Small larvae, head capsule up to 0.30 mm long.
Antenna shorter than mandible; 6 segmented; segment 3 shorter than 4; ultimate segment vestigial and hair-like. Blade about as long as segment 2 or 2 and 3 combined. Lauterborn organs well developed. Style apparently short.
Labrum with SI simple (S. clinopecten) or with few apical teeth (S. montanus); other S setae simple. Pecten epipharyngis consisting of 3 weak spines. Chaetulae laterales simple; chaetulae basales notched apically. Premandible with simple apical tooth; brush absent.
Mandible with apical tooth longer than combined width of 3-4 inner teeth. Seta subdentalis broad. Seta interna with 4 serrate branches.
Mentum with one broad median tooth with indication of double median nipple, taller than the first 5-6 pairs of lateral teeth; median tooth, either median tooth alone or median plus first lateral tooth joined to ventromental plate, forming distinct ventromentum. Ventromental plates very broad, extending past outermost teeth on flattened mentum, with beard of 4-6 weak setae either underneath or slightly laterad.
Maxilla with small palp. Pecten galearis present. Anterior lacinial chaetae shorter and broader than other chaetae.
Body with anterior parapods at least partially divided ("normal" in S. montanus) with numerous claws. Posterior parapods well developed, with strong claws. Procercus also well developed, with 5 anal setae. Anal tubules present. Body setae simple, none conspicuous
Stilocladius was described on the basis of the adult male and pupal exuviae of Stilocladius montanus from the Italian Alps and Apennines (Rossaro, 1979). The genus was recognized for all stages of a 2nd species, S. clinopecten, from the Carolinas (eastern USA) (Sæther, 1982). Rossaro (1984) then found the larva and female stages of the Italian S. montanus, allowing expansion of the generic diagnosis presented by Cranston et al. (1983) in the Holarctic keys.
Larval Stilocladius occur in cold running waters in the Italian Alps, and are reported also in Europe from glacial tarn lakes in the Czech Carpathians. The range of the eastern USA species S. clinopecten has extended more widely in eastern USA, and a pupal exuviae from the Sierra Nevada mountains of California clearly belongs to the genus, if not the species (Cranston, unpublished). In the USA the genus has been found in cool, but not necessarily very cold, running waters. Yamamoto (1996) recognised Eukiefferiella kurobekeyakius as a 3rd member of the genus Stilocladius, from Japan.