Medium-sized larvae, up to about 7 mm long. Body light brownish. Head capsule slender, elongate-oval; cephalic index 0.5-0.6. Dorsally, S5, DP, and S8 nearly aligned; S8 and S7 somewhat distant from each other, aligned laterally. Ventrally, S10 posterolateral to S9; VP larger than setal pits, closer to S10 than S9; SSm directly posterior, or poster-median to S9. SSm, S5 multi-branched to plumose, remaining setae simple.
Half as long as head, 3x as long as mandible. Antennal ratio 3.7-4.2. Basal segment about 10x as long as basal width, with ring organ at 0.55; segment 2 about 10x as long as wide; segment 3.5x as long as wide, 2x as long as last segment. Style as long as segment 3, broadened in apical 1/2. Peg sensilla large, 1/2 as long as segment 3. Blade and accessory blade somewhat longer than segment 2; basal ring about 4x as high as wide.
Gradually curved and narrowed towards apex. Apical tooth 2.5x as long as basal width, 1/3 length of mandible. Inner tooth, large, apically-directed, rounded, not projecting beyond margin of seta subdentalis; small accessory tooth projection dorsally on mola, near insertion of large, curved seta subdentalis; molar expansion weakly developed to very large and as long as basal width of apical tooth, with flat or long, apically-directed apex. Ventrolateral setae situated in close row on outer margin of proximal 1/2 of mandible; seta 1 very small; space between ring organ and seta 3 about 2x as great as that between setae 2 and 3.
Basal segment of palp 6x as long as wide, with ring organ at 0.7.
Without fringe of swim-setae. Anal tubules long and slender, almost 2x as long as posterior parapods. Supranal setae dark, situated on large, darkened tubercle, stronger and longer than anal setae. Subbasal seta of posterior parapod dark and more than 1/2 as long as posterior parapod. Procercus dark posteriorly, 6x as long as wide, with 7 brownish-black apical setae. Claws of posterior parapod either all simple; large claws with small spinules on inner and/or outer edge, 1 smaller claw slightly to strongly darkened, or (s.w. USA species) all claws simple, several small claws with lamellate outer section.
Pentaneura larvae are recognizable by very long anal tubules and large supraanal setae mounted on dark tubercles. The mandible has very large mola and inner teeth; in contrast to Trissopelopia, the ring organ is situated in the apical 1/3 of the basal maxillary palp segment. Unnamed material from North America with more weakly developed mola, and essentially straight inner teeth of the ligula extends the larval generic diagnosis (M. Bolton pers. comm.).
Larvae of Pentaneura occur in small and large bodies of running water.
The known distribution of the genus is North and South America, with 2 species on each continent. Pentaneura inconspicua and P. inyoensis are quite common throughout the USA in rivers and streams. Epler (2000) discussed unnamed material from North America that extends the generic diagnosis. Unnamed Pentaneura are known from Guatemala (Sublette and Sasa, 1994) and from Costa Rica (Watson and Heyn, 1999). In South America, the type species, P. cinerea, is known from Argentina and Chile, and this, or P. elisae, may be an unidentified species reported from Patagonian rivers. Two pupal forms are reported from Argentine Patagonian streams (Garcia and Suárez, 2007).