Comparative embryology helped clarify the relationships among major groups of animals. Bilaterians, for example, are:

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Bilaterians are triploblastic, meaning they have three germ layers during embryonic development. This is a key characteristic that distinguishes them from diploblastic animals, which only have two germ layers. Bilaterians may be further classified as coelomates or acoelomates, depending on whether or not they have a body cavity called a coelom. They may also be further classified as protostomes or deuterostomes based on the pattern of their embryonic development.

Comparative Embryology Helped Clarify the Relationships Among Major Groups of Animals