Yellow boxfish (Derek Keats / CC BY)
Boxfish (Ostraciidae) are characterized by bony polygonal plates that give them the appearance of a box or suitcase. They have small mouths with conical, stout teeth. Boxfish are poor swimmers. Acanthostracion quadricornis can reach a length of 60 centimeters (24 inches). Most species are smaller, though. Ostracion lentiginosus and some other boxfish species secrete a highly toxic substance (ostracitoxin) when disturbed, so divers should avoid touching them.
Some species venomous.