Final answer:
In arrow worms, the coelom internally mirrors the body regions with the protocoel, mesocoel, and metacoel.
Step-by-step explanation:
In arrow worms, the coelom internally mirrors the body regions. This means that the body cavity, called the coelom, is present and mirrors the different regions of the body. The coelom is divided into three parts: the protocoel, mesocoel, and metacoel. Each of these regions within the coelom has specific functions and helps with the organization of the internal organs.