The correct answer is C. Platyhelminthes.
Platyhelminthes are a phylum of bilaterally symmetrical, unsegmented, soft-bodied invertebrates. They are the simplest animals with a true gastrointestinal tract. Platyhelminthes are found in both marine and freshwater habitats, and some are parasitic.
Nerve cells are found in all platyhelminthes, but nerves are not. Nerve cells are individual cells that are specialized for the transmission of nerve impulses. Nerves are bundles of nerve cells that are organized to transmit nerve impulses over long distances.
In platyhelminthes, nerve cells are scattered throughout the body. They are not organized into nerves. This means that nerve impulses cannot be transmitted over long distances in platyhelminthes.
The other options are incorrect because they all have nerves.
- Porifera are sponges. They do not have true tissues or organs, and they do not have nerve cells.
- Coelenterata are cnidarians. They have a simple nervous system that is organized into a nerve net.
- Nemathelminthes are roundworms. They have a well-developed nervous system that is organized into a central nervous system and a peripheral nervous system.