Fun:Sponge

A sponge is an animal that lives in the sea. They feel very spongy.

Significance to the evolution of multicellular life
This experiment shows that single-celled organisms may have formed multicellular ones. First get a sponge, and chop it up into several small pieces. These pieces are then forced through a sieve so fine it separates the individual cells that make up the animal. Then, view it through a microscope to see the individual cells clumping together. After waiting for a while, the cells will clump to form the original multicellular organism. This does not work with goats.

Furthermore, if you were to do the same experiment, but mix up the cells of different species of sponges, the sponges would all assemble into their separate species.