Page "Tetraodontiformes" Paragraph 2

Most members of this order, except for the Balistidae family, are ostraciiforms, meaning the body is rigid and incapable of lateral flexure.

Because of this, they are slow-moving and rely on their pectoral, dorsal, anal, and caudal fins for propulsion rather than by body undulation.

However, movement is usually quite precise ; dorsal and anal fins aid in manoeuvring and stabilizing.

In most species, all fins are simple, small, and rounded, except for the pelvic fins which, if present, are fused and buried.

Again, in most members, the gill plates are covered over with skin, the only gill opening a small slit above the pectoral fin.