PATHOLOGY

Detailed explanation-1: -The flatworms were the first invertebrates to exhibit bilateral symmetry and also the first to develop a central nervous system with a brain.

Detailed explanation-2: -The octopus has the most complicated brain of all the invertebrates. The octopus nervous system has about 500, 000, 000 neurons, with two-thirds of these neurons located in the arms of the octopus. Neurons in the octopus brain are arranged in lobes and tracts that are more specialized than simple ganglia.

Detailed explanation-3: -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).