The Anostomidae are a family of ray-finned fishes that belong to the order Characiformes. Closely related to the Chilodontidae and formerly included with them, the Anostomidae contain about 150 described species. Commonly known as anostomids, they are found in freshwater habitats from the Río Atrato in northernmost South America to warm-temperate central Argentina; they are of Amazon origin, with few found west of the Andes (mainly in Colombia and Venezuela). Their scientific name approximately means "mouth on top", from Ancient Greek áno- (ἄνω) "up" (as an adverb) + stóma (στόμᾶ) "mouth", in reference to the arrangement of these fishes' mouth opening. Description Anostomids have elongated bodies ranging from in length; their shape varies between fusiform and deeper-bodied, but even the latter are only moderately laterally. They have elongated, tapering heads with rather long, straight snouts, and small apical to upturned mouths immediately at or near the snout tip. This family contains many headstanders, which habitually swim with their heads pointing from 45° up to 90° downwards; most feed on plants near the bottom, while others also eat detritus and invertebrates picked up from river- or lakebeds. Adults guard the eggs after spawning. Anostomidae are generally considered edible, and some of the larger species are caught for food on a regular basis, much like large Leuciscinae (which are superficially similar Cypriniformes) are in the temperate Northern Hemisphere. Their jaws are rather short, with the maxillary bone small and excluded from the mouth opening, while the ascending process of the premaxilla is triangular in overall shape and robustly developed. One row of six or eight curved teeth occur in each jaw, arranged by length in a step-like fashion, with the front teeth being the longest; the pharyngeal teeth are enlarged and have two or more cusps each. Anostomid gill openings are small, with the gill membranes firmly joined to the isthmus; the ligament between the interopercle and the mouth is elongated and the interopercle is clearly separated from the retroarticular. On the sides of the preopercle is a large, elongated protrusion, where the powerful jaw adductor muscles attach. The third epibranchial gill arch has a curved anterior process which extends medially over the dorsal surface of the fourth infrapharyngobranchial arch. The circumorbital bone series is complete and includes a supraorbital bone, and at least four, often more, of the forward ribs are united by two or more intercostal ligaments. The lateral line