Edwards, 1929
Body
Preserved larvae are light-purple without white bands. The two posterior parapods bear rows of yellow claws. Procercus is sclerotized, as long as wide, without apical spur. Two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
Head is brown. The eyes are fused, egg-shaped and difficult to distinguish the individual eyes Metr hirtic agg head lateral.
Antenna
The antenna consists of five segments. The first segment is 2 x as long as the antennal width. The blade is longer than the flagellum.
Mentum
The mentum has 2 median teeth. The first lateral teeth are large and projecting. Five pairs of lateral teeth present. The ventromental plates are weak and the beard is absent Metr hirticollis agg mentum.
Differential characteristics
The eye of Metriocnemus is distinctive. The smaller and larger eye are merged into one egg-shaped eye Metr hirtic agg head lateral. In all other genera the smaller eye can be distinguished from the larger eye Limnophyes head lateral. Metriocnemus can be separated from all genera except Thienemannia by the mentum with 5 pair of lateral teeth and the weak ventromental plates Metr hirticollis agg mentum, antenna 5 segmented Metr hirtocollis agg antenna 8, plumose SI and labral lamellae Metr hirticollis agg labrum, mandible with 4-5 teeth Metr terrester mandible. Metriocnemus can be separated from Thiemannia Thienemannia gracilis anal seg by the well developed sclerotized procercus and the short seta on the procercus Metr scirpi anal segments.
M. tristellus is the only Metriocnemus with the first antennal segment = 2 x the width of the segment. In albofasciatus-agg and corticalis agg the ratio = 2.4. Also the procercus is as wide as high without an apical spur (versus higher than wide and with an apical spur).