The aptly named Ping-pong tree sponge (Chondrocladia lampadiglobus) is a carnivorous sponge. Those ping-pong ball looking things are covered in tiny spicules which the sponge uses to catch tiny crustaceans.
Coral (Stichodactyla haddoni, Ukwiał dywanowy) - These Carpet Anemones are my favorites. Clown fish will love them too. Word of caution if your clown fish was breed/raised in captivity it most likely will not know / use an Anemone for a home.
This animal, the Leafy Seadragon, is a Threatened species. They are threatened by collecting for use in Chinese medicine (and by habitat loss). Just one more example of the beautiful natural world exploited by idiotic traditional Chinese cruelty.
Sea Anemone Photograph by Oriana Poindexter. A close relative of coral and jellyfish, anemones are stinging polyps that spend most of their time waiting for fish to pass close enough to get ensnared in their venom-filled tentacles.