(Edwards, 1929)
Subgenus Allopsectrocladius
Body
The purple tracheal stems are distinct. The anterior and posterior parapods are separate and bear rows of claws. Procercus brown sclerotized with 2 large spurs Psec platypus procercus9 and two pairs of anal tubules present. The claws on the posterior parapods are brown (Wiederholm, 1983; Moller Pillot, 1984b).
Head
The head length is 0.5-0.6 mm (Moller Pillot, 1984b).
Antenna
The antenna consists of five segments. The blade is shorter than the flagellum. Lauterborn organs are small or absent.
Mentum
The mentum is flattened with a small median incision Psec platypus mentum. The ventromental plates are large covering some lateral teeth. The beard is distinct.
Labrum
The pecten epipharyngis consists of three subequal spined scales, SI is palmate Psec barbimanus S1 and the premandible has one apical tooth (Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth which is about 2.5 x the length of the combined inner teeth. The tip is black and the basal part of the apical tooth is pale Psec platypus mandible9. The seta interna is absent (Wiederholm, 1983; Moller Pillot, 1984b).
Differential characteristics
The combination the palmate SI Psec barbimanus S1 on the labrum, beard present and procercus with spurs Psec psilopterus procercus9 is distinctive for the genus Psectrocladius.
P. platypus can be separated from all other Psectrocladius by the distinct tracheal stems and the head length 0.6 mm.