Which of the following animals is triploblastic?

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BlackTom AI · Accepted Answer

Consider the fundamental embryonic tissue organization behind the term 'triploblastic.' 
Option a: Hydra. It belongs to the phylum Cnidaria and develops from two germ layers—epidermis and gastrodermis—so it is diploblastic, not triploblastic. 
Option b: Sponge. Sponges are very primitive multicellular animals (Porifera) that lack true germ layers altogether, hence neither diploblastic nor triploblastic. 
Option c: Earthworm. Earthworms are annelids, which are bilaterally symmetrical and possess three germ layers: ectoderm, mesoderm, and endoderm. This triploblastic condition aligns with their more complex organ systems and a true body cavity. 
Option d: Jellyfish. Like Hydra, jellyfish are cnidarians and exhibit two germ layers (diploblastic) with an outer ectoderm and inner endoderm, lacking a mesoderm. 
Putting these together, the presence of three germ layers is the hallmark of triploblastic development, which is characteristic of organisms such as Earthworms rather than the diploblastic cnidarians or the non-germ-layer sponge. 
In summary, options a, b, and d reflect organisms with either two germ layers or none, while option c demonstrates the three germ layers typical of triploblastic organisms.

BIO 181 (001&002) FALL 2025 3D - Self-Check: Eukaryote Kingdom: Animalia (LO 3D.1, 3D.2, 3D.3, 3D.4)

Which of the following animals is triploblastic?

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