Medium sized larva, up to 7 mm long. Head brownish; body pale to slightly red, with brownish spots. Head capsule longish; cephalic index 0.52. Dorsally DP absent; S5 slightly posterior to S8, S7 clearly anterolateral to S8. Ventrally S9-S10-VP-SSm forming strongly curved line; VP bigger than setal sockets. Setae S5, S7 plumose, others ? simple.
Almost 1/2 as long as head, rather more than 2x length of mandible. Antennal ratio 3.0. Basal segment about 8x as long as basal width, with ring organ at 0.45-0.5; segment 2 about 6.5x as long as wide, widened at base; segment 3 2x as long as wide, about as long as last segment. Style clubbed distally, extending beyond middle of last segment. Peg sensilla large, as long as segment 3 and tightly fused to margin of segment 2, resembling tuning-fork. Blade not extending beyond segment 3; basal ring 2.5x as high as wide. Accessory blade somewhat longer than blade.
Strongly curved, gradually narrowed towards apex. Apical tooth almost 3x as long as basal width, 1/4 length of mandible. High, smooth lamella ventrally at base of apical tooth; inner tooth very large with apex curved distally, extending over seta subdentalis; mola distended into large tooth; seta subdentalis large. Ventrolateral setae situated in row on outer margin, in distal 1/3 of basal 1/2 of mandible; ring organ situated proximal to seta 3 and as far from seta 3 as the latter is from seta 1.
Basal segment of palp as long as wide; ring organ at 0.65.
Without fringe of swim-setae. Anal tubules about 3x as long as wide, as long as width of posterior parapod. Procercus about 3x as long as wide, with 7 apical setae. Claws of posterior parapod all yellowish, pale; 4 of smaller claws with several large teeth on inner margin, outer margin with low lamella; inner and/or outer margin of some larger claws with large spines.
Telmatopelopia belongs to the Pentaneurini in the group of genera with peg sensilla attaching to antennal segment 2 resembling a tuning fork. In common with Xenopelopia, the ligula teeth ends in a straight or weakly convex row: the two genera are quite similar in many features, including the strongly broadened base of the ligula, but may be distinguished by the pale antennal segment 2 and claws in Telmatopelopia and the antennal ring organ lies proximal to the middle of the 1st segment. The transversely curved alignment of SSm, VP, S9 and S10 is distinctive.
Larvae of the single species, T. nemorum, live in small water bodies of the western Palaearctic. Moderately acid pools in deciduous woodland- and marginal waters of boggy regions are favoured, where the species may attain high population densities. Reports of '?Telmatopelopia’ from Australia do not belong to the genus, but to a somewhat similar unreared and undescribed taxon.