AP BIOLOGY

Detailed explanation-1: -Some organisms, like sea sponges, lack a true nervous system. Others, like jellyfish, lack a true brain and instead have a system of separate but connected nerve cells (neurons) called a “nerve net.” Echinoderms such as sea stars have nerve cells that are bundled into fibers called nerves.

Detailed explanation-2: -Do they have brains? No, jellyfish have no single centralized brain. Instead, they have radially distributed nervous systems that are adapted to their unique body plan.

Detailed explanation-3: -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! Catching prey is also a matter of chance.

Detailed explanation-4: -Step by step answer:Hydra has anatomically one of the simplest nervous systems which is a nerve net formed by the nerve cells present in the epidermis of the Hydra with no sign of a brain.

Detailed explanation-5: -Large concentrations of nerve cells-as in the brain-are not found in these systems, though there may be ganglia, or small local concentrations of neurons. Diffuse systems are found in cnidarians (hydroids, jellyfish, sea anemones, corals) and in ctenophores, or comb jellies.