Fries, 1830
Body
Medium sized larvae up to 8 mm long. Living larvae are grayish-green. The anterior and posterior parapods are separate and bear rows of claws. Procercus is appr. as high as wide and two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
The head length is 0.4 - 0.5 mm (Moller Pillot, 1984b).
Antenna
The antenna consists of six segments. The blade is shorter than the flagellum. Lauterborn organs are conspicuous (Wiederholm, 1983).
Mentum
The mentum has two median teeth that are as high as the first lateral teeth. Six pairs of lateral teeth are present Hydrob lugubris mentum. The ventromental plates are well developed. The beard is absent
Labrum
The pecten epipharyngis consists of three spines, SI is plumose Hydrob pilipes labrum and the premandible has two apical teeth and one inner tooth (Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth and 3 inner teeth. The seta interna has simpel branches (Wiederholm, 1983).
Differential characteristics
The combination of the antenna with 6 segments and the mentum with 6 pairs of lateral teeth are characteristic for Hydrobaenus Hydrob lugubris mentum, Trissocladius and Zalutschia. Trissocladius has a mentum with median teeth distinctly shorter than the first laterals Trissocl brevipalpis mentum and Zalutschia has a small beard Zalut gr. mucronata mentum.
H. lugubris can be separated from the other species by the mentum with median teeth not projecting over the first lateral teeth Hydrob lugubris mentum and procercus as high as wide.