Large larvae, up to 16 mm long.
Antenna with ring organ in basal 1/2 to basal 1/3 of basal segment. Blade slightly longer than flagellum.
Labrum with SI with apical teeth; other S setae normal. Labral lamellae broad, pectinate. Chaetae serrated, chaeta media conspicuous. About 4 spinulae present. Pecten epipharyngis consisting of 3 scale-like spines. Chaetulae laterales smooth; chaetulae basales well developed, simple. Premandible with 1 apical and 1 inner accessory tooth; brush absent.
Mandible with long, single apical tooth and 2 inner teeth. Seta interna with 5 setae serrated on basal side and 2 longer smooth setae.
Mentum with 13 teeth; median tooth broad, concave. Ventromental plate elongate, relatively narrow; with about 4-9 weak setae in beard.
Maxilla with lacinial chaetae short. Anterior lacinial chaeta large, oval. Lamellae of galea scale-like, triangular, smooth. Apparently no cardinal beard present.
Body without conspicuous body setae.
Larvae of Monodiamesa are found in littoral to profundal zones of mesotrophic to strongly oligotrophic lakes, most commonly on sandy substrates. Also sporadically in flowing water and eutrophicated lakes. Holarctic and Neotropical in distribution. Seven species from Holarctic region, six known as larvae.