Which of the following is an example of cnidarians?

• A. Jellyfish
• B. Sponges
• C. Earthworms
• D. Planarians

Answer: (A)

Cnidarians are defined by specialized stinging cells called cnidocytes and a body plan built around radial symmetry with two tissue layers and a single gastrovascular cavity. Jellyfish fit this group perfectly: they have tentacles armed with cnidocytes to capture prey, a diploblastic body organization (outer epidermis and inner gastrodermis) with a jelly-like mesoglea in between, and a simple gut that serves for digestion and circulation. Sponges lack true tissues and nerves, so they’re not cnidarians. Earthworms and planarians are bilaterian animals with more complex organ systems and bilateral symmetry, not the diploblastic, tissue-layered setup seen in cnidarians.