How could you possibly have fun with a jellyfish?

Sponges, of course, can have fun with just about anybody. They are, after all, the life of the oceanic party - a living, flow-through filtration system that can deliver the party treats quicker than Dominos. The delivery system is provided by specialized cells called choanocytes. Choanocytes are flagellated, and the action of the flagella create a current bringing food-laden water into the sponge. Choanocytes are also equipped with a collar of microvilli around the base of the flagellum. Food particles carried with the water are trapped in this collar, ingested, and passed along to other cells for utilization within the body of the sponge. While sponges take on a vareity of body plans, the utilization of choanoctyes to move water and collect food is universal. Modern single-celled choanoflagellates are structured similarly, suggesting that they may share a common ancestor with sponges.

Take a look at the movement of water through sponges as demonstrated here. Be forewarned, the music's not as cool...