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Chimaeriformes (class Chondrichthyes, subclass Holocephali) An order of marine fish that have a cartilaginous skeleton, a gill cover over the four gill openings, a naked skin, and no spiracle opening. The males have a pair of pelvic claspers and a peculiar clasping structure on the head. The order includes a number of fossil families as well as the living ghostfish. They are not considered to be closely related to either the sharks or the bony fish.