Q. What is circulation?
Circulation is the movement of substances like gases within blood vessels and nutrients and cavities throughout the organism.
Q. Do all animals have a circulatory system?
Not all animals have a circulatory system Cnidarians, Poriferans, nematodes and platyhelminthes (in these there are the pseudocoelom fluid but no vessels) are avascular animals. Echinoderms do not have true circulatory systems whichever.