How do bivalves near active deep-sea vents obtain food? Food enters a flatworm’s body cavity through a muscular tube called a flame cell. pharynx. ganglion.coelom. Some flatworms have clusters of nerve cells that control the nervous system. Each cluster is called a(an) ganglion.brain.ow do bivalves near active deep-sea vents obtain food? Food enters a flatworm’s body cavity through a muscular tube called a flame cell. pharynx. ganglion.