This means that, while sponges are multicellular, the cells are more or less independent of one another. It is possible, for example, to force a sponge through a sieve that separates the sponge cells from one another. The individual cells that result can live independently for a while and eventually rejoin and organize themselves in groups of cells that have a structure similar to the original sponge. Most sponges are marine but a few live in freshwater. For example, Folsom Lake is home to freshwater sponges.
Sponges are filter feeders.
This means that they remove microscopic organisms like bacteria, yeast, spores, and protozoans from the water that flows through their body. To be a successful filter feeder, an organism must be in moving water or must be able to move water through its body. In many sponges, there is a hollow sea water-filled area in the center called the spongocoel. Collar cells each have a flagellum. The movement of the flagella of all the collar cells in the sponge creates a current that draws water-containing food into the sponge through the ostia.