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Class of vertebrate animals characterized by a cartilaginous endoskeleton, a skin covered by placoid scales, the structure of their fin rays, and the absence of a bony operculum (see gill cover), lungs, and swim-bladder. It includes the subclasses Elasmobranchii (sharks and rays) and Holocephali (ghostfish). The group extends back to the Late Devonian. It is not clear whether the cartilaginous skeleton is a primitive feature or the result of young fish reaching reproductive age prematurely, before a bony skeleton develops.

Subjects: Zoology and Animal Sciences.

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