Small to medium-sized, 3-8 mm long, generally brownish, less often greenish, bluish or white, never red. Sometimes distinctly slender; length: width 9:1 to 17:1. Head somewhat longish, at most 1/4 longer than broad. On each side 1 more or less compact eye spot or 1-2 small eye spots anterior to a larger one.
Well developed, non-retractile, 4 or more usually, indistinctly-5 segmented; ultimate and penultimate segments may be short, segment 3 often with annulations that may extend onto indistinct 4th segment. Lauterborn organs poorly developed, shorter than style, or absent.
SI and SII setae strongly enlarged, sickle-shaped, ventrally situated on marked pedestals; SIII close together near to SI, either slender or, more generally, sickle-shaped and subequal to SI and II; SIVa either a normal seta or rod-formed and situated on a pedestal, SIVb similar but never on a pedestal; rarely there seems to be only 1 simple SIV seta on each side. Chaetae vary in number, size and form. Posterior to seta premandibularis is a labral rod. Spinulae present. Pecten epipharyngis consisting of 3-5 spines, free or more or less fused basally. Premandible absent.
With outer margin strongly bent medially. With 6-11 teeth, normally 11 small subapical outer tooth, 1 large apical tooth, and 4-9 smaller inner teeth. Seta interna a broad brush with numerous long branches.
With simple median tooth, sometimes with nipple, and 7-15 pairs of lateral teeth. Ventromental plates vestigial to indistinguishable.
Parapods always well developed, with simple or apically slightly serrate claws in apical crown; anterior parapods fused basally with divided apex. Procercus often long (up to 10x as long as broad and cylindrical, possibly globular; with anal setae ranging from very few, short to several, elongate. Supra-anal seta absent. Anal tubules 2 pairs, variable in length relative to posterior parapods. Anal end often directed posteriorly, sometimes part ventrally. Body without sclerotised plates; setae simple, usually pale, short and indistinct.