Multiple choice Which animal was the first one to have three layers of cells (triploblastic)? Hydra Liverfluke Sycon Euplectella Reveal answer Fill a bubble to check yourself B Correct answer Explanation Platyhelminthes are the first phylum to exhibit triploblastic organization, meaning they have three germ layers: ectoderm, mesoderm, and endoderm. Liverfluke is a member of this phylum.