Do jellyfish have a heart and a brain?

Jellyfish do not have specialized digestive, osmoregulatory, central nervous, respiratory, or circulatory systems.

A jellyfish does not have a brain or central nervous system, but rather has a loose network of nerves, located in the epidermis, which is called a "nerve net". A jellyfish detects various stimuli including the touch of other animals via this nerve net, which then transmits impulses both throughout the nerve net and around a circular nerve ring, through the rhopalial lappet, located at the rim of the jellyfish body, to other nerve cells.