Answer: Mesoderm-lined cavity.
- A Mesoderm-lined cavity
- B a cavity with no lining at all
- C only an ectoderm-lined space
- D a plain pseudocoelom pocket
Correct answer: A. Mesoderm-lined cavity
Explanation: A true coelom is a cavity lined by mesoderm.
Moving across the animal phyla, body organisation becomes progressively more complex: from no symmetry and cellular organisation (Porifera) through radial/diploblastic (Cnidaria), bilateral/acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), to a true coelom with full organ systems (Annelida and beyond).
Concept context
Phylum-level classification of the animal kingdom from Porifera to Chordata, based on body symmetry, coelom, and segmentation. One of the most example-heavy chapters for NEET.