Chondrichthyes
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Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Image: Myliobatis aquila sasrája
Image: Sphyrna mokarran at georgia
Image: Hornhai (Heterodontus francisci)
Fish fin
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Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported only by muscles.
Dorsal fin of a chub (Squalius cephalus)
Skeleton of a lingcod, a ray-finned fish
Lobe-finned fishes, like this coelacanth, have fins that are borne on a fleshy, lobe-like, scaly stalk extending from the body. Due to the high number of fins it possesses, the coelacanth has high maneuverability and can orient its body in almost any direction in the water.
Pectoral fin with fleshy lobe of Latimeria chalumnae (Citron / CC-BY-SA-3.0)