Small larvae, up to 3.3 mm long.
Antenna with 4 segments; segments 3 and 4 subequal in length, combined length subequal to segment 2. Ring organ in basal 1/2 of segment 1. Blade shorter than flagellum. Lauterborn organs as long as segment 3. Style undescribed.
SI bifid, SII short and stubby, SIII thin and weak, SIV a and b simple. Labral lamellae absent. Chaetae numerous, simple; spinulae simple. Pecten epipharyngis consisting of 5 scales (outer pair may be chaetulae laterales and part fused to next inner); Chaetulae laterales simple to serrate; chaetulae basales present. Ungula U-shaped. Premandible with 1 broad apical tooth; brush undescribed.
Apical tooth shorter than combined width of 3-4 inner teeth. Innermost tooth more appearing as swollen mola. Seta subdentalis lanceolate. Seta interna thin, with 6-7 branches, all simple. Mola smooth.
Mentum with 1 broad median and 4 pairs of lateral teeth. Ventromental plate broad and swollen, beard of several broad setae. Sclerotization of mentum not uniform with irregular longitudinal bands or dark sclerotization alternating with lighter bands thus appearing striated.
Body with separate anterior and posterior parapods, each bearing an apical crown of claws. Procercus well developed, but less than 1.5 times long as wide; 6-7 anal setae present; basal subapical seta undescribed. Anal tubules shorter than posterior parapods. Body setae apparently simple, shorter than 1/2 length of an abdominal segment.
Larvae of the only species, Kaniwhaniwhanus chapmani, are known from few streams in North Island of New Zealand, and tentatively from Lake Grasmere in South Island. In the Kaniwhaniwha stream larvae were present throughout the year, with exuvial evidence of greatest emergence in early spring and mid-summer.