Nervous System

Despite lacking a brain, hydra possesses nerve cells. It is a member of the Coelenterata phylum. Nerve cells and associated activities make up its nervous system. The brain is missing, yet sensory cells are still intact. Sponge's nervous system is absent. There are no nerve cells in them. The neurological system of an earthworm and cockroach is made up of a circumcenter nerve ring and a solid, double, midventral nerve cord containing ganglia.