 They are primarily made of an elastic fibre called octopus arterial elastomer, with stiffer collagen fibres recruited at high pressure to help the vessel maintain its shape without over-stretching.Shadwick and Nilsson theorized that all octopus blood vessels may use smooth-muscle contractions to help move blood through the body, which would make sense in the context of them living under water with the attendant pressure.The elasticity and contractile nature of the octopus aorta serves to smooth out the pulsing nature of blood flow from the heart as the pulses travel the length of the vessel, while the vena cava serves in an energy-storage capacity.