Kieffer in Thienemann and Kieffer, 1916
Body
Medium sized to large larvae 9-15 mm long. Living larvae red. No lateral and ventral tubules. (Wiederholm, 1983; Moller Pillot, 1984a).
Head
The dorsal part of the headcapsule is coarsely granulated and therefore dull. Anterior margin of the frontoclypeal apotome is straight. Labral sclerite 1 is divided in 2 plates and sclerite 2 is set forward so in all 3 labral sclerites are present Xeno labral sclerites 8.
Antenna
The antenna consists of 5 segments. The blade only reaches to the tip of the third segment. Lauterborn organs distally on the second segment.
Mentum
The mentum is strongly bend laterally which makes it hard to distinguish the separate teeth Xenochir mentum especially since the mentum usually is heavily worn Xeochir worn mentum. The middle tooth is dome shaped with two small first lateral teeth, all middle teeth lower than the second lateral tooth. The third lateral tooth lower than its neighbouring teeth and the outer teeth diminishing in size laterally. The ventromental plates are about 1,2x as wide as the mentum.
Labrum
Labrum with 2 lobes heavely beset with long chaetae, showing a "moustache" in lateral view under low magnification Xenochir head lateral 8. SI is simpel and labral lamellae 2 thin spines. The pecten epipharyngis with 3 slender scales and apical toothlets. The premandible is strongly reduced.
Mandible
The mandible without a dorsal tooth, apical tooth very strong with 3 very small inner teeth, The pecten mandibularis is present and seta interna with 4 plumose branches.
Differential characteristics
Xenochironomus is an abbarant genus with a labral "moustache" Xenochir head lateral 8, strongly bent mentum, no dorsal mandibular tooth, very small inner teeth, granulated dorsal head capsule and 3 labral sclerites Xeno labral sclerites 8. Xenochironomus is, with Demeijerea, the only genus living in freshwater sponges.