Sensu Moller Pillot, 1984a
Body
Medium sized larvae up to 8 mm long. Living larvae yellow to pink. Claws on the posterior parapods are simpel. No lateral and ventral tubules (Wiederholm, 1983; Moller Pillot, 1984a).
Head
Length 0.40 - 0.55 mm with 3 pairs of eyes Pach arc eyes (Moller Pillot, 1984a)
Antenna
The antenna consists of 5 segments. The basal segment is longer than the flagellum.
Mentum
The mentum has 1 median tooth Parach arc mentum and 7 pairs of lateral teeth. The ventromental plates with striae radiating in all directions are 0.9 - 1.2 x as wide as the mentum.
Labrum
SI is simpel and labral lamellae are absent. The pecten epipharyngis is a plate with 7 distal teeth Parach arc pecten epiph. The premandible with 2 apical teeth.
Mandible
The mandible without a dorsal tooth, one long apical tooth and 2 brownish inner teeth. The pecten mandibularis is absent and seta subdentalis (SSD) is present (Wiederholm, 1983; Moller Pillot, 1984a).
Differential characteristics
The species with one median mental tooth can be distinguished by the flat mentum and 7 pairs of lateral teeth. Parach arc mentum. The species with 2 median teeth can be separated by the 7 pairs of lateral teeth, flat mentum Parach vitiosus mentum and 2-4 teeth on the premandible Parach vitiosus premandible where Harnischia has 6 teeth.
P. gr. arcuatus can be separated from the other Parachironomus by the single median mental tooth and striae on the ventromental plates radiating in all directions.