The only extant order of the chondrichthyan subclass Holocephali, and the closest living relatives of the Elasmobranchii (sharks and rays). The chimaeriformes (ratfishes) are a distinctive group of marine fishes that mostly inhabit the deeper parts of the world's oceans, especially in the Atlantic and Pacific. Some species move to coastal waters during the winter months, and a few species may be restricted to these environments. Modern ratfishes are divided into three families, distinguished by the shape of the snout: Chimaeridae, Rhinochimaeridae, and Callorhinchidae.