A lab observation notes that a rotifer grinds food using a muscular pharynx containing hard jaws. The observation points to:

The mastax is a muscular pharynx in rotifers containing trophi, which function like jaws for grinding food. This is a diagnostic feature of Rotifera. This MCQ belongs to the Rotifera topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.