Sponges are living animals that feed by pulling currents of water through openings (oscula) in their bodies and filtering out small food particles from the water.
Although many sponges are marine, they also live in freshwater lakes and streams, often in shallow water. Their appearance varies greatly, with some being simple encrustations or cushions and others being branched.
Freshwater sponges grow attached to a substrate, which may be a rock or submerged branch, and many have a strong green color due to the presence of chlorophyll from algae living inside them.
Wisconsin sponges grow to their maximum size by late summer, early fall. Sponges form seed-like overwintering capsules called gemmules.
The sponge has a skeleton composed of tiny needle-like elements of silica called spicules. The gemmules and spicules of each species have a distinctive look, shown on this website in highly magnified images taken with a scanning electron microscope. Species traits can be seen with a regular light microscope too, so you may want to try identifying sponges with your biology class. The large-sized spicules are called megascleres and the small-sized ones microscleres. Spicules from the gemmule are called gemmoscleres (hooked in this scanning electron micrograph).