basking shark, large, plankton-feeding shark, Cetorhinus maximus, inhabiting many oceans of the world, especially in temperate regions. Found singly or in schools of up to 100, it spends much of its time on or just below the surface, cruising slowly with its dorsal fin breaking water. It reaches a length of 40 ft (12 m) and weighs up to 8,500 lb (3,900 kg)—among fishes it is second in size only to the whale shark. It feeds by filtering out plankton as water passes into its mouth and out of the gills. Its gill openings are greatly enlarged to accommodate a large volume of water, and its throat is lined with numerous slender structures called gill rakers. These rakers, which are attached to the inside of the gill arches, form a fine mesh that serves as a strainer. The basking shark has a torpedo-shaped body, a nearly symmetrical tail fin, and long, conspicuous gill slits. Its color ranges from gray to black or brown. It is fished commercially, mostly by harpooning; its flesh is used for fish meal and its liver oil for certain tanning processes. It is classified in the phylum Chordata, subphylum Vertebrata, class Chondrichthyes, order Selachii, family Cetorhinidae.
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