Medium-sized larvae, up to 7 mm long.
Antenna with ring organ in basal 1/3 of basal segment. Blade slightly shorter than flagellum.
Labrum with SI unique, biarticulate with apical part laterally fringed; SIV A triarticulate; other S setae normal. Labral lamellae made up of 2 setal tufts. Chaetae twisted, with lateral fringe in apical half. Spinulae reduced. Pecten epipharyngis consisting of brushes of thin, hair-like setae. Chaetulae laterales thin and fringed; chaetulae basales minute, with broad base and thin point. Premandible with 2 slender, apical teeth, 2 inner notches and well developed brush.
Mandible with apical tooth longer than combined width of 3 indistinct inner teeth. Pecten mandibularis brush-like. Seta subdentalis long and thin. Seta interna with 30-40 smooth branches. Lateral setae brush-like.
Mentum with 15 teeth; median tooth broad, convex and pale. Ventromental plate broad and long; strong setae in beard.
Maxilla with anterior lacinial chaeta apparently with broad to truncate apex. Lamellae of galea hair-like, numerous.
Body without conspicuous body setae.
Larvae of only well described species, O. fulva, lives in sandy, lightly silted sediments of slow flowing waters including the littoral zone of lakes. Larvae feed on algae using a passive filtration method. Holarctic. Taxonomy needs revision.