Medium-sized larvae, up to 8 mm long. Head brown; body greenish-brown to brown; antennal segment 2 dark brown; claws darkened. Head capsule slender; cephalic index 0.45-0.50. Dorsally S5 posteromesial to S7 and S8, S8 anteromesial to S7, DP absent. Ventrally S9-S10-SSm forming curved line, VP narrowly oval, not aligned.
Antenna 1/2 as long as head, 3x as long as mandible. Antennal ratio about 3. Basal segment 11x as long as basal width, with ring organ at 0.6; segment 2 8x as long as wide; segment 3 2.5x as long as wide, somewhat longer than last segment. Style large, clubbed apically, extending to middle of segment 4. Peg sensilla large, longer than segment 3, tightly fused with margin of segment 2, resembling tuning fork. Blade as long as segment 2; basal ring 1.5x as high as wide. Accessory blade reaching to end of segment 3.
Strongly curved, gradually tapered towards apex. Apical tooth 2.5x as long as basal width, somewhat less than 1/4 length of mandible, with flat lamella on dorsal inner margin at base of apical tooth; large, distally-directed inner tooth inclined ventrally; mola strongly protruding, blunt-ended; seta subdentalis strong. Ventrolateral setae and ring organ aligned on outer margin of proximal 1/2 of mandible.
Basal segment of palp somewhat curved, 3.5x as long as wide, with ring organ at 0.7.
Without fringe of swim-setae. Anal tubules spindle-shaped, 4x as long, as wide. Procercus 3.5x as long as wide, with 7 apical setae. Claws of posterior parapod variable in shape and colour; larger claws with small, fine points on inner and/or outer margin; 1 large claw dark, others dark with larger spines on inner margin; 4 small claws with coarse inner spineless, 1 with comb.
Xenopelopia resembles Telmatopelopia among the group of genera with a tuning fork-like arrangement of Lauterborn organs. In Xenopelopia, the middle tooth of the ligula projects distinctly beyond the otherwise straight row of teeth. The pseudoradula is more strongly broadened basally than in Telmatopelopia; in Monopelopia it is uniformly broad. The dark antennal segment 2 and some claws is distinct from the pale condition in Telmatopelopia, as is the antennal ring organ being somewhat distal to the middle. The alignment of ventral SSm-VP-S10-S9 into a transverse curve in Telmatopelopia differs in Xenopelopia in which VP-S10-S9 are more longitudinally aligned, with SSm medial.
The larvae of Xenopelopia live in a variety of small water bodies and in the littoral of eutrophic lakes. Both European species colonise short-lived pools [e.g. all artificial pools created a Scottish freshwater marsh (Jefferies, 1989), but lack adaptive strategies to survive drought (Dettinger-Klemm and Boehle, 1996)].
The genus is Holarctic, with X. tincta from western North America and X. falcigera and X. nigricans known from the western Palaearctic. Subfossil head capsules potentially belonging to Xenopelopia are reported from West Africa lakes (Eggermont et al., 2005) although no species are allocated to this genus from the modern Afrotropical fauna.