Sea Butterfly photographed by Ingo Arndt. Tiny marine shelless snails known as sea butterflies take many forms, including heart-shaped, such as this species in Antarctica's Weddell Sea. via National Geographic
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.