(Schrank, 1803)
Body
Small larvae. Living larvae red. No lateral and ventral tubules (Wiederholm, 1983; Moller Pillot, 1984a).
Head
The head capsule is shining. 266 - 281 µm long. The eyes are small well separated Pol scal eyes pict9. The gula is pale. Anterior margin of frontal apotome is straight without a subapical pit, but with anterio-lateral lobes on which the S3 is inserted. Labral sclerite 1 absent, sclerite 2 present.
Antenna
The antenna consists of 4 (5?) segments. Segments 3-4 (5?) are strongly reduced. The final segment might be a lauterborn organ Pol scal antenna9. The antennal blade reaches far beyond the apex of the flagellum.
Mentum
The mentum has 2 median teeth and 7 pairs of lateral teeth. The first lateral teeth are reduced Pol g nub mentum 8.
Labrum
SI is plumose on both sides and labral lamellae a single plate with numerous distal teeth. The pecten epipharyngis with 3 small plates with distal teeth Pol pecten epiph. The premandible has three teeth.
Mandible
The mandible with a dorsal tooth, one apical tooth and 2 inner teeth Pol g nub mandible. The pecten mandibularis is present and seta interna with plumose branches.
Differential characteristics
Two median and 7 pairs of lateral teeth on the mentum Pol g nub mentum 8, with Lauterborn organs on the second segment and shining dorsal headcapsule will separate Polypedilum from all other genera except from Parachironomus which however has a completely different mentum Parach arc mentum.
P. scalaenum can be separated from the other Polypedilum by the small head (length < 300 µm). Also the aberrant flagellum of the antenna is distinctive.