Since the tissue layers are very thin, they provide too little power to swim against currents and just enough to control movement within currents. Parts of the Antarctic seabed are covered by anemones, and they occur near the deep-sea hot vents.
Most obtain the majority of their food from predation but some, including the corals Hetroxenia and Leptogorgiadepend almost completely on their endosymbionts and on absorbing dissolved nutrients. The sessile asexual colony has two types of polyps, shown in Figure.
Spirocysts do not have cilia. Cnidocytes[ edit ] These "nettle cells" function as harpoonssince their payloads remain connected to the bodies of the cells by threads.
Each medusa has either several testes or several ovaries in which meiosis occurs to produce sperm or egg cells. The gametes are released into the surrounding water, and after fertilization, the zygote develops into a blastula, which soon develops into a ciliated, bilaterally symmetrical planula larva.
Ptychocysts are found only in the order Cerianthariatube anemones. They also secrete the jelly-like mesoglea that separates the layers. These cells are located around the mouth and on the tentacles, and serve to capture prey or repel predators.