A lab observation notes that gills, anus, and excretory openings of many molluscs open into a space under the mantle. The observation points to:

The mantle cavity is the space between mantle and visceral mass. It often houses gills and receives openings of digestive, excretory, and reproductive systems. This MCQ belongs to the Mollusca topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.