Unlike bony fish, the sharks have a complex dermal corset made of
flexible collagenous fibres and arranged as a helical network
surrounding their body. This works as an outer skeleton, providing
attachment for their swimming muscles and thus saving energy. A similar
arrangement of collagen fibres has been discovered in dolphins and squid. Their dermal teeth give them hydrodynamic advantages as they reduce turbulence when swimming.
A few of the larger species, such as the shortfin mako, Isurus oxyrinchus, and the great white, are mildly homeothermic
- able to maintain their body temperature above the surrounding water
temperature. This is possible because of the presence of the rete mirabile, a counter current exchange mechanism that reduces the loss of body heat.