What is the main link between the brain and the rest of the body?

Anew organism has been discovered. this organism has a bilaterally symmetric unsegmented body. it's capable of moving on its own with a muscular appendage and is encased in a large shell that seems to be attached to its body. based on this evidence, which phylum would this new animal likely be classified into? a. arthropoda b. echinodermata c. nematoda d. mollusca