Body shape in representatives of the ten extant families of tetraodontiforms. Composit of figures from Tyler, 1980, © James C. Tyler

The Order Tetraodontiformes comprises approximately 350 species of highly derived acanthomorph fishes notable for their exceptional degree of diversity in morphological structure, shape, size, and way of life.  They are found in temperate and tropical marine waters worldwide, although a few families are absent in the eastern Pacific and the Atlantic, and some species are found in the fresh waters of South America, Africa, and south-east Asia.  They are grouped in ten well-defined extant families, each of whose monophyly is unequivocal; however, questions remain about how some of these families are interrelated.  The families and their respective general habitats are as follows:

Triacanthodidae (spikefishes), deep-water, bottom-dwelling (one species bathypelagic), absent in the eastern Pacific, the most basal extant linage of tetraodontiforms;

Triacanthidae (triplespines), shallow continental bottom waters, absent from the Atlantic and the eastern Pacific;

Balistidae (triggerfishes) and its sister group Monacanthidae (filefishes), often associated with coral or rocky reefs and surrounding sand and sea grass beds, with a few pelagic species;

Aracanidae (boxfishes, absent from the Atlantic and the eastern Pacific) and its sister group Ostraciidae (trunkfishes), associated with coral and rocky reefs and surrounding shallow bottoms (some trunkfishes with pelagic juvenile stages; one trunkfish species matures and spawns pelagically);

Triodontidae (three-tooth puffers), a single extant species, in Indo-western Pacific deep bottom waters;

Tetraodontidae (puffers or fugu) and its sister group Diodontidae (porcupinefishes), associated with coral and rocky reefs and shallow bottoms, with a few pelagic species;

Molidae (ocean sunfishes), three well-known pelagic species in oceans worldwide, and perhaps one or two more localized regional taxa confined to southern oceans or Austral-Asia.