AP BIOLOGY

Detailed explanation-1: -Unlike higher animals, the hydra does not have any grouping of nerve cell bodies. In other words, there are no ganglia. The hydra does have specialized cells for touch and chemical detection. Like the hydra, the jellyfish has a nervous system characterized by a series of interconnected nerve cells (a nerve net).

Detailed explanation-2: -Jellyfish have no such central place; in fact, they have two nervous systems. A large nerve net controls swimming and a small nerve net controls all other behaviors, including feeding and spasm response (briefly curling into a ball).

Detailed explanation-3: -Although their nervous system is relatively simple, a common misunderstanding is that all jellyfish have only a diffuse nerve net in which neurons are found homogeneously spread apart. In fact, most jellyfish species show some degree of neuronal condensation that serves as an integrative nervous system.

Detailed explanation-4: -So how do they function without a brain or central nervous system? They have a basic set of nerves at the base of their tentacles which can detect touch, temperature, salinity etc. Since they don’t have a brain, they depend on automatic reflexes in response to these stimuli!

Detailed explanation-5: -Most cnidarians, such as those of the genus Hydra, have what is called a nerve net-a meshlike system of individual and separate nerve cells and fibres dispersed over the organism. Species of Hydra have two nets, one located between the epidermis and the musculature and the second associated with the gastrodermis.