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(Diodon hystryx), a fish of the family Diodontidae of the order Tetraodontiformes. Its almost spherical body, which measures up to 60 cm long, is olive green with small dark spots on the back and tail. Covered with sharp, massive, sometimes long (up to 5 cm) spines with broad roots, the porcupine fish appears to be armor-clad. The movable spines can be flattened or raised like those of a porcupine. The stomach walls, like those of puffers, can be greatly stretched. Porcupine fish are widely distributed in the tropical and temperate waters of the Atlantic, Indian, and Pacific oceans. A relatively immobile fish, it inflates itself and surfaces with raised spines and its underside facing upward when attacked by a predator. The sharp exposed edges of the enlarged jawbones compensate for the absence of teeth and are used to crush shells and to bite off branches of coral polyps. The flesh of the porcupine fish is poisonous.