Large larvae, up to 14 mm long. Head capsule squarish in outline and with numerous closely spaced short setae; postoccipital margin with a long, ventrolateral, posteriorly-directed projection on each side.
With 4 segments; segment 3 shorter than 4 and both of them much shorter than segment 2; segment 3 not annulated. Style and Lauterborn organs longer than segment 3.
With all S setae short and simple. Labral lamellae consisting of a semicircular row of broad, leaf-like, overlapping scales, some apically serrate. Chaetae apparently absent, although lateral labral lamellae may be indistinguishable from chaetae; 3-4 pairs of spinulae present. Pecten epipharyngis consisting of 3 coarsely serrated to pointed scales, continuous with chaetulae laterales. Ungula short, rectangular; basal sclerite absent. Premandible narrow, straight with weak inner teeth; lateral spine absent.
Apical tooth longer than combined width of 5 inner teeth. Seta subdentalis pointed. Blunt projection present dorsal to seta subdentalis. Seta interna absent.
With anterior margin of middle 2/3 irregular, without teeth; 2 pairs of extreme lateral teeth present, outer lateral tooth pointed or bifid. Ventromental plate small. Seta submenti arising closer to mentum than to postoccipital margin.
With palp longer than wide. Flat, apically serrate scales present dorsal to palp (perhaps lamellae of gallae). Nine to 16 anterior setae maxillaris present; all simple.
With anterior and posterior parapods separate, each bearing an apical crown of long and narrow claws; some posterior parapod claws with fan-shaped serrated inner part. Procercus longer than wide, bearing 5 anal and 2 subapical setae. Anal tubules narrowly triangular, about 1/3 length of posterior parapods. Body setae pale.
Larvae of Protanypus are very distinctive in that the mental teeth are confined to the extreme lateral margins, the head bears numerous setae, and a pair of long distally-directed projections, and the M-appendage of the premento-hypopharyngeal complex is deeply divided into lamellae.
Larval Protanypus usually inhabit oligotrophic lakes.
The genus is Holarctic in distribution with at least 9 species.