(Zetterstedt, 1850)
Body
Large larvae up to 18 mm long. Living larvae red. No lateral and ventral tubules. (Wiederholm, 1983).
Head
The head is shining. Anterior margin of frontoclypeal apotome is convex without a subapical pit. Labral sclerites 1 absent and sclerite 2 is present.
Antenna
The antenna consists of 5 segments. The blade is as long or a little shorter than the flagellum. Lauterborn organs distally on the second segment.
Mentum
The mentum has 4 median brown teeth and 6 pairs of brown lateral teeth. The median teeth are set forward and are connected to the ventromental plates that are as wide as the mentum Serg mentum.
Labrum
SI is plumose on both sides and labral lamellae a single plate with numerous distal teeth. The pecten epipharyngis consist of 3 plates with distal teeth. The premandible has 2-4 teeth.
Mandible
The mandible with a short dorsal tooth, apical tooth and 4 inner teeth all brown Serg mandible 8. The pecten mandibularis is present and seta interna with 4 plumose branches
Differential characteristics
Sergentia can be separated from all other genera by the 4 median mental teeth Serg mentum and 4 inner mandibular teeth Serg mandible 8, combined with the presence of labral sclerite 2. Phaenopsectra Phaenops mentum and Tribelos Trib mentum have a similar mentum. Phaenopsectra has shining black mental teeth, a mandible with only 3 inner teeth and the headcapsule is finely granulated and therefore dull. Tribelos has also labral sclerite 1 present, only 2 middle teeth on the mentum are connected to the ventromental plates and the mandible has only 3 inner teeth.