Which of the following groups of animals do not possess a nervous system?

A. Porifera
B. Cnidaria
C. Platyheminthes
D. Nematoda

Correct Answer: Option A

A. Porifera

Explanation

Porifera are ‘pore bearing’ organisms, commonly known as sponges, are the only multicellular organisms without a nervous system. Their response to stimuli is by a contraction in their bodies.