Sponges continually pump water through the ostea into an internal system of canals and expel it from the osculum, trapping food and removing oxygen from the water. They use collar cells in these canals to flip flagella, creating the pumping action that forces the water through their structure and trapping tiny bits of food.
The Ocean Research Group says sponges are filter feeders that can consume particles as small as bacteria as well as much larger ones. They consist of an outer layer of flat epithelial cells, a middle gelatinous layer with cells that are able to migrate throughout the layer, and an inner layer containing the flagellated and collar cells.
Sponges, once thought to be plants, are animals and require oxygen to live. They transfer waste, including carbon dioxide, to the water as it passes through the canals as a part of their respiration process.
Reference.com reports there are more than 4,500 known species of sponges, all marine, with the exception of one family of freshwater sponges. They prefer shallow, temperate water, where most sponges attach themselves to rocks and live the remainder of their lives. Freestanding sponges, such as the barrel sponge, grow large enough to fit a human inside.