When you see a sea anemone swaying gently underwater it is easy to think that it is a plant. But it is actually an animal that looks and even acts almost like a plant. Most these animals look like exotic flowers and that is the reason they are named after the anemone flower.
How do you pronounce sea anemone?
Sea anemones can be as small as 1.5cm (size of an Australian five cent coin or a US penny) and others can be up to 1.8 meters in diameter. Sea anemones have tubular bodies with a central gut cavity. A jelly-like substance called mesoglea lies between the outer and inner layers of its body. Most sea anemones have an adhesive foot, called a basal disc, with which they attach themselves to a suitable surface. At the other end is an opening referred to as the oral disc. Here are located tentacles covering an opening which serves both as the animal's mouth and anus. Each of these tentacles is armed with numerous cnidocytes which contain stinging nematocysts.
These are often called "true anemones" and a recognised by their adhesive pedal foot with which they attach themselves to hard surfaces and their hollow cylindrical or column shaped bodies. They have an an opening called an oral disc with a mouth on top which is surrounded by tentacles containing stinging nematocysts. These tentacles are non-retractable. About ten types of these anemones play host to anemonefish such as the clownfish, made famous in the movie "Finding Nemo".
These anemones live in a tube that they construct out of a mucus they secrete and threads from nematocyst-like organs called a ptychocysts. They have no adhesive foot pad. Their tube is usually embedded in soft sea sediment. These sea anemones can retract their tentacles. They are usually found living alone and away from other anemones.
Basically, sea anemones are stationary animals that attach themselves to a hard surface and remaining there for their prey to pass by. However they are capable of movement. This locomotion ranges from inconspicuously sliding along, clumpy walking, swimming vigorously or even hitching a ride on the back of another animal such as a hermit crab.
Some sea anemones and hermit crabs establish a lifetime symbiotic relationship where both animals gain an advantage from each other. This particular type of symbiotic relations is referred to as mutualism. This means that each animal is getting a benefit from the other and neither is negatively impacted by the relationship. The sea anemone attached to the hermit crab’s shell acts as the crabs bodyguard. In times of danger the sea anemone may even completely cover the crab with its tentacles and stinging threads to protect it. Most predators wouldn't dare attack this line of defence. The crab in turn provides the sea anemone with scraps from its leftover meals and also provides the anemone mobility by moving it from place to place. By riding on the hermit crab’s back the sea anemone has a better chance of catching plankton, fish and other creatures that may pass by its tentacles. This relationship can be so strong that sometimes young hermit crabs will seek out a young sea anemone an intentionally attach it to its shell where they may become partners for life. As the hermit crab sheds its shell it will move the sea anemone along to its new shell. (See video).
Sea anemone, like their relatives the jellyfish, have specialised cells on their tentacles and around their mouths called cnidocytes (“stinging cells”). Within these are organs called nematocysts (stingers) — the sea anemone’s deadly weapons. Each nematocyst reside in a little silo (like missile silo) with a tiny touch-sensitive hair-like trigger called a cnidocils. Each nematocyst is loaded with a minuscular harpoon around which is wrapped long thread, both of which are covered in toxin. When touched or otherwise triggered the nematocyst fires its deadly harpoon with thread attached. The harpoon will either pierce the flesh or the threads will ensnare its victim releasing toxins (actinotoxins) into its victim soon paralysing, killing or scaring it off in excruciating pain.
Scientists have recently discovered that certain groups of sea anemone do battle with each other groups to protect their territories from encroachment. If an anemone from a rival group enters this territory an army of warrior anemones, who usually live along the perimeter of the group’s territory, swing to action and using special attack tentacles filled with thousands of poisonous nematocysts strike out to repeal the invader. (See video).
There are over 1000 different sea anemones world-wide. Around 40 of these live in the Great Barrier Reef off the north-eastern coast of Australia. Sea anemones prefer shallow water with plenty of sunlight shining through. Sea anemones find a suitable location and attach themselves either to a hard surfaces or soft sea sediment and wait for fish or other prey to swim by to ensnare them with their tentacles. If circumstances arise some sea anemone can up and leave, swimming, gliding or otherwise moving themselves to a new location. Some even attach themselves to a hermit crab and get themselves a mobile home.
Sea anemone are carnivorous animals that consume animal matter. They catch and eat fish, mussels, worms, shrimp, zooplankton crustaceans, and tiny marine larvae.
Sea anemones wait for prey to pass by and then spring into action firing their harpoons at its prey to paralyse and ensnare it. It then grasps its prey with its tentacles and slowly pulls its prey into its mouth and swallows it. Once consumed any waste is also ejected through its mouth as it does not have a separate anus.
Some sea anemones also harbour colonies of tiny symbiotic algae, called zooxanthellae. The sea anemone and zooxanthellae live in a mutually beneficial relationship. The sea anemone provided the algae with a protective environment with plenty of sunlight and nutrients and in return the zooxanthellae uses photosynthesis to produce glucose, glycerol, and amino acids which it shares with the sea anemone.
Lateral fission or budding is where an identical sea anemone sprouts from an adult's side and grows there until it is developed sufficiently to survive on its own. At which stage it detaches from the adult and finds a suitable location to grow on its own. With this budding capability even a piece of a sea anemone is capable of growing to a viable animal.
Sea anemones can also reproduce via eggs and sperm. These are produced in parts of the animals body cavity and ejected through its mouth into the water where eggs and sperm from the same or different sea anemones get fertilised Fertilised eggs develop into free-swimming larvae which soon attach themselves to a suitable habitat and grow into full adulthood. Some sea anemones can live for up to 50 years.
Several types of sea slugs and snails eat the body and tentacles of the sea anemone despite being stung by it. Sea stars such as the leather star seek out and wrap their stomachs around the sea anemone and dissolve it with special digestive juices that ooze from their stomachs. Some crabs nip of tentacles and eat them. Many types of fish nip away at the sea anemone’s tentacles. One of the major predators of the sea anemone is the loggerhead turtle which chomps through the sea anemone and swallows it.
Sea anemone are not considered to be endangered. However, destruction of their habitat, namely the Great Barrier Reef, will definitely impact on their longer term survival.