Ammocryptocharax is a genus of tiny characins in family Crenuchidae, the South American darter characins, related to the better-known Characidium and Elachocharax. The atlas covers 4 species spread across Venezuela, Brazil, Colombia, Bolivia, Guyana, and Peru, in sandy-bottomed streams and blackwater creeks of the Amazon and Orinoco drainages. Adults stay tiny, from about 1–3.5 in, with an elongate, slightly compressed body and the cryptic, sand-toned patterning typical of the group - built to sit motionless on open sand rather than swim in open water.
These are specialist fish rather than trade staples: species such as the elegant sand darter (A. elegans) and the darter characin (A. lateralis) turn up only occasionally through importers who target small, sand-dwelling characins. In the aquarium they do best over a fine sand substrate with gentle current and leaf litter, picking at small live and frozen foods rather than competing at the surface. Conservation data are thin - three species are assessed Least Concern and one is Not Evaluated, reflecting how little targeted survey work has reached this small-bodied, easily overlooked genus.