Small larvae, to 3 mm long.
SIII simple, bifid, or weakly plumose.
Antenna with 5 segments on prominent pedestal bearing pronounced apical spur. Antennal ratio c 1.0-1.3. Ring organ and weak seta proximal on 1st antennal segment. Segment 2 longer than 3rd segment, and alternate well-developed, large Lauterborn organs sessile or placed on short pedestals, proximal Lauterborn organ arising mesally on basal 1/2 of 2nd segment, the other distal. Long style distal on segment 2. Antennal blade inserted apically on 1st segment, extending beyond antennal apex; accessory blade fused to base of blade, short.
SI seta comb-like, fused at base, SII plumose, situated on large pedestal. SIII short, simple, SIVa present. Labral lamellae well developed. Pecten epipharyngis consisting of 3 separate, slender, triangular scales. Premandible with 2-3 slender apical teeth and broad basal tooth brush strong.
Mandible with pale dorsal tooth, apical tooth and 3 pointed inner teeth brownish. Seta subdentalis long, curved, reaching beyond apical tooth. Seta interna of 4 strongly plumose branches. Pecten mandibularis well developed with several strong lamellae, of which the outermost is particularly strong and may appear as an extra outer mandibular tooth.
Mentum with rounded, median tooth and 6 pairs of yellow or darker laterals, regularly decreasing in size; first pair may appear fused with median Ventromental plates fan-shaped, widely separated medially, subequal in width to mentum, anterior margin smooth.
Without tubules. Claws of posterior parapod simple.
Stempellinella larvae can readily be separated from all other genera, with the exception of Zavrelia, by the fact that one Lauterborn organ arises proximally and the other distally on antennal segment 2. They differ from Zavrelia larvae in the form of the pecten epipharyngis, which consists of 3 elongate triangular scales, and in the form of the premandible, which has 2-3 teeth weakly inclined to main axis, whereas in Zavrelia there are 4 teeth all inclined at about 90° to main axis.
Brundin (1948a) distinguished larvae of Stempellinella from those of Zavrelia principally on slight differences in the antennae. On the basis of the material presently available these differences appear to be invalid. Although the two genera are clearly very close, they can be separated by the form of the pecten epipharyngis and on the shape and arrangement of teeth on the premandible.
Larvae of Stempellinella occur in springs and small streams as well as in lakes. Larvae construct transportable cases, which differ from those of Stempellina in being straight and parallel-sided.
The genus is Holarctic in distribution with seven named species, most without definitely associated larvae. Undescribed species occur in s.e. Asia, including East Timor, and tropical northern Australia.