Small larvae, up to 5 mm long. Body yellow; head capsule pale yellow to yellowish brown.
Antenna with 5 segments; segments consecutively smaller; segment 5 hair-like and vestigial. Antennal ratio 1.0-2.3. Ring organ in basal 1/4 of segment 1. Blade shorter than flagellum. Lauterborn organ usually distinct, as long as third segment.
Labrum with SI-SIII weak and simple. Spinulae and chaetae reduced or absent. Pecten epipharyngis consisting of 3 equal, simple, sharply pointed spines. Only 1 pair of chaetulae basales present; 6-7 pairs of chaetulae laterales present, all simple. Premandible with simple or faintly developed apical tooth or with 3-5 apical teeth.
Apical tooth much longer than combined width of 3 inner teeth. Seta subdentalis long and pointed. Seta interna with 3-5 branches.
Mentum with median tooth broad to extremely broad, partially double. 3, 5, or 6 pairs of lateral teeth; normally 6 pairs, but first and second teeth sometimes fused; or first, second, and third lateral teeth fused with median tooth; lateral teeth occasionally very indistinct and minute. Ventromental plate large to extremely long, with a rounded or a straight caudolateral apex; beard absent but in one species of (N. Plecopteracoluthus Steffan) with a brush of setae on small plates, one to each side of mentum; sometimes with irregular striae either on plates or on cardo (cardinal striae).
Maxilla with most chaetae and lamellae reduced in numbers or shortened. Pecten galearis absent or very faintly indicated.
Body with well developed parapods; anterior claws smooth or weakly to strongly serrated. Procercus well developed, sclerotized caudally, probably always with 2-3 small spines or tubercules; with 3-6 anal setae. Supraanal seta inconspicuous or absent. 4 anal tubules, either all of about equal length and shorter than posterior parapods or 1 pair longer than posterior parapods.
The subgenus Plecopteracoluthus Steffan (which may not be monophyletic) includes several lotic species that are phoretic, or more likely, parasitic, on other aquatic invertebrates, including Plecoptera, Megaloptera and Hemiptera. Species of the nominate subgenus are lentic and lotic, often associated with filamentous algae.