(Walker, 1856)
Body
Medium sized larvae up to 6.6 mm long. The two posterior parapods are separate. Procercus with a subapical spur and two pairs of anal tubules present (Saether 1976).
Head
The head length is 0.36-0.4 mm (Saether, 1976).
Antenna
The antenna consists of seven segments. Segment 3 is much smaller than segment 4. The blade is subequal to the flagellum. Lauterborn organs probably absent.
Mentum
The mentum has two large median teeth and 4 pairs of lateral teeth. The ventromental plates are moderately developed. The beard is absent or consists of 1-2 hairs Paratrissocl exc mentum (Saether, 1976).
Labrum
The pecten epipharyngis consists of three scales, SI is split distally, leaving two short plumose branches. The labral lamellae are simpel and the premandible has one apical tooth and one inner tooth (Saether, 1976).
Mandible
The mandible has an apical tooth and 3 inner teeth. The seta interna has smooth and serrated branches (Wiederholm, 1983).
Differential characteristics
Paratrissocladius is characterized by a mentum with four pairs of lateral teeth Paratrissocl exc mentum and a spur on the procercus. With Heterotrissocladius it shares the same 7 segmented antenna, but Heterotrissocladius has a mentum with 5 pairs of lateral teeth Heterotr marcidus mentum.