Jellyfish system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. A loose network of nerves called a "nerve net" is located in the epidermis. Although traditionally thought
Cyanea (jellyfish) Cyanea (jellyfish) Cyanea is a cosmopolitan genus of stinging jellyfish, primarily found in northern waters of the Atlantic and Pacific Oceans. The same genus name has been given to a genus of plants of the Hawaiian lobelioids, an example of a "parahomonym" (same name, different kingdom). The taxonomy of "Cyanea" species is not fully agreed upon. Some zoologists have suggested that all species within the genus should be treated as one. However, in the North Sea at least, the lion's mane jellyfish and the blue jellyfish appear as distinct species. "Cyanea" may be a species complex of recently diverged species.