Do jellyfish have hearts?

Jellyfish do not have hearts, and they also lack brains and bones. Jellyfish are considered plankton and consist of about 98 percent water. The six parts of a jellyfish include the epidermis, an inner layer, the middle jelly, a gastrovascular cavity, an orifice and tentacles.

Due to the large water composition of jellyfish, they mostly evaporate when they leave their natural habitat. The thousands of jellyfish species vary in size from less than an inch to several feet long. Jellyfish are equipped with sensors at the end of their tentacles to detect light and noise. Jellyfish have a long history in the ocean, having appeared on Earth over 650 million years ago.