Sponges come in a variety of shapes, colors and sizes. Generally, they can be classified as by shape as: tubes, vases, barrels, balls, ropes, encrusting, and boring sponges among others. They are multicellular animals whose design usually allows the sponge to draw water into the sponge, which provides the sponge food and oxygen, and then  filters out the water.  The water exits out of the sponge’s interior through excurrent openings or oscula.

Sponges can provide habitat for a variety of sea creatures.  For instance, it is not uncommon for seahorses to hide among rope sponges.  

Other animals, like lobsters, may hide under ball sponges.

As someone who takes a lot of pictures underwater, it is not unusual for me to look inside as many sponges as I see, just to try to find the various creatures that are often hiding, in, around or just near sponges.

So next time you are out diving, be sure to look in and around the sponges you see. You never know what you might find.