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Triggerfish skeleton. Coloured X-ray of a triggerfish (family Balistidae). Its name originates from its ability to erect the first two dorsal spines (upper left), which can then lock or unlock, preventing the fish from being swallowed by predators or being pulled out of its nest. The fish's head extends into a snout with strong jaws containing eight teeth on the lower jaw and six on the upper jaw. Triggerfish are found in the Atlantic, Mediterranean and Indo-Pacific. They grow to between 30-75 centimetres. (KEYSTONE/SCIENCE PHOTO LIBRARY/D. ROBERTS) === ===