Medium-sized to large larvae, up to 8 mm long. Head yellowish-brown; body greenish yellow with brownish spots. Head capsule longish, oval; cephalic index 0.6. Dorsally, S5, DP, S8 and S7 almost aligned; DP almost lateral to S5; S8 pit smaller than S7. Ventrally VP eye-shaped, bigger than setal sockets, aligned to SSm-S10. Setae simple.
Somewhat less than 1/2 as long as head, 2.75x as long as mandible. Antennal ratio 3.4-4.0. Basal segment about 13-15x as long as basal width, with ring organ at 0.6-0.7; segment 2 about 15x as long as wide; segment 3 about 7x as long as wide, about 1/3 shorter than last segment. Style extending to middle of last segment. Peg sensilla almost 1/2 as long as segment 3. Blade about equal in length to segment 2; basal ring 3x as high as wide. Accessory blade as long as flagellum.
Slender, gradually and slightly curved, apical 1/2 strongly narrowed. Apical tooth 2.5x as long as basal width, 1/4 length of mandible. Inner tooth large, distally directed, apically rounded, extending to seta subdentalis; mola large, bluntly rounded apically; seta subdentalis long extending to near apex of mandible. Ventrolateral setae aligned in proximal 1/2 of mandible; seta 1 with small pit, not obvious, setae 2 and 3 simple, long; ring organ situated proximal to seta 3, further removed than seta 2 is from seta 3.
Basal segment of palp elongate, 4-5x as long as wide; ring organ about 0.5.
Without fringe of swim-setae. Anal tubules 1/2 as long as posterior parapods, 4.5x as long as wide. Procercus pale, 2.5-3.5x as long as wide, with 7 light brown apical setae. Claws of posterior parapod simple; large claws with small spinules on inner and/or outer margin; outer margin of some small and medium-sized claws with basal 1/2 flattened into lamella
Trissopelopia in the tribe Pentaneurini seems related to Pentaneura. However the unusually narrow mandible and slender maxillary palp, in conjunction with the outer margin of some smaller claws being flattened into a lamella distinguish the genus.
Larvae of Trissopelopia live especially in groundwater-fed springs, mountain brooks and in northern latitudes, in the littoral of lakes. They are cold stenothermic and polyoxy biontic.
The genus is represented in the Palaearcic by T. flavida and T. longimana, both widespread from Europe to Japan, where T. oyabetrispinosa also occurs. Trissopelopia ogemawi is known from Alberta to Québec, south to the Carolinas and Georgia (Epler, 2001), and a different, undescribed larva has been found in an Arizona rheocrene. The genus is reported from Nepal (Roback and Coffman, 1987) and from Oriental China (Cheng and Wang, 2005). Outside the northern hemisphere there are records of Trissopelopia from the Afrotropical region, and pupal exuviae have been collected in low order streams in central São Paulo state, Brazil (Siqueira and Trivinho-Strixino, 2005).