Kieffer, 1909
Subgenus Euorthocladius Thienemann, 1935
Body
Small to medium sized larvae up to 5.5 mm long. The L4 setae are simpel, appr. 200. 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 without a pale stripe across the posterio-dorsal part of the head. Head length 0.489 - 0.510 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 8 - 9 pairs of lateral teeth. The mentum ratio is 3.85 - 4.25 (Schmid, 1993). The ventromental plates are weak Euorth rivulo mentum. 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 long apical tooth and 4 inner teeth. The seta interna is present (Moller Pillot, 1984b; Schmid, 1993).
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.
The mentum with 8 - 9 pairs of lateral teeth is distinctive among Orthocladius Euorth rivulo mentum (Schmid, 1993).