Sensu Moller Pillot, 1984a
Species M. albolineatus and M. eurynotus p.p. (sensu Saether, 1995).
Ample evidence that these larvae hatch to both species. Larvae of M. hirticollis agg. however partly hatch to M. eurynotus sensu Saether, 1995 as well (pers. com. Moller Pillot).
Body
Medium sized larvae up to 8 mm long. Living larvae are purple with white bands. After preservation in ethanol the colouration remains. The two posterior parapods bear rows of brown claws. The procercus is higher than wide, sclerotized on the anal side and with an apical spur Metr hirticollis agg procercus. Two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
Head is dark brown with a pale spot around the eyes. Head length up to 0.35 mm. The eyes are fused, egg-shaped and it is difficult to distinguish the individuel 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 larger and projecting. Five pairs of lateral teeth present. The ventromental plates are weak and the beard is absent Metr hirticollis agg mentum.
Labrum
SI is strongly serrate and the labral lamella are serrate scales Metr hirticollis agg labrum. The premandible with 2 apical teeth.
Differential characteristics
The eye of Metriocnemus is distinctive. The smaller and larger eye are merged into eggschaped 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 pairs 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 Thienemannia Thienemannia gracilis anal seg by the well developed sclerotized procercus and the short seta on the procercus Metr scirpi anal segments.
M. hygropetricus agg. can be separated from the other taxa of Metriocnemus (except from M. hirticollis agg.) by the first antennal segment being 2 x as long as the width Metr hirtocollis agg antenna 8, the procercus well sclerotized and with an apical spur. C. hygropetricus agg. differs from M. hirticollis agg. by the purple body with white bands. M. hygropetricus agg. has a faint body colour.