Large larvae, 10-11 mm long. Body slightly to strongly reddish. Head capsule rounded-oval; cephalic index about 0.95. Dorsally, S5 anterior to S7, S8 variably posterodorsal to S7, DP aligned or unaligned with S7 and S8. Ventrally, VP more or less lateral of SSm, with S9 anterior to S10, both closer to VP than to SSm; thus SSm, S10 and VP may be aligned mediolaterally. All setae simple.
About as long as mandible. Antennal ratio about 6.3. Basal segment about 6x as long as apical width, with ring organ at c 0.85; segment 2 4x as long as wide-, segment 3 about 2x as long as wide, about equal in length to distal segment. Style extending beyond segment 3, situated with peg sensilla at side, below distal margin of segment 2. Blade shorter than flagellum. Accessory blade shorter than segment 2.
Slender, strikingly curved inwards in basal 1/3. Outer mandible smooth, without teeth. Apical tooth 2.5x as long as basal width, 1/5 length of mandible. Margin of mola with uniserial rank of saw-like teeth, increasing in size distally until largest tooth, subtending long seta subdentalis. Ventrolateral setae 1, 2 and ring organ clustered, seta 3 more basal, all setae simple.
Basal segment of palp about 2.5x as long as wide; ring organ at 0.6.
With fringe of swim-setae. Anal tubules conical. Procercus 4x as long as wide, with 18-20 apical setae. Some claws of posterior parapod with appressed points along inner side; smallest claws simple or broadened into oval shape basally.
Psectrotanypus differs from the closely related Derotanypus in the uniform shape of teeth on the ligula, the absence of spines or teeth on dorsal side of mandible, the straight mentum with weakly concave arrangement of dorsomental row of teeth, the outer ends of which are flattened posteriorly. In Derotanypus the row of teeth is strongly concave, the 2 or 3 outer teeth very close and partially fused at the base to form a compound tooth, which is dorsally curved and produced anteriorly.
Epler (2001) keys three species and provides ecological notes for species from s.e. USA.
Five species are described in Psectrotanypus: three from the Nearctic and two from the Palaearctic. Psectrotanypus lateralis Cheng & Wang and P. varius are reported from China. The genus is reported in the Neotropics from Costa Rica to Argentina, with a questioned record from Brazil. Larval Psectrotanypus are found in ponds, bogs, small bodies of water and slow-flowing streams, some species appear pollution tolerant, and in the Nearctic, P. dyari may live in elevated salinity in coastal rock pools.