Large larvae, up to 16 mm long. Head capsule strongly sclerotized.
Dorsal head with clypeus narrowly separated from frontal apotome. Head capsule setae simple.
Antenna with 5 consecutively shorter segments; segment 1 weakly curved. Ring organ on basal 1/3 of segment 1. Blade longer than flagellum. Lauterborn organs and style about 3/4 as long as segment 3.
Labrum with labral sclerites SI 1 and SI 2 separate. SI plumose; remaining S setae simple. Labral lamellae consisting of 2 broad pectinate lobes. Chaetae branched; spinulae simple. Pecten epipharyngis consisting of 3 smooth scales. Chaetulae laterales simple to branched apically; chaetulae basales present. Ungula V-shaped, usually obscured by torma and anterior area of labrum in ventral view; basal sclerite elongate. Premandible broad, strong, and with faint indication of bifid apex; brush absent.
Mandible with apical tooth shorter than combined width of 2-3 inner teeth. Seta subdentalis short, straight, and apically blunt. Seta interna with plumose branches.
Mentum with 2 long median teeth and 4 pairs of much shorter lateral teeth present. Ventromental plate not visible. Seta submenti arising close to mentum.
Maxilla with palpiger with long simple or apically branched chaetulae. Galea without lamellae or pecten galearis. Setae maxillaris simple.
Body with parapods separate, each with an apical crown of claws. Procercus about as long as wide, bearing 6 anal setae. Anal tubules subglobular; dorsal pair lying on lateral surface of bases of posterior parapods. Lateral margin of abdominal segments, except last 2 segments, with row of setal tufts.
Xylotopus larvae mine in partly decomposed wood submerged in shallow, standing water or in the slower reaches of of flowing water.
One species is known from the Nearctic and another undescribed one from northern Burma.