They have pore cells
The phylum Porifera comprises the sponges. Sponges are simple invertebrate animals that live in aquatic habitats.
The phylum name Porifera means pore-bearing. Sponges take their name from small holes that cover their bodies.
Epithelial cells form a skin-like layer on the outer surface of a sponge (Fig. 3.20 D). These cells protect and enclose the sponge; they can contract and shorten, moving the sponge body slightly. All sponges are filled with the pores that give the phylum its name.
These pores are sometimes also referred to as ostia, and they provide openings for water, which carries planktonic food and oxygen, to enter the sponge body.