The blood circulation is closed and there is no heart, in a shark or lancelet.

Of these organisms, the lancelet has a closed circulatory system that does not have a heart. He has one circle of blood circulation, blood flow is carried out by contraction of the abdominal aorta, through which blood moves to the branchial slits. The shark, like all fish, also has a closed circulatory system, and also one circle of blood circulation; but at the same time she, again like all fish, has a two-chambered heart, consisting of an atrium and a ventricle. By contracting, the ventricle (and not the abdominal aorta) drives blood through the vessels.