Medium-sized to large larvae, up to 17 mm long. Blood red larvae.
Frontal apotome, clypeus and labrum present, remaining labral area variably fragmentary. Clypeus equal width to frontal apotome.
Antenna with 5 segments, diminishing in size distally Lauterborn organs small, opposite on apex of 2nd segment, with short style. Ring organ in proximal 1/4 of segment 1, seta absent. Blade slightly shorter than flagellum, accessory blade 1/2 length of segment 2.
SI plumose along both sides, basomedially dilate; SII slender, coarsely plumose on each side; SIII short, slender; SIV normally developed. Seta praemandibularis simple. Labral lamellae normal, pectinate. Pecten epipharyngis tripartite, each plate with few strong distal teeth, and numerous small toothlets on surface. Premandible with 3 teeth, 2 inner teeth very broad, with beard.
Mandible without dorsal tooth; apical tooth slender, with 3 inner teeth, basal inner tooth with 2 humps. Pecten mandibularis modestly developed, lamellae simple. Seta subdentalis simple, slender. Seta interna inserted on dorsal surface, multi-branched. Mentum with all teeth dark brown/black. with 2 deeply sunken median teeth, 6 pairs of lateral teeth on each side, 1st broad and tall.
Mentum without delimited ventromentum and dorsomentum. Ventromental plates as wide as mentum, separated medially by 1/3 width of mentum, with coarsely toothed anterior margin. Setae submenti simple.
Lateral and ventral tubules absent.
The single species, H. quadripunctatum was previously placed in Tribelos and before that in Endochironomus (Reiss 1982b).
Hyporhygma larvae are easily identified by the deeply indented median teeth and tall first lateral tooth of the mentum. Even when the mentum is badly worn, which is often the case, the deep indentation is still apparent. Hyporhygma larvae are separable from the occasionally similar larvae of Endochironomus by the absence of clypeus and dorsal mandibular tooth and the presence of a 2-3 pointed basal inner tooth of the mandible, the SI which is feathered on both sides and by the fact that the anteromedian end of the ventromental plate is not produced.
Larvae of Hyporhygma mine in leaves and stems of Nymphaea species. One species is known from eastern North America, from Florida to Newfoundland.