Family Chilodontidae 114headstanders Freshwater northern South America

Premaxilla relatively small, maxilla much enlarged; uppermost of three post-cleithra typical of the order missing; 7-10 branched dorsal fin rays; lateral line scales about 25-31; sixth lateral-line scale smaller than the other scales; highly modified pharyngeal apparatus; single series of relatively small teeth movably attached to jaws. Maximum length 18 cm.

Two genera, Caenotropus (3) and Chilodus (4), with seven species (Vari and Raredon, 2003).

Superfamily Crenuchoidea

Family CRENUCHIDAE (115)—South American darters. Freshwater; eastern Panama and South America.

Paired foramina in the frontal bones, posterodorsally to the orbits (pronounced in Crenuchinae but very small in the Characidiinae). Crenunchids are relatively small, usually under 10 cm SL.

Both subfamilies were recognized a subfamilies of a large Characidae in Nelson (1994); they are placed here as a monophyletic group in the family Crenuchidae following Buckup (1998, 2003). Twelve genera and 74 species.

Subfamily Crenuchinae. Enlarged lateral frontal foramina (Buckup, 1998, lists an additional synapomorphic features supporting monophyly for this taxon). Poecilocharax lacks an adipose fin. Maximum length only 5.7 cm TL. Northern South America.

Two genera, Crenuchus (1) and Poecilocharax (2), with three species.

Subfamily Characidiinae. Anal fin with fewer than 14 rays. Buckup (1993a), lists some 13 synapomorphic features supporting monophyly for this taxon and provides a diagnosis for the then known genera and species. Eastern Panama and South America south to northern Argentina and uruguay). Some species of Characidium have the remarkable ability to climb waterfalls by using their paired fins to cling to the underside of rocks (Buckup et al., 2000). As noted by these authors, some species of Awaous and reportedly of Trichomycteridae, Astroblepidae, Rivulidae, and Balitoridae are able to surmount waterfalls (adult Entosphenus and juvenile Galaxias apparently can also surmount falls and/or dams).

Ten genera, Ammocryptocharax (4), Characidium (47), Elachocharax (4), Geryichthys (1), Klausewitzia (1), Leptocharacidium (1), Melanocharacidium (8), Microcharacidium (2 plus 1 incertae sedis), Odontocharacidium (1, recognized as Klausewitzia aphanes in Nelson, 1994), and Skiotocharax (1), with about 71 species (Buckup, 1993b, 2003).

Superfamily Hemiodontoidea

Family HEMIODONTIDAE (116)—hemiodontids. Freshwater, usually pelagic; northern South America, south to the Paraná-Paraguay Basin.

Body subcylindrical to fusiform (and fast swimming fishes); adipose eyelid well developed; teeth absent on lower jaw in adults; gill membranes free; adipose eyelid present; lateral line scales 50-125; pectoral fin rays 18-23; 9-11 branched pelvic rays; most species with round spot on side of mid-body and stripe along lower lobe of caudal fin; vertebrae 40-45. Langeani (1998) lists synapomorphies for the family and its lower taxa. Maximum length about 30 cm SL.

Five genera with about 28 species, with several undescribed species (Langeani, 2003).

Subfamily Anodontinae. Anodus has jaw teeth absent; numerous elongate gill rakers, up to 200 on first arch (more than any other characoid) depending on fish size; pharyngeal structures specialized for filter feeding on plankton, while Micromischodus sugillatus is the only hemiodontid with teeth on lower jaw throughout life.

Two genera, Anodus (2, synonym Eigenmannina) and Micromischodus (1), with three species (Langeani, 2003).

Subfamily Hemiodontinae tribe hemiodontini. One genus, Hemiodus (synonyms Hemiodopsis and Pterohemiodus), with about 18 species (Langeani, 2003).

tribe bivibranchiini. The only characiform with a highly protrusible upper jaw with a unique mechanism of protrusion (especially pronounced in Bivibranchia); premaxilla minute and firmly attached to anterior end of maxilla. Bivibranchia also has a number of other derived modifications, including a unique elaboration of the glossopharyngeal and vagus nerves.

Two genera, Argonectes (2) and Bivibranchia (synonym Atomaster, 5), with about seven species (Langeani, 2003).

Superfamily Alestioidea

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