Small larvae, up to 5.5 mm long.
Antenna with 5 segments; segments consecutively shorter or with segments 3 and 4 subequal in length. Ring organ on basal 1/4 of segment 1. Blade shorter than length of flagellum. Lauterborn organs between 1/2 and full length of segment 3. Style subequal to segment 3.
Labrum with SI basically bifid, with 2 unequal branches, each branch with few small points, giving appearance of weakly serrate seta; remaining S setae simple. Pecten epipharyngis of 3 scales, with median scale longer than outer pair. Labral lamellae absent. Chaetae serrate; spinulae simple. Ungula V-shaped, basal sclerite quadrate. Premandible with 1 apical tooth and a well developed inner tooth, brush present.
Mandible with apical tooth shorter than combined width of 3 inner teeth. Outer margin crenulate. Mola adjacent to seta subdentalis darkened, as inner teeth. Seta subdentalis apically notched, extending to innermost tooth. Seta interna with 7 serrate branches.
Mentum with median tooth broader than first of 6 pairs of lateral teeth and with apicomedian protuberance (nipple) absent with wear(?). Ventromental plate narrow; beard absent. Setae submenti at level of 5th lateral tooth.
Maxilla with pecten galearis.
Body with anterior and posterior parapods separate, each bearing an apical crown of claws. Procercus shorter than wide, bearing 6 apical anal setae. Anal tubules longer than posterior parapods. Body segment 4 with 1 pair of setal tufts, 5 with 2 pairs, and 8-11 with 4 pairs each.
The original description of Shilova and Zelentzov (1978) of the monotypic species Stackelbergina praeclara from northern Russia, was enhanced in the Holarctic keys (Cranston et al., 1983). Some inaccuracies in these works were rectified following the discovery in northern Québec (Barton et al., 1993).
The Russian populations were found as larvae in temporary bodies of water in Borok region, in May. The Québec population was found in rock pools and small ponds near the entrance of the Koroc River into Ungava Bay, northern Québec, just at the northern treeline. Pools are ice-free only from early June until late September. Waters were acidic, dark, and less than 40 cm deep. Sediments were fine organics and sand.