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Animals develop either two or three embryonic germ layers. The animals that display radial, biradial, or rotational symmetry develop two germ layers, an inner layer (endoderm or mesendoderm) and an outer layer (ectoderm). These animals are called diploblastic, and have a nonliving middle layer between the endoderm and ectoderm. More complex animals (usually those with bilateral symmetry) develop three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three tissue layers are called triploblasts.

c. jellyfish : Jellyfish are radially symmetrical and just diploblastic.

a. sea star: Seastar is triploblastic because they are a part of the phyla Echinodermata and its organs are developed from the mesoderm layer.

b. shrimp, d. insect : Both shrimp and insects belong to phylum arthropoda. Arthropods have 3 germinal layers and are triploblastic.