Ostia are small holes on the surface of sponges that allow water to enter and exit the spongocoel.
The spongocoel is the interior chamber of a sponge that discharges through the osculum.
It belongs to the Phylum Porifera and they are usually found in the sea, however, a few species may also be found in freshwater. Example: - Leucosolenia (simple sponge) and Euplectella (venus flower basket).