Small larvae, up to 3 mm long. Head yellowish brown; body pale, brownish. Head capsule slender; cephalic index about 0.45. Cephalic setae and sensilla distinctive: dorsally S8 displaced far posterior and lateral to S7, S5 is more mesal on apotome, near aligned to S7 and faint DP. Ventrally VP large and oval, posterior to but close to S10 which lies posteromedial to S9; SSm positioned far posterolaterally to VP. S5 short, simple, S7 short, few-branched, S8 long, simple, S9 long, simple, S10 short, simple, SSm short, multi-branched.
Relatively long, 3/5 length of head, 4.5x as long as mandible. Antennal ratio 2.3-3.2. Basal segment about 7.5x as long as basal width, with ring organ at 0.7; segment 2 8x as long as wide; segment 3 long, 5.5x as long as wide, 2x as long as last segment. Style cylindrical in basal 1/2, apical part thickened; extending beyond middle of segment 4. Peg sensilla 1/2 as long as segment 3. Blade as long as flagellum; basal ring 3x as high as wide. Accessory blade as long as blade or somewhat shorter.
Weakly curved, apical 1/2 narrowed. Apical tooth 2.5x as long as greatest width, about 1/4 length of mandible. Inner tooth large, pointed; small accessory tooth at base of apical tooth; mola extended tooth-like with apically-produced point; seta subdentalis large. Ventrolateral setae and ring organ aligned, close together on proximal 1/2 of mandible; seta 3 simple.
Basal segment of palp about 2.5x as long as wide; ring organ large, at 0.15-0.2.
Without fringe of swim-setae. Anal tubules long and slender, at least as long as posterior parapods; slight constriction present shortly before distal 1/3. Preanal setae even longer than anal tubules. Procercus dark, about 3X as long as wide, with 7 apical setae. Claws of posterior parapod yellowish-brown; larger claws with fine spinules on inner and/or outer margin; sometimes 1-2 medium-sized claws with coarse spines or 1 claw with complete inner comb of spines; claws of anterior parapod partly with combs.
Nilotanypus is a Pentaneurini; species of this genus are among the smallest Tanypodinae. The ventral cephalic setal pattern is unique, with SSm retracted to the posterior half of the head, and S8 also very retracted. Otherwise the long anal tubules and large preanal setae resemble those of Labrundinia and Pentaneura. In common with Labrundinia the middle tooth of the ligula is elongate and the ligula has an approximately triangular granulose basal area, but Nilotanypus has a smooth head and the molar expansion ('tooth') is much larger in Labrundinia than in Nilotanypus. At least one small or medium claw of the posterior parapod of Nilotanypus is pectinate or with several small spines.
Epler (2001) extends and complements Roback's (1986) keys to larvae of Nearctic species.
Larvae of Nilotanypus inhabit flowing waters, especially with sandy beds: here, they may be the dominant tanypodines.
N. dubius is widespread in Europe from northern latitudes to Algeria, and eastward to Japan; N. minutus is a second Japanese species. Four species are known from North America: N. americanus, N. fimbriatus, N. kansensis and an unnamed species from Texas (Roback, 1986). Evidence from pupal exuviae suggests a Neotropical distribution from Costa Rica to Brazil, but no species have been described (Spies and Reiss, 1996). Nilotanypus is present in the Oriental region with two species N. polycanthus and N. quadratus described from China (Cheng and Wang, 2000). Larval Nilotanypus are abundant in sandy-bedded streams of s.e. Asia (Cranston 2004) and Australia where an abundant species may be identical to that found by Zavrel in Sumatra (Indonesia) (Cranston 2000).