Question

which one? fluid - filled cavity surrounded by mesoderm coelom setae parapodia

Explanation:

To solve this, we analyze each term:

• Coelom: Defined as a fluid - filled cavity surrounded by mesoderm tissue.
• Setae: These are bristle - like structures, often for locomotion or protection in some organisms (e.g., annelids), and have nothing to do with a fluid - filled cavity surrounded by mesoderm.
• Parapodia: These are paddle - like or leg - like appendages in some invertebrates (e.g., polychaete annelids) used for locomotion or respiration, and are not related to the described cavity.

So, based on the definition, the term that matches "fluid - filled cavity surrounded by mesoderm" is coelom.

Answer:

coelom