Boschung, Herbert T. Formerly, Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama.
Last reviewed:July 2015
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An order of galeomorph sharks that are commonly known as the bullhead sharks. Sharks belonging to the order Heterodontiformes are distinguished by the following combination of characters: a typically sharklike (subcylindrical) trunk; a head that is elevated above the eyes, but with a blunt and flattened snout; a small mouth; teeth that are similar in both jaws; spiracles present; eyes that lack a nictitating fold or membrane (which is at the inner angle of the eye or below the eyelid and is capable of extending over the eyeball); two dorsal fins, each with a well-developed spine; anal fin present; oviparous development; and an egg case that is horny with spiral flanges, but no tendrils. They comprise one family (Heterodontidae), one genus (Heterodontus), and nine species, which vary in maximum total length from 57 to 165 cm (22 to 65 in.) [see illustration]. See also: Elasmobranchii; Selachii
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