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a subclass of chondrostean fishes closely related to Selachoidei. The body length reaches 1.2 m. The skeleton is cartilaginous. The skull is autostylic, that is, the palatoquadrate cartilage is completely merged with the skull. The four gill clefts are covered by a cutaneous fold, owing to which there is only one pair of external gill openings. The teeth are cutting or grinding. The ventral fins of males are converted into copulatory organs. There is no cloaca. Fossils are known from the Upper Devonian. There are two orders: the extinct Chondrenchelyiformes (marine fishes that lived in the Carboniferous and had pectoral fins with a central segmented axis) and the extant Chimaeriformes.