Strenzke, 1950
Body
Small larvae up to 5 mm long. Living larvae are stained with pale-purple or purple-brown. In ethanol the colouration is fainting but may still be visible. No coloured rings. The two posterior parapods bear rows of yellow to yellow-brown claws. Procercus is weakly sclerotized, without apical spur. Two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
Head length up to 0.3 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 1.5 x the antennal width. The blade is longer than the flagellum Metr inopinatus agg antenna.
Mentum
The mentum has a single median tooth. 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 inopinatus agg mentum.
Labrum
The pecten epipharyngis consists of three short scales, SI is serrate. Labral lamellae between the SI are serrate scales Metr inopinatus agg labrum.
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. inopinatus can be separated from the other species and Species-group[ of Metriocnemus by the first antennal segment being 1.5 x as long as the width Metr inopinatus agg antenna.