Spaerck, 1923
Body
Medium sized to large larvae up to 9.1 mm long. Living larvae are white. The anterior parapods are separate. The two posterior parapods bear rows of claws. Procercus and two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
The head length is 0.35-0.47 mm in H. marcidus which has a distinct dark marking beneath the mentum Heterotr marcidus head ventr (Moller Pillot, 1984b).
Antenna
The antenna consists of seven segments Heterotr marcidus antenna. Segment 3 much shorter than segment 4. The blade is longer than the flagellum in the subpilosus groep and shorter in the maeaeri and marcidus groups (Saether, 1975). Lauterborn organs are reduced or absent (Wiederholm, 1983; Moller Pillot, 1984b)
Mentum
The mentum has one or two median teeth and 5 pairs of lateral teeth. The ventromental plates are large. The beard is absent Heterotr marcidus mentum.
Labrum
The pecten epipharyngis consists of three serrated spines, SI is plumose and the premandible has two indistinct teeth (Wiederholm, 1983).
Mandible
The mandible has an apical tooth and 3-4 inner teeth. The seta interna has branches (Wiederholm, 1983).
Differential characteristics
The antenna with seven segments Heterotr marcidus antenna is distinctive for Heterotrissocladius and Paratrissocladius. Paratrissocladius however has a mentum with only 4 pairs of lateral teeth and the ventromental plates are weak Paratrissocl exc mentum.
Diversity
European species: 5
Treated species:
Heterotrissocladius grimshawi
Heterotrissocladius maeaeri
Heterotrissocladius marcidus
Heterotrissocladius subpilosus