Head capsule about 1.75 as long as wide, somewhat wedge shaped. Eye in two adjacent parts, posterior larger than anterior.
Antenna about 1/3 as long as head capsule; basal segment about twice as long as flagellum, with ring organ 1/3 from base and 2 setae about at 2/3; antennal segment 2 slightly longer than combined length of 3-5. Lauterborn organs well developed, style weak. Blade shorter than flagellum.
Labrum with S I apparently bifid (perhaps sometimes simple) and S III apparently weak and simple; S II [labral seta S I in Sæther (1981), see Epler & de la Rosa (1995)] strong, situated on tubercle; at least 3 chaetae. Pecten epipharyngis of 3 simple spines. Chaetulae laterales 4-6 pairs, chaetulae basales apically bifid. Premandible simple, with well developed brush.
Mandible with 4 inner teeth, apical tooth slightly shorter than combined width of first 2 inner teeth, seta interna with about 7 plumose branches.
Mentum with 3 median teeth, subequal in size with median either level or recessed; with 5 pairs of lateral teeth of which the first is adpressed to outer of the median teeth. Ventromental plates narrow, broader posteriorly. Setae submenti situated well posterior to base of outer lateral tooth of mentum.
Maxilla with long lacinial chaetae.
Body setae dark and strong. Claws of anterior parapods serrate. Procercus higher than wide, with 3-4 anal setae. Posterior parapods long, more than 5x as long as medially wide. Sub-basal seta well developed, simple or (Arizona O. semifimbriata) apically trifid. Anal tubules much shorter than posterior parapods.
The larva of Onconeura has an antenna about 1/3 the length of the head, as opposed to 1/4 in Tempisquitoneura, about 1/2 to 3/4 in Thienemanniella, and about as long as the head in Corynoneura. The S I either is simple or bifid as in Tempisquitoneura and Notocladius. Separation of larvae of these genera is not certain, but seemingly Onconeura has much stronger and darker body setation than others in the group.
Onconeura was described first from the Caribbean (as a Thienemanniella), and subsequently recognised from Mexico, for the type-species O. fimbriatus (Sæther). On pupal evidence particularly, diversity is high throughout meso- and south America (Wiedenbrug et al, 2009). An Onconeura identified as the type species is quite widespread in flowing waters of Arizona and New Mexico, where it tolerates high temperature, elevated conductivity and sediment in riffles (Krestian et al., 2009) . Larvae of Brazilian species were found free-living in both litter and on the surface of stones in streams, and are colonists of artificial substrates (Wiedenbrug et al, 2009).