How do porocytes control water entering calcareous sponges?

In calcareous sponges, porocytes are specialized, flattened granular cells located on the outer body surface that contain the pores necessary for water to enter the sponge. These cells function as a regulatory mechanism for the sponge's water-current system.12

Porocytes are capable of contracting, which allows the sponge to close these pores in response to unfavorable environmental conditions or the presence of toxic and irritating substances. By controlling the expansion and contraction of these pores, the sponge can regulate the flow of water into its internal system, ensuring that the organism can protect itself while maintaining efficient filter-feeding processes.13