Nervous system
Jellyfish, comb jellies, and related animals have diffuse nerve nets rather than a central nervous system. In most jellyfish the nerve net is spread more or less evenly across the body; in comb jellies it is concentrated near the mouth. The nerve nets consist of sensory neurons, which pick up chemical, tactile, and visual signals; motor neurons, which can activate contractions of the body wall; and intermediate neurons, which detect patterns of activity in the sensory neurons and, in response, send signals to groups of motor neurons. In some cases groups of intermediate neurons are clustered into discrete ganglia.
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."