Question

i have a digestive cavity with one opening, and have tentacles. i am a hydra. options: echinoderm, cnidarian, arthropod, mollusk

Explanation:

Hydra is a Cnidarian. Cnidarians have a gastrovascular cavity (digestive cavity) with a single opening (mouth/anus) and tentacles with cnidocytes. Echinoderms (e.g., starfish) have different body plans, arthropods have exoskeletons and jointed appendages, and mollusks (e.g., snails) have a different body structure. So the correct classification for hydra is Cnidarian.

Answer:

B. Cnidarian