ABSTRACT
The most noticeable characteristic of the cnidarian nervous system, the nerve net, has become a symbol of the nervous complexity of the group. This greatly underestimates the morphological and physiological capabilities of cnidarians. A nerve net, in isolation, has significant integrative capabilities. But the cnidarian nervous systems consist of multiple interacting conducting systems (some diffuse nerve nets) and are capable of controlling rich behavior repertoires. In many cnidarians, the compression of nerve nets gives the appearance and function of directional nerves, while the collection of multiple, interacting, conducting systems in the nerve rings (NRs) of hydromedusae form a centralization that functions like the central nervous systems of other animals. In scyphozoan and cubozoan medusae, rhopalia combine sensory structures with complex neuropils to form integration centers that function much like ganglia. The two forms of centralization in medusae perform the functions of central nervous systems but under the constraints of radial symmetry.
