Small to medium-sized larvae, up to 6 mm long.
Antenna with 5 segments of variable lengths; segment 2 as long as the first; segment 4 subequal to, or much longer than third. Blade may extend beyond flagellum. Lauterborn organs usually longer than in Bryophaenocladius, about as long as antennal segment 3.
Labrum with SI and SII both simple and lanceolate; SIII more anterior than usual, inside SI setae. Scales of palatum simple, those of pecten epipharyngis small. Premandible with 3 teeth; brush absent.
Apical tooth shorter than combined width of 3 inner teeth. Seta interna and seta subdentalis (perhaps always) absent.
Mentum with 2 relatively broad median teeth and 4 pairs of lateral teeth. Ventromental plate distinct and sclerotized but apparently not extending beyond outer tooth of flattened mentum (despite figures to the contrary). No second pair of ventromental plates in specimens examined.
Maxilla with short palp. Lamellae on palpiger or galea absent. No setae on maxilla although sensillae, particularly sensilla basiconica well developed. No pecten galearis or appendix visible.
Body with anterior parapods present, fused, with fine setae but no claws. Posterior parapods present, each divided into 2 parts, anterior bearing claws, posterior without; posterior parapods capable of retraction into preanal segment. Parapods and anal segment at right angles to axis of body. Procercus absent but anal seta usually present. There may also be dorso-oral, anal, and preanal seta present.
Gymnometriocnemus s. str. larvae probably always are terrestrial in humus-rich soil, and pastures and cultivated fields and some crops, whereas those of the other subgenus G. (Raphidocladius) are aquatic, with G. (R.) acigus recorded from springs and a mountain stream in North America. European G. (R.) brumalis is recorded infrequently from aquatic habitats.