Marine anemones are predatory invertebrates that are water-dwelling and closely related to jellyfish, corals and hydra. These interesting creatures literally come in nearly every color, size and shape and certainly add quite a display and a bit of charm to any aquarium.Most species are considered polyps, attaching themselves to a surface by their adhesive foot while others are pelagic. This variety of marine anemone has a pedal disc and a gas chamber that permits them to float around the water upside down.