RESPONSE

Cnidarians nerve nets but no centralized nervous system. Nerve nets are concentrated around the mouth. Polyps and medusa forms of cnidarians have sensory cells in the epidermis that detects chemicals from food and the touch of foreign objects.
In medusae, some groups of sensory cells are organized into simple organs called statocysts and ocelli that arrange around the rim of a medusa’s bell. Statocysts help determine which way is up and ocelli or eyespots detect the presence of light. Coral colonies usually have a basic response to environmental conditions such as light, waves and currents which makes them similar to anthozoans. Take a look at figure 1B (second diagram) in this link for a diagram of a hydra nerve net. http://cas.bellarmine.edu/tietjen/images/cnidarians.htm