Chilodus is a genus of headstanders in family Chilodontidae, part of the wider Characiformes order that also holds the tetras. The atlas's 4 species range 2.5–3 in and are distributed across the Amazon, Orinoco, and Guiana Shield river systems, with records in Brazil, Colombia, Peru, Suriname, Ecuador, French Guiana, and Guyana. The genus takes its common name from a distinctive swimming posture: individuals hold themselves at a steep, head-down angle rather than swimming level, a habit tied to how they feed — grazing biofilm, algae, and fine organic material off submerged wood, leaf litter, and plant surfaces rather than taking food from open water.
The spotted headstander (Chilodus punctatus) is the species most familiar to the aquarium hobby, kept in peaceful planted community tanks partly for its odd head-down posture and partly for its grazing habit, which can help keep biofilm and soft algae in check on decor and leaf surfaces — though it isn't a dedicated algae-eater. The petite headstander (C. gracilis) appears occasionally in the trade as a smaller alternative; C. fritillus and C. zunevei are little known outside of ichthyological collections. Three of the four atlas species carry a Least Concern rating; one has not yet been formally assessed.