puffer, common name for some tropical marine fish of the family Tetraodontidae. The puffers and their allies, the boxfish, the porcupinefish, and the ocean sunfish or headfish, form an odd group (order Tetraodontiformes). The puffers, or swellfishes, named for their ability to inflate their bodies to three times normal size, are found all along the Atlantic coast, e.g., the northern puffer ( Sphaeroides maculatus ), and in the Pacific. Their prickly skin is exaggerated into stout spines in the porcupinefish (family Diodontidae) and the spiny boxfish, or burrfish, which are also able to inflate themselves. Like the puffers, they feed on marine invertebrates. The ocean sunfish, or headfish (family Molidae), occurs widely in all seas, although it prefers warmer waters. Its appearance is that of a huge head with fins attached, as its body does not taper. It moves clumsily and is usually seen basking in the sun. The ocean sunfish is one of the largest of all fishes, the record weight being about one ton (900 kg). It is harpooned for sport; except for the oil from its liver, it is of little value as food. Puffers and their allies are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Tetraodontiformes.