Cartilaginous fish and jawless fish are quite different to bony fish. These two groups, also known as Chondrichthyes and Agnatha respectively, build their skeletons using cartilage.
A tough but flexible tissue, lighter than bone, that allows them to maintain neutral buoyancy without any need for a swim bladder.
In this video we'll take a look at the differences between jawless fish and cartilaginous fish, and discuss their adaptations and behaviours within the deep sea ecosystem.