[Campbell Biology P.730] Which statement correctly describes the body cavity and its lining ... | Practice Question

Which statement correctly describes the body cavity and its lining in triploblastic animals?

  • A: Coelomates possess a body cavity completely lined by tissue derived from ectoderm.
  • B: Hemocoel, also known as a pseudocoelom, is a body cavity not completely lined by mesoderm-derived tissue, as seen in roundworms.
  • C: Acoelomates, like earthworms, lack a body cavity between the digestive tract and outer body wall.
  • D: The presence or absence of a coelom or hemocoel is a good indicator of phylogenetic relationships.

Explanation

The text states that a hemocoel 'forms between the mesoderm and endoderm' and animals with only a hemocoel 'once were called pseudocoelomates'. A pseudocoelom is a body cavity not completely lined by mesoderm-derived tissue. Roundworms nematodes are mentioned as having only a hemocoel. Coeloms are completely lined by mesoderm. Acoelomates like planarians lack a body cavity. The presence/absence of these cavities is not a good phylogenetic indicator.