Boschung, Herbert T. Formerly, Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama.
Last reviewed:July 2015
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An order of freshwater actinopterygian (ray-finned) fishes comprising the mooneyes and goldeyes. The order Hiodontiformes consists of one family, Hiodontidae; one genus, Hiodon; and two extant species, H. alosoides (goldeye) and H. tergisus (mooneye). Members were formerly placed in the order Osteoglossiformes, but they are now considered to be independent. Together, the two orders (Hiodontiformes and Osteoglossiformes) comprise the extant Osteoglossomorpha, a primitive group of teleost fishes. Hiodontids superficially resemble clupeids and, for many years, were classified as clupeiforms. The body is deep and laterally compressed and has a ventral keel, but the keel is not serrated as in most clupeids; the eyes are far forward and large, with the diameter greater than the length of the snout; the scales are large and cycloid, and either bright silvery or golden; the anal fin base is much longer than the dorsal fin base; and the caudal fin is forked (see illustration). The goldeye differs from the mooneye in having 9 or 10 principal dorsal fin rays, versus 11 or 12; and a ventral keel extending anteriorly past the pelvic fins, versus not extending anteriorly past the pelvic fins. See also: Actinopterygii; Clupeiformes; Osteichthyes; Osteoglossiformes; Teleostei
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