Cynodon is a genus of predatory characin in the dogtooth-tetra family Cynodontidae, close relatives of the much larger payara (Hydrolycus) and of Rhaphiodon. The atlas's 3 species (C. gibbus, C. meionactis, C. septenarius) reach 12–12.5 in and are distributed across the Amazon, Orinoco and Guiana Shield river systems, spanning Brazil, Guyana, Colombia, French Guiana, Peru, Suriname and Venezuela. Like their payara relatives, Cynodon are silvery, laterally compressed, fast-swimming fish armed with prominent fang-like teeth projecting from the lower jaw, built for ambushing smaller fish in open water.
These are specialist predatory fish rather than community-tank stock - their size, sharp dentition and requirement for a live or appropriately sized prey-fish diet keep Cynodon largely out of the general aquarium trade and mostly of interest to large-predator keepers or to ichthyologists studying South American piscivore diversity. Common names such as snub-nosed payara (C. gibbus) and adjeni (C. meionactis) reflect local rather than trade usage. All three species are currently assessed Least Concern, suggesting stable populations across their wide river-system range.