A lab observation notes that in a flatworm cross-section, tissue fills the region between the gut and body wall instead of a coelom. The observation points to:

Acoelomate flatworms have parenchyma or mesenchymal tissue filling the space between the digestive tract and body wall. This confirms absence of a true body cavity. This MCQ belongs to the Platyhelminthes topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.