Whether there is a heart depends mainly on the type of circulatory system. Invertebrates, such as earthworms and ants, are open-loop animals. The blood in the body cavity has no real circulation system, so there is no heart, but not all invertebrates have no heart. Animals in mollusks have two hearts, which are very different from vertebrates, but the prototype of closed circulatory system has also appeared. As for the brain, invertebrate phylum is replaced by ganglion, and the real brain appears with the appearance of this chorda, so it is a unique structure of chordates.