Free-swimming, motile colonial or medusoid zooids are observed in which cnidarian group?
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Answer: B. Medusae
Explanation
Medusae are free-swimming motile jellyfish-like zooids typical of certain cnidarian life cycles. Their bell-shaped morphology enables propulsion through open marine waters via muscular contractions. This motile form contrasts with sedentary benthic polyps in species exhibiting metagenesis. Cnidarians include jellyfish corals and sea anemones characterized by radial body symmetry. The medusa stage typically reproduces sexually by releasing gametes into the surrounding water column. Specialized stinging cells called cnidocytes help these marine organisms capture prey efficiently.
Marine biologists study cnidarian life cycles to understand ocean food web dynamics and population blooms. Jellyfish stings pose health risks to swimmers frequenting coastal marine waters worldwide. Fossilized cnidarians provide valuable clues about ancient marine ecosystems and evolutionary history. Polyps are sessile benthic cnidarian forms attached permanently to solid underwater substrates. Options suggesting both medusae and polyps are incorrect because polyps are strictly non-motile. Options citing none of these are wrong because medusae accurately describe the motile zooids.
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