(Freeman, 1959)
Body
Medium sized larvae up to 8.5 mm long. Living larvae red. Claws on the posterior parapods are simpel. No lateral and ventral tubules (Wiederholm, 1983; Moller Pillot, 1984a).
Head
Antenna
The antenna on a broad pedestal, consists of 5 segments. The second segment as long as the remaining segments and 2x as long as the 4th segment. The blade reaches to the base of the 5th segment. Lauterborn organs absent.
Mentum
The mentum has an indistinct crenate median tooth and 6 pairs of lateral teeth. The 4th pair is very small and the 5th lateral is larger than the neighbouring teeth Microch deribae mentum. The ventromental plates are 0.7-0.9x as wide as the mentum.
Labrum
SI is simpel and labral lamellae are absent. The pecten epipharyngis is either a simpel plate or distally divided into 3 lobes. The premandible has 2 apical teeth.
Mandible
The mandible without a dorsal tooth, apical tooth and 2 pointed inner teeth present Microch deribae mandible. The pecten mandibularis is absent and seta interna with 4 branches.
Differential characteristics
The flat mentum with the 5th lateral tooth larger than the neighbouring teeth Microch tener mentum is distinctive for the genus.
M. deribae differs from M. tener by the indistinct crenate median mentum tooth, the projecting inner mandibular teeth, the antennal blade shorter than the flagellum and the occurrence in brackish water only.