While comparing invertebrate groups, water enters the sea star water vascular system through a sieve-like plate on the aboral surface. The feature being tested is:

The madreporite is a sieve-like plate that connects the water vascular system with the external seawater. It helps regulate fluid entry into the system. This MCQ belongs to the Echinodermata topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.