the smooth trunkfish (Rhinesomus triqueter) is a fish in the family Ostraciidae. It is commonly found on coral reefs where its bony carapace and its ability to release toxins when excited protect it from predators. It feeds on small invertebrates such as mollusks, worms, crustaceans, etc.
The caption reads in the original French:
Le coffre triangulaire. (Ostracion triqueter, Linn.)