(Zetterstedt, 1838)
Body
Medium sized larvae with a length up to 8 mm. Living larvae are red-brown with yellow spots. The lateral side of the abdomen with a fringe of swimming hairs (Wiederholm, 1983; Moller Pillot, 1984a).
Head
The head length is 0.75 - 0.85 mm, about 1.5 times longer than wide with a cephalic index of 70-80% (Moller Pillot, 1984a).
Antenna
The antennal ratio is about 6.5. The ring organ is situated at 0.8 - 0.9 of the height of the first segment (Moller Pillot, 1984a).
Mentum
Dorsomentum with 4 - 5 teeth on each side Aps mentum.
Ligula and paraligula
Ligula with 5 brown teeth in a concave row. Paraligula with one large outer tooth and a much smaller inner tooth Aps ligula paraligula (Wiederholm, 1983; Moller Pillot, 1984a).
Mandible
The mandible has a large inner tooth.
Maxilla
The maxilla is short with one basal segment.
Anal tubules
4 anal tubules which are longer than wide.
Posterior parapods
No teeth on the inner margin of the claws.
Differential characteristics
Apsectrotanypus trifascipennis differs from the other genera in the tribe of the Macropelopiini by the small (4 - 5) number of teeth on the dorsomentum Aps mentum. With the length of 8 mm Apsectrotanypus larvae are smaller than the larvae of the related genera Anatopynia and Macropelopia.