Sea Anemones are a group of marine predators related to corals and jellyfish. They are classified within the Cnidaria phylum and often look like large, floating sea flowers. A great majority of these creatures live out their lives attached to a rock through a basal disc at the bottom of their bodies. They have a very simple digestive system, in which they capture prey through the mouth, digest it, and then excrete waste through the same opening. Most sea anemones are venomous users of nematocysts, like jellyfish.
Sea Anemones have a complex internal anatomy consisting of a number of unusual features. Their incomplete digestive system is one such feature for which they have adapted a unique response to. The anemone nerve system is also unusual, in that sea anemones do not appear to have any specialized organs for sense – no eyes, touch-sensitive cells or the ability to smell. Unlike other cnidarians, most sea anemones do not spend a portion of their life in a medusa stage where they freely swim and float about until finding an appropriate place to attach themselves to. They will stay attached to the same spot until conditions force them to move.
These particular cnidarians can reproduce both sexually and asexually. In sexual reproduction, males release sperm in the water and, thus, stimulate females into releasing eggs, and fertilization occurs in the open water between the two individuals. The resulting fertilized egg then turned into a planula that grows into a single polyp that then attaches itself to a nearby rock. In asexual reproduction, sea anemones can bud extra individuals, reproduce by binary fission, or through regeneration of lacerated parts of the pedal disc. Large enough parts cut off of a sea anemone will regenerate into a new individual.
The sea anemone features an oral disk that it uses to capture and eat prey. Because the anemone is largely immobile, it will attach itself to a rock and wait for unsuspecting prey to travel too close. When this happens, the venomous nematocysts will discharge, rendering the prey helpless as the anemone consumes it. It is not uncommon for sea anemones to foster symbiotic relationships with certain fish, algae and crustaceans, some of which are responsible for bringing food sources to the anemone. Some algae directly provide oxygen and glycerol to the organism.