Marine Science 2016 Edition

Page 280 Chapter 11 Figure 280.1 A sea anemone (Photo Mike Sugden) Figure 280.2 Sea anemone internal structure Figure 280.3 The anemone and the clownfish form a symbiotic relationship called mutualism. (Photo Murray Waite) Class Anthozoa Sea anemones Sea anemones illustrate some of the features of the phylum Cnidaria. The body plan is arranged in a circle with two cell layers and stinging cells on the tentacles (see Figure 280.1). The tentacles are connected to a mouth which leads down to a hollow gut (the coelenteron) which is where food is digested (Figure 280.2). Wastes are then ejected out of the mouth. Sea anemones can move by sliding on their basal disc or by somersaulting from place to place. They reproduce by growing small buds on their sides or by producing eggs and sperm from inside their gut. They can also retract during low tide or to eat their prey using strong retractor muscles located in the body wall. A special relationship Some anemones have a symbiotic relationship with clownfish. These fish hide amongst the tentacles to avoid predators. They can do this because a coating of mucous protects them against the nematocysts of the anemone. The fish benefit by having a safe place to hide and in return the clownfish chases away fish which feed on the anemone eg butterfly fish. This type of symbiosis is called mutualism and is discussed further in Chapter 15.