Thienemann, 1921
Body
Medium sized larvae up to 7 mm long. Living larvae are pale-purple with light rings or purple-brown. The two posterior parapods bear rows of yellow claws. Procercus is strongly sclerotized, a little longer than wide, without apical spur Metr hirticollis agg procercus. Two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
Head is brown-yellow with head length up to 0.35 - 0.40 mm. 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 the antennal width. The blade is longer than the flagellum Metr hirtocollis agg antenna 8.
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 scirpi 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. martinii can be separated from the other species and Species-group of Metriocnemus by the first antennal segment being 2 x as long as the width Metr hirtocollis agg antenna 8 and the procercus well sclerotized but without apical spur. As only Metriocnemus species M. martinii lives in treeholes, filled with water.