Family Diodontidae

Body globular and highly inflatable by swallowing water or air to deter predators; scales modified into large sharp spines with large subdermal bases; teeth fused into single beak-like plate in each jaw; jaws without median suture. Dorsal fin and anal fin more or less rounded and set far back on body; no pelvic fins; no fin spines. Gill opening a small vertical slit immediately before pectoral-fin base. Lateral line inconspicuous. Vertebrae 18–23.