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 ganglion in the 7th segment. Related Theory The nervous system of the cockroach is spread throughout the body. The head holds a bit of nervous system while the rest is situated along the ventral (belly-side) part of its body. So, if the head of the cockroach is cut off, it will still live for as long as one week. Caution Here brain word implies any kind of nerve tissue agglomerations/ganglion. All the options given lacks brain.