Sea anemones

Actiniaria

Storlek: From 2 mm up to 1 m in diameter, most species in between 1-5 cm.
Lifespan: Up to 60 years.
Food: Zoo plankton, fish and crustaceans.

Animals that resemble mushrooms or plants

Sea anemones may look like plants or mushrooms, but they are an order of aquatic animals within the group of cnidarians. The cnidarians also include the relatives of the anemone, such as corals and jellyfish. Sea anemones range in size from 5 mm to 100 mm in diameter, and can have many different colours, such as red, pink, yellow, white, orange, green, blue and brown.

Most sea anemones inhabit the tropical reefs, but there are some species that have also adapted to colder waters with sandy environments and tidal reefs. There are about 1,200 species of anemones worldwide, and about 30 of these can be found along the west coast of Sweden.

Eats and poops through the same hole

Anemones are shaped like something known as a polyp. They have a cylinder (tube) form, consisting of a body, a foot and a crown with tentacles. In the body there is a cavity, like a sack, which acts as the stomach of the anemone. An opening which serves as both mouth and anus leads to the stomach. The many tentacles of the anemone move back and forth in the water. The tentacles are covered with burning nettle cells that protect against predators, and paralyse and capture prey such as shrimps and plankton. The tentacles are used to move food to the mouth.

The foot disc at the base of the anemone’s body is used to attach to rocks, seaweed or similar near the bottom. A few species, however, are completely free-swimming in the water. The foot disc does not remain attached to the substrate, allowing the anemone to move. Movement, however, is extremely slow.

Stinging tentacles benefit other species

Many anemones live in symbiosis, meaning cooperation, with other species such as fish, crabs and algae. Fish are protected from predators by the stinging tentacles of the anemones. The clownfish species, famous from the film Finding Nemo, has developed a special mucus layer in its skin that protects it from the venom-lined tentacles of the anemones. The anemones benefit from getting access to food, by eating bits of small fish, algae and worms left as scraps by the clownfish.

An anemone living in symbiosis with a crab, attaches itself to the shell of the crab with the help of its foot disc. The anemone protects the crab from predators and in return receives food by eating the scraps left by the crab, such as mussels, fish, shrimp and jellyfish.