Rhytiodus is a genus of headstanders, family Anostomidae, from South American river systems - the atlas records it from Brazil, Bolivia, Colombia, Peru, and Ecuador, broadly the Amazon and adjoining basins. Like other anostomids, Rhytiodus has an elongate, torpedo-shaped body and the family's signature head-down, tail-up foraging posture, used to graze algae, biofilm, and plant matter from submerged wood and rock. Atlas species run 6–13 in, a solidly mid-to-large size within the characiform world and noticeably bigger than the small tetras many aquarists associate with the order.
Rhytiodus turns up only occasionally in the aquarium trade, mostly among keepers of large planted or biotope tanks looking for an algae-grazing characin with genuine presence; it is far less commonly offered than its better-known anostomid relative Anostomus. Two species in the atlas carry the common name silver headstander (A. argenteofuscus and A. microlepis), reflecting a shared, plain silvery coloration typical of the genus. Conservation status is unremarkable by the numbers available - three Least Concern species and one Data Deficient - with no strong signal of range-wide pressure.