‘Suitcase fish’

One night we were sitting at a bar of a beach club with a international group of friends. One of them was talking about a dive she took that day and how she could approach a Trunk fish real close.
She couldn’t come up with the English name of the fish. In dutch it is called a koffervis (koffer can be translated to suitcase), so she came up with the translation ‘Suitcase fish’…