(Edwards, 1929)
Body
Medium sized larvae. The anterior and posterior parapods are separate and bear rows of claws. The body is covered with long setae (> 100 µm) (Wiederholm, 1983; Moller Pillot, 1984b; Saether, 1985).
Head
Head length 0.339 - 0.393 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 two median teeth with accesory teeth and 5 pairs of lateral teeth. The ventromental plates are large covering one or more mental teeth. The beard is well developed with numerous setae Rheocric fuscipes mentum.
Labrum
The pecten epipharyngis consists of three scales, SI is bifid and the premandible has one apical tooth (Wiederholm, 1983; Moller Pillot, 1984b; Saether, 1985).
Mandible
The mandible has an apical tooth and inner teeth (Wiederholm, 1983).
Differential characteristics
The bifid or serrate SI, large ventromental plates with beard Rheocricotopus mentum and procercus with spur separate Rheocricotopus from all other Orthocladiinae.
R. chalybeatus can be separated from the other Rheocricotopus by:
Median mental teeth with accesory teeth and long body setae.