Final answer:
Arrow worms have a complete digestive system with a separate mouth and anus.
Step-by-step explanation:
Arrow worms, also known as Chaetognaths, have a complete digestive system. A complete digestive system consists of a digestive tract with two openings, one for the mouth and one for the anus. This allows for a more efficient process of digestion, as food can be continuously taken in while waste is eliminated. Other invertebrates, such as jellyfish and flatworms, have incomplete digestive systems with only one opening that serves as both the mouth and anus.