Kieffer, 1921
Subgenus Euorthocladius Thienemann, 1935
Body
Small larvae up to 4.5 mm long. The L4 setae are simpel, appr. 200 µm long. The anterior and posterior parapods are separate and bear rows of claws. Procercus and two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
Headcapsule pale to brown-yellow with a distinct pale stripe across the posterio-dorsal part of the head. Head length 0.297 - 0.363 mm (Schmid, 1993).
Antenna
The antenna consists of five segments. The blade is shorter than the flagellum. Lauterborn organs are distinct.
Mentum
The mentum has one median tooth and 6 pairs of lateral teeth. The mentum ratio is 0.9 - 1.55 (Schmid, 1993). The ventromental plates are weak. The beard is absent (Wiederholm, 1984a).
Labrum
The pecten epipharyngis consists of three scales, SI is bifid and premandible with one apical tooth Orth frigidus labrum9 (Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth of normal length and 3 inner teeth Orth frigidus mandible. The seta interna is present (Moller Pillot, 1984b).
Differential characteristics
Orthocladius can be separated from all other genera, except Paratrichocladius, by the bifid SI, mentum with 1 median tooth and 6-9 pairs of lateral teeth, 5 segmented antenna (4 in O. consobrinus) and simpel body seta. Paratrichocladius however has a blueish thorax in freshly preserved larvae and a lobed ring beneath the ssd of the mandible. Both characters are absent in Orthocladius.
Orthocladius luteipes can be separated from the other Orthocladius with a pale to light brown head by:
L4 appr. 200 µm, head length 0.297 - 0.363 mm, mentum ratio 0.9 - 1.55 and a pale stripe across the postero-dorsal head capsule (Schmid, 1993).