• Norwegian: helhoder


Holocephali (="complete heads") is a class of mostly extinct species of cartilaginous fish. A single gill opening in each side gives the head a undivided appearance, in contrast to the sharks and rays (class Elasmobranchii) which have two or more gill openings. The large eyes are typical for deep sea species. Other common features are a big head and a long tail.


The order Chimaeriformes, the chimaeras, is the only surviving group in this class. There are extensive evidence of numerous prehistoric species, but the relationship with the modern chimaeras are poorly understood, due to lack of complete fossils. The rabbit fish is the only chimaera a scuba diver is likely to encounter in Norwegian waters.