A diagram in the course handout shows that in a dissected annelid, the body cavity is fully lined with mesodermal tissue. Identify the related structure or process.

A true coelom is completely lined by mesoderm. This body cavity provides space for organs, allows more complex organ systems, and can function as a hydrostatic skeleton in many invertebrates. This MCQ belongs to the Body cavities topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.