A nervous system is lacking in __________

Sponges belong to the phylum Porifera and exhibit a cellular level of organization. They are primitive multicellular animals that lack true tissues and organs, and therefore do not possess a nervous system.

Hydra (phylum Cnidaria) possesses a primitive nervous system in the form of a nerve net.

Cockroaches (phylum Arthropoda) and gorillas (phylum Chordata) have well-developed nervous systems.

Answer: sponges