Diploblastic versus Triploblastic Body Plans
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State
A diploblastic animal forms two germ layers, ectoderm and endoderm; a triploblastic animal forms three, adding mesoderm between them.
Show
A jellyfish is diploblastic, lacking mesoderm-derived organs; an earthworm is triploblastic, with mesoderm-derived muscle and internal organs.
Watch for
Mesoderm's presence, not general body size, is what separates diploblastic from triploblastic lineages — some triploblastic animals are smaller than some diploblastic ones.