Coelom

Definition

A coelom is a fluid-filled body cavity completely lined by mesodermal tissue. It provides space for the development and suspension of internal organs and contributes to the complexity of animal body plans.

5 Must Know Facts For Your Next Test

1. Coeloms allow for the development of more complex organ systems compared to acoelomates.
2. Animals with a true coelom are called coelomates, whereas those without it are termed acoelomates or pseudocoelomates.
3. The presence or absence of a coelom is an important characteristic in animal classification.
4. In coelomates, the coelom can develop through two processes: schizocoely (splitting within the mesoderm) or enterocoely (outpocketing of the gut).
5. Examples of coelomate animals include annelids, mollusks, arthropods, echinoderms, and chordates.

Review Questions

• What is a coelom and how does it differ from a pseudocoelom?
• Why is the presence of a coelom significant in animal classification?
• Name two processes through which a true coelom can develop.

Related terms

Acoelomate: An animal that lacks a fluid-filled body cavity.

Pseudocoelomate: An animal with a body cavity that is not entirely lined by mesodermal tissue.

Mesoderm: The middle layer of embryonic tissue that develops into muscles, bones, and other organs in triploblastic animals.