Diodontidae: Dicotylichthys punctulatus, Diodon spp., Tragulichthys jaculiferus
These strange leathery objects found occasionally on beaches are special internal organs of the porcupinefish. They were once the swimbladders that the fish inflated or deflated to control buoyancy and balance as it moved up and down in the water column. Although many fishes have swimbladders, very few are found on the beach, as they are generally soft and decay quickly. In contrast, those of the porcupinefish are very tough and survive for a long time after the fish has died. In life, when agitated, the porcupinefish can inflate its body via the swimbladder and wedge itself into the reef, making it nearly impossible to swallow by a predator.
Porcupinefish are found in tropical and subtropical seas worldwide and throughout the Indo-west Pacific region, with ten species known from Queensland.