No, members of the phylum Cnidaria do not have a complex nervous system. Instead, they possess a simple nerve net. This nerve net is a decentralized network of neurons that allows for basic responses to stimuli.
Cnidarians, which include organisms like jellyfish, corals, and sea anemones, have a more primitive structure compared to animals with complex nervous systems. Their nerve net enables them to react to environmental changes, capture prey, and coordinate movements, but it lacks the centralized control seen in the brains of more complex animals.
The simplicity of their nervous system is suited to their lifestyle, allowing them to function effectively in their aquatic environments without the need for advanced processing capabilities. This adaptation has worked well for them over millions of years, allowing Cnidarians to thrive in various marine habitats.