While comparing invertebrate groups, hydra digests food in a central cavity that has a single opening used for both ingestion and egestion. The feature being tested is:

Correct Answer: B

gastrovascular cavity

Cnidarians possess a gastrovascular cavity with one opening. It functions in digestion and distribution of nutrients, but it is not a complete digestive tract. This MCQ belongs to the Cnidaria topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.