answers: Elasmobranchii
context: Chondrichthyes Chondrichthyes (; from Greek χονδρ- "chondr-" 'cartilage', ἰχθύς "ichthys" 'fish') is a class that contains the cartilaginous fishes: they are jawed vertebrates with paired fins, paired nares, scales, a heart with its chambers in series, and skeletons made of cartilage rather than bone. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class). Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates. The skeleton is cartilaginous. The notochord is gradually replaced by a vertebral column during development, </s> in the water. They have been seen doing headstands and swimming belly up. It is thought that their rostral organ helps give the coelacanth electroperception, which aids in their movement around obstacles. Ray-finned fishes are a class of bony fishes called Actinopterygii. Their fins contain spines or rays. A fin may contain only spiny rays, only soft rays, or a combination of both. If both are present, the spiny rays are always anterior. Spines are generally stiff and sharp. Rays are generally soft, flexible, segmented, and may be branched. This segmentation of rays is the main difference that separates them </s> Chaenopsidae The blennioid family Chaenopsidae includes the pike-blennies, tube-blennies, and flagblennies, all perciform marine fish. The family is strictly tropical, ranging from North to South America. Members are also present in waters off Japan, Taiwan and Korea. Fourteen genera and 90 species are represented, the largest being the sarcastic fringehead, "Neoclinus blanchardi", at in length; most are much smaller, and the group includes perhaps the smallest of all vertebrates, "Acanthemblemaria paula", measuring just long as an adult. With highly compressed bodies, some may be so elongated as to appear eel-like; chaenopsids are scaleless and lack lateral lines. Their heads are
question: sharks rays and skates belong to what group