Final answer:
Arrow worms with no food in their digestive system risk starvation as they rely on ingestion of prey for energy. They possess a complete digestive system that allows for efficient digestion and continuous feeding compared to simpler digestive systems.
Step-by-step explanation:
Arrow worms, known as chaetognaths, possess a complete digestive system which functions efficiently by allowing continuous feeding and digestion. When there's a lack of food, like in many other organisms, arrow worms would typically experience a decrease in available energy for sustaining bodily functions. This can eventually lead to starvation if the situation persists. Unlike some parasites, such as tapeworms, which absorb nutrients directly across their body wall, arrow worms require ingestion of prey organisms to obtain energy. In organisms with a complete digestive system, efficiency in digestion is increased due to specialized organs. This system provides advantages over simpler forms, like the flatworm's gastrovascular cavity, where the ingestion and excretion occur through the same opening.