Anostomus is the type genus of family Anostomidae, the headstanders - characiform fish named for their distinctive oblique swimming posture, cruising with the head angled downward. The atlas's five species come from Brazil, Peru, Suriname, Colombia, French Guiana, Guyana, and Venezuela, spanning Amazon, Orinoco, and Guiana Shield drainages. They share an elongated, torpedo-shaped body and a small, upturned mouth adapted for grazing algae and biofilm off submerged wood and rock, typically in clear or blackwater streams with moderate current. Atlas sizes run 4–8 in.
Anostomus anostomus, the striped headstander, is a long-standing aquarium trade fixture, prized for its bold black-and-gold longitudinal stripes and peaceful, algae-grazing habits in large, driftwood-furnished tanks; Anostomus ternetzi (Ternetz's headstander) shows up in the trade under similar care. The remaining species - A. brevior, A. longus, and A. ucayalensis - are seen far less often and are mostly of taxonomic interest. Conservation leans reassuring: three of five species rate Least Concern, with only one Data Deficient and one Not Evaluated, suggesting no acute threat even where formal assessment is thin.