Medium sized larvae, up to 8 mm long.
Antenna with 4 or 5 (usually) segments; segments consecutively shorter or segments 3 and 4 subequal in length; occasionally antenna very short. Ring organ on basal 1/3 of segment 1. Blade shorter than length of flagellum. Lauterborn organs usually distinct, sometimes vestigial or absent. Style shorter than length of segment 3.
Labrum SI usually bifid, rarely simple; remaining S setae simple. Labral lamellae absent. Chaetae simple or serrate; spinulae simple, weak. Pecten epipharyngis consisting of either 3 scales [in Cricotopus s.str. and C. (Nostococladius)] or a single scale [in C. (Isocladius)]. Chaetulae laterales variable in number and shape; sometimes in C. (Isocladius) first pair subequal in size to scale of pecten epipharyngis and could be mistaken for lateral scales of pecten epipharyngis; chaetulae basales with branched apices. Ungula generally U-shaped with short basal sclerite. Premandible with 1 or, rarely, 2 apical teeth; brush present or absent, weak when present.
Apical tooth shorter than combined width of 3 inner teeth. Seta subdentalis apically pointed or notched with a hook. Seta interna usually present and consisting of 6-7 simple or finely serrate branches, rarely absent. Outer margin usually crenulate, sometimes smooth in C. (Nostococladius) sometimes several flat tooth-like projections present. Mola usually smooth, sometimes spines present.
One median and 6, rarely 5 or 7, pairs of lateral teeth present. Ventromental plate narrow; beard absent.
Maxilla palpiger with triangular chaetulae. Lamellae of galea variable, usually dorsal pectinate lamellae present in C. (Cricotopus); pecten galearis absent. Setae maxillaris simple.
Body with separate anterior parapods, each bearing an apical crown of claws; sometimes claw with a distinct apical tooth. Posterior parapods separate, each with an apical group of simple claws. Procercus about as high as wide, bearing 6-7 anal setae. Anal tubules vary in length, usually shorter than length of posterior parapods. Abdominal segments usually with 1 pair of setal tufts, sometimes only simple setae present.
Larval Cricotopus occur in all types of water bodies, including some saline and coastal waters. Larvae are associated frequently with aquatic macrophytes, algae and sometimes cyanobacteria (Nostoc). Some larvae mine in macrophytes, many graze on the surfaces.
Subgenus C. (Nostocladius) is associated with Nostoc colonies; s.g. C. (Isocladius) is somewhat more common in standing waters, Cricotopus s.s. in flowing waters. Hirvenoja (1973) revised the western Palaearctic species, of which some species are present in North America, otherwise the fauna is less well known. A diverse Australian fauna includes only the nominate subgenus.