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How does the mesoderm help form internal body cavities in bilaterally symmetrical animals?
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Animal development
The embryos of many animals appear similar to one another in the earliest stages of development and progress into their specialized forms in later stages.
In bilaterally symmetrical animals, the mesoderm plays a critical role in forming the coelom, or secondary body cavity, which lies between the digestive tract and the body wall musculature. This process occurs through two primary developmental pathways:1
- Schizocoely: Common in many protostomes (such as mollusks and annelids), the coelom forms through the splitting of solid mesodermal masses.12
- Enterocoely: Typical of deuterostomes (such as echinoderms and chordates), the coelom arises as outpocketings from the embryonic gut (archenteron), which then expand to form the body cavity.132
In some vertebrates, the lateral mesoderm splits into somatic and splanchnic layers, creating an intervening space that becomes the coelom as the embryo folds. The formation of this cavity is evolutionarily significant because it allows for the suspension of internal organs via mesenteric layers, preventing gravity from compressing the gut and enabling animals to achieve larger body sizes.42