Small larvae, up to 3 mm long.
Antenna at least 1/2 but no more than 3/4 length of head; 5 segmented; segment 3 unusually long; segments 4 and 5 small. Segment 3 is frequently darkened except in T. fusca where this segment is shorter than usual and pale. Mark of insertion of seta distinct on segment 1. Blade short. Lauterborn organs small.
Labrum with all S setae weak and simple; well developed seta on tubercle may be either labral seta SI or SIVa. Pecten epipharyngis consisting of 3 triangular spines; first pair of chaetulae laterales broad and serrate; chaetulae basales either present or apparently absent. Premandible with 1 apical tooth and distinct, long brush.
Mandible with apical tooth subequal to first of 4 inner teeth. Seta subdentalis weak or absent. Seta interna with 6 plumose branches.
Mentum with 2-3 median teeth and 5 pairs of lateral teeth. Ventromental plate poorly developed, without beard beneath.
Maxilla with small sensillae on palp, larger sensillae on galea. Galear surface with many fine setae; possibly divided lamellae. Seta maxillaris finely serrate. Pecten galearis and appendix absent.
Body with meso- and metathoracic segments fused; only 2 thoracic segments present. Anterior and posterior parapods separate and bearing claws. Procercus small and bearing apically 4 or 5 setae. Anal tubules pointed and shorter than posterior parapods. A strong, simple, somewhat darkened seta arises from ventral basal half of posterior parapods. One species, T. fusca, has numerous stout setae on body; remainder have only short, pale setae at most.
Thienemanniella shares with Corynoneura the modified chaetulae laterales and labral setae, fused meso- and metathoracic segments, ventrobasal spine on the posterior parapod as well as elongate antennae. Thienemanniella differs from Corynoneura in the 5 segmented antenna (4 in Corynoneura).
Thienemanniella larvae are found in most lotic habitats from fast mountain streams to slow moving ditches and lowland rivers. Both Thienemanniella and Corynoneura larvae are found frequently in interstices in submerged stones and wood, where their small size may allow them to resist high water flow.
Thienemanniella is understudied on account of its small size, and true diversity is probably high.