped, with S10 similar size to S9, S10 lateral or posteromesial to S9; SSm located more distant and mesially than in relatives.
2.5x as long as mandible, 1/2 as long as head. Antennal ratio about 5.0. Basal segment about 11x as long as basal width, tip oblique, with ring organ between 0.4 and 0.6; segment 2 about 9x as long as wide; segment 3 only slightly longer than terminal segment. Style extending to middle of terminal segment, club shaped. Peg sensilla small. Blade as long as flagellum; basal ring 2.5x as high as wide. Accessory blade extending to region of terminal segment.
Apical 1/2 strongly tapered, about 3x as long as wide; basal 1/2 considerably broadened. Apical tooth 2x as long as basal width, 1/4 length of mandible; distal 1/2 blackish brown. Bluntly rounded, easily distinguished inner tooth, somewhat overlying the seta subdentalis; mola scarcely produced, apically directed. Ventrolateral setae situated on outer margin of basal 1/2 of mandible, sensillum minusculum proximal thereto; setae 1 and 2 located very close together, seta 3 halfway between 1 and Ring organ; seta 1 small, scarcely noticeable peg, 2 simple, 3 divided.
Basal segment of palp 3.5x as long as wide, with ring organ at 0.8; b seta 2-segmented, basal segment 3x as long as apical segment.
Without fringe of swim-setae. Anal tubules slender, spindle-shaped, about 5x as long as wide. Subbasal seta of posterior parapod simple. Procercus 3x as long as wide, with 7-9 anal setae. Claws of posterior parapod simple; larger claws in part with small spines on inner and/or outer margin; some smaller claws may be darkened relative to remainder.
Arctopelopia belongs in the tribe Pentaneurini, to the Thienemannimyia-group of genera. It may be distinguished with difficulty from genera with the 2-segmented maxillary b sensillum by the strongly broadened middle section of the pseudoradula and the many (about 25) teeth on pecten hypopharyngis.
Larvae of Arctopelopia inhabit small and large oligotrophic standing water bodies, where most species are cold stenotherms (except A. griseipennis). Arctopelopia larvae are the most abundant Tanypodinae in arctic and subarctic lakes. Vallenduuk and Moller-Pillot (2008) discuss their notably more diverse ecology in the Netherlands. One species is described from the Nearctic, two or three others are known from pupal skins and three species are known from the Palaearctic. Arctopelopia barbitarsis, A. melanosoma and A. griseipennis are distributed from arctic northern to central Europe as far south as the Pyrenees. Arctopelopia griseipennis may have a broader range, extending to Greenland and crossing the Alps into Italy. The sole Nearctic species, A. cana has a restricted distribution in northern Canada.