Multiple choice

Which animal was the first to have three layers of cells (triploblastic)?

  1. Hydra

  2. Liverfluke

  3. Sycon

  4. Euplectella
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B Correct answer
Explanation

Liverfluke (a platyhelminth/flatworm) represents one of the earliest triplobastic animals, possessing three germ layers (ectoderm, mesoderm, and endoderm). In contrast, poriferans like Sycon and Euplectella are diploblastic or lack true tissue layers, while coelenterates like Hydra are diplobastic with only two germ layers. The development of mesoderm in flatworms allows for more complex organ systems.

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