Nervous system
Nervous systems are found in most multicellular animals, but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges, placozoans, and mesozoans, which have very simple body plans. The nervous systems of the radially symmetric organisms ctenophores (comb jellies) and cnidarians (which include anemones, hydras, corals and jellyfish) consist of a diffuse nerve net. All other animal species, with the exception of a few types of worm, have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to around 300 billion cells in African elephants.
Jellyfish as food
In China, some species of jellyfish in the Rhizostomae order caught in coastal areas have been utilized as a source of food and ingredient in Chinese cuisine for over 1,700 years. Cannonball jellyfish ("Stomolophus meleagris") and jelly blubber ("Catostylus mosaicus") are edible species of jellyfish. When live, the cannonball jellyfish contains toxins that can cause cardiac problems in animals (including humans). "Rhopilema esculentum" and "Rhopilema hispidium" are edible jellyfish, and are the most common ones consumed in China, Japan and Korea. Additional edible jellyfish species include "Aurelia aurita", "C. orsini", "Dactylometra pacifica", "Hispidium spp.", "Lobonema smithi", "Lobonemoides gracilis" and Nomura's jellyfish ("Stomolophus nomuria"). Desalted ready-to-use jellyfish are low in calories and contain hardly any fat, about 5% protein and 95% water. They do not have much flavor, and may be used to add additional texture and mouthfeel to various dishes. In some areas of Asia, jellyfish is "associated with easing bone and muscle pain."