Cnidarians do not have a brain, however, they do have sensory cells which tell them information that is necessary for survival. When it comes to muscles, Cnidarians don't stand for much. Their muscles consist of an outer layer of longitudinal fibers at the base of the epidermis and an inner layer of circular fibers at the base of the gastrodermis. However, the lack of muscles does not impair the mobile Cnidarians' movement. They use jet propulsion by sucking water into the gastrovascular cavity and then spitting it out in a strong spurt of water to move themselves.
Cnidarians reproduce in different ways depending on whether they are polyps as adults, or medusae.
All medusae have sexual reproduction. Cnidarians exhibit open-water fertilization, in that the male organisms release sperm into the water and it is collected by the female, who then releases the fertilized eggs. The fact that Cnidarians have free swimming larvae allows the sessile creatures to spread their colonies rather than pile up on top of each other.