In which animal the nerve cell is present but the brain is absent?

Step-by-step solution

Hydra which belongs to the phylum coelenterata has nerve cells but no brain. Its nervous system consists of nerve cells and their processes. Sponges are the only multicellular animals without a nervous system. They do not have any nerve cells or sensory cells. Earthworms have a simple nervous system. The cerebral ganglion is connected to a ventral nerve cord that runs the length of the body. Cockroach has in total 9 ganglia in number. Each ganglion of the nerve cord is formed by the fusion of two ganglia except the