Small larvae, up to 4 mm long.
Antenna about as long as length of head capsule; mounted on pedestal. Segmentation unclear but apparently 4 segmented with segment 2 longer than first. Ring organ on basal 1/2 of segment 1. Blade long, ending before apex of flagellum. Lauterborn organs very large, arising at different levels on basal 1/3 of segment 2. Style long, arising on basal 1/3 of segment 2.
Labrum with SI plumose; remaining S setae simple with SII long and blade-like; sockets of SI and SII distinctly raised. Labral lamella consisting of a single oval scale abutting sockets of SI. Chaetae simple to weakly branched apically; spinulae simple, elongate. Pecten epipharyngis consisting of 3 small scales. Chaetulae laterales simple to serrate; chaetulae basales simple. Ungula U-shaped; basal sclerite absent. Premandible with 4 teeth; brush absent.
Apical tooth shorter than combined width of 3 inner teeth. Seta subdentalis long, with narrowed and pointed apex. Seta interna with 7 plumose branches.
Mentum deeply recessed medially with 2 median and 6 pairs lateral teeth; first lateral teeth shorter than lateral teeth; third to sixth lateral teeth sloping distolateral from second lateral teeth. Ventromental plate large; without beard.
Maxilla with palpiger with triangular chaetulae. Galea with simple to pectinate lamellae; pecten galearis absent. Setae maxillaris simple.
Body with anterior parapods separate, each with an apical and subapical group of claws. Posterior parapods separate, each bearing an apical crown of claws. Procercus longer than wide with 6-8 anal setae; proximal subapical setae often long. Anal tubules shorter than length of posterior parapods. Body setae simple.
The larvae of Heterotanytarsus predominantly occur in standing waters: oligotrophic lakes and ponds, including humic waters. They may be found in some flowing waters. Larvae live in free tubular cases, in which pupation occurs. Four species are described, all from the Holarctic region.