A learner makes a note: a jellyfish swims freely with an umbrella-shaped body and tentacles hanging downward. The missing scientific idea is:

The medusa is the free-swimming cnidarian form. It is bell- or umbrella-shaped and is prominent in many jellyfish life cycles. This MCQ belongs to the Cnidaria topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.