Small to medium sized larvae, up to 7 mm long.
Antenna with 5 segments; segment 3 and 4 subequal in length or 4 longer than 3. Ring organ on basal 1/4 of segment 1. Blade subequal in length to flagellum. Lauterborn organs distinct, from 1/2 to about as long as segment 3. Style well developed, usually as long as segment 3.
Labrum with SI weakly branched to plumose; remaining S setae simple. Labral lamellae absent. Chaetae serrated; spinulae simple. Pecten epipharyngis consisting of 3 scales. Chaetulae laterales simple to serrate; chaetulae basales apically weakly branched. Ungula with elongate basal sclerite. Premandible with 1 apical tooth, sometimes weakly notched; brush absent.
Mandible with apical tooth shorter than combined with of 3 inner teeth. Seta subdentalis peg-like. Seta interna with about 6 smooth or serrate branches. Mola with 2-3 simple spines.
Mentum with 1-2 median teeth and 5 pairs of lateral teeth. Ventromental plate narrow; beard absent. Sclerotization of mentum not uniform, with irregular longitudinal bands of dark sclerotization alternating with lighter bands, thus appearing striated.
Maxilla with palpiger with triangular lamellae. Galea with chaetoid lamellae and pecten galearis. Setae maxillaris simple.
Body with procercus at least 1.5 times as long as wide, strongly sclerotized and bearing 5-8 anal setae. Supraanal setae well developed. Anal tubules shorter than posterior parapods. Body setae strong, each segment with setae at least 1/2 segment length.
Larval Tvetenia are distinguished from those of the closely related Eukiefferiella by the long body setae, well-developed procercus and subdivided SI setae (difficult to see on many specimens). Tvetenia is equivalent to the Eukiefferiella discoloripes group of earlier workers.
Larval Tvetenia inhabit flowing water in the Holarctic, Afrotropical and Oriental regions with about seven species in the Holarctic region.