Primitive nervous system of coelenterata and echinodermata?

The primitive nervous system of coelenterata (such as jellyfish and sea anemones) and echinodermata (such as starfish and sea urchins) is characterized by a decentralized network of nerve cells called a nerve net.

In coelenterates, the nerve net is composed of interconnected neurons that are spread throughout the body. These neurons are responsible for coordinating basic sensory and motor functions. The nerve net allows for simple reflex responses to stimuli, such as contracting in response to touch or light.

Echinoderms also possess a nerve net, although it is more developed compared to coelenterates. The nerve net in echinoderms is concentrated in the oral region and radiates outwards to the arms or rays. This nerve net allows for coordination of movement and response to external stimuli.

Both coelenterates and echinoderms lack a centralized brain or ganglia, and their nervous systems are relatively simple compared to more advanced organisms.