Sponges are simple animals, and invertebrates. They are
multicellular, but have no digestive, respiration, or nervous
systems. A large number of pores are present on a sponge's body
surface and indeed throughout their bodies, allowing seawater to
circulate through the sponge's body cavities, providing food and
oxygen to the cells.
Sponges are mostly found in seas but a few are present in lakes, streams and rivers. They are attached to stones in their adult life. Sponges may reproduce sexually or by budding, and the sexual form may include free-swimming larvae.
Sponges help clean the ocean. Some protect themselves with spikes that they have in their bodies. When they are dead and dried, they are good for scrubbing and cleaning.