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Four Cnidarian Classes

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State

Cnidaria divides into four classes: Anthozoa, polyp-only, including corals; Scyphozoa, true jellyfish; Cubozoa, box jellyfish; and Hydrozoa, a varied group.

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A reef-building coral is an anthozoan colony of polyps; a box jellyfish, a cubozoan, carries venom potent enough to matter medically.

Watch for

Cubozoan venom potency varies sharply by species — not every box jellyfish poses the danger a few species do.