Living fish fall into three main groups: jawless fish, cartilaginous fish, and bony fish. Jawless fish are the hagfish and lampreys, a small group of a little over 100 species that lack true jaws. Cartilaginous fish, with more than 1,100 species, have skeletons made of cartilage rather than bone and include sharks, rays, and chimaeras.
Bony fish are by far the largest group, with more than 32,000 described species. They are divided into ray-finned fish, which include nearly all familiar fish such as salmon, tuna, and goldfish, and lobe-finned fish, a small group made up of the coelacanths and lungfish.
Source: Wikipedia: Fish
Image: French grunts (Haemulon flavolineatum), Clinton and Charles Robertson, CC BY 2.0, via Wikimedia Commons.
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