Coelenterates, also known as cnidarians, are a group of animals that include jellyfish, corals, and sea anemones. One of their primitive features is radial symmetry, meaning that their bodies are organized around a central axis, like the spokes of a wheel.

Radial symmetry is a characteristic of simple, primitive body plans, and it allows coelenterates to respond to stimuli from all directions.

The other options are not correct:

A. Dorsal mouth: Coelenterates have a mouth surrounded by tentacles, but it's not necessarily dorsal (on the back).

C. Bilateral symmetry: This is a more advanced body plan, where the body can be divided into left and right halves. Coelenterates do not have bilateral symmetry.

D. A false foot: This is a characteristic of some other animal groups, like mollusks, but not coelenterates.