Dorsal Fin of Holocephali
The living holocephalans include three families in the order Chimaeriformes. An erectile first dorsal fin with a spine and a long, low spineless second dorsal Chimaeras protect themselves from such threat by having the large toxic spine located just in front of the first dorsal fin. In addition to inhibiting marine based predation, the spines have also been known to cause serious injury to deep-sea fishermen that often get lodged in lower limbs and hands.
About the Animal
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 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. Jaws holostylic supporting the upper jaw completely fused to cranium. The hyoid arch complete and unmodified branchial arches below cranium. The internal skeleton of cartilage, Their scales do not continue to grow once fully formed. 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.