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Sea anemone
Colonial zebra anemone from East Timor
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Subclass: Hexacorallia
Order: Actiniaria
Suborders

Endocoelantheae
Nyantheae
Protantheae
Ptychodacteae

Diversity
46 families
The 49th plate from Ernst Haeckel's Kunstformen der Natur, 1904, showing various sea anemones classified as Actiniae

Sea anemones are a group of water dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. As cnidarians, sea anemones are closely related to corals, jellyfish, tube-dwelling anemones, and Hydra.

Contents

Anatomy

A sea anemone is a plant like flower polyp, attached at the bottom to the surface beneath it by an adhesive foot, called a pedal disk, with a column shaped body ending in an oral disk. The mouth is in the middle of the oral disk, surrounded by tentacles armed with many cnidocytes, which are cells that function as a defense and as a means to capture prey. Cnidocytes contain nematocyst, capsule-like organelles capable of everting, giving phylum Cnidaria its name.[1] The cnidae that sting are called nematocysts. Each nematocyst contains a small vesicle filled with toxins (actinoporins) an inner filament and an external sensory hair. When the hair is touched, it mechanically triggers the cell explosion, a harpoon-like structure which attaches to organisms that trigger it, and injects a dose of poison in the flesh of the aggressor or prey. This gives the anemone its characteristic sticky feeling. the sea anemone eats small fish and shrimp.

The poison is a mix of toxins, including neurotoxins, which paralyzes the prey and allows it to be moved to the mouth for digestion inside the gastrovascular cavity. Actinoporins have been reported as highly toxic to fish and crustaceans, which may be the natural prey of sea anemones. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators.[citation needed] Anemonefish (clownfish), small banded fish in various colors, are not affected by their host anemone's sting and shelter from predators within its tentacles.[2]

The external anatomy of anemones is quite complex. There is a gastrovascular cavity (which functions as a stomach) with a single opening to the outside which functions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut. A primitive nervous system, without centralization, coordinates the processes involved in maintaining homeostasis as well as biochemical and physical responses to various stimuli. Anemones range in size from less than 1¼ cm (½ in) to nearly 2 m (6 ft) in diameter.[3] They can have a range of ten tentacles to hundreds.

The muscles and nerves in anemones are much simpler than those of other animals. Cells in the outer layer (epidermis) and the inner layer (gastrodermis) have microfilaments that group into contractile fibers. These fibers are not true muscles because they are not freely suspended in the body cavity as they are in more developed animals. Since the anemone lacks a skeleton, the contractile cells pull against the gastrovascular cavity, which acts as a hydrostatic skeleton. The anemone stabilizes itself by shutting its mouth, which keeps the gastrovascular cavity at a constant volume, making it more rigid.

Life cycle

Asexual reproduction of sea anemone via budding.

Unlike other cnidarians, anemones (and other anthozoans) entirely lack the free-swimming medusa stage of the life cycle: the polyp produces eggs and sperm, and the fertilized egg develops into a planula that develops directly into another polyp.

Anemones tend to stay in the same spot until conditions become unsuitable (prolonged dryness, for example), or a predator attacks them. In that case anemones can release themselves from the substrate and use flexing motions to swim to a new location.

The sexes in sea anemones are separate for some species while some are hermaphroditic. Both sexual and asexual reproduction may occur. In sexual reproduction males release sperm to stimulate females to release eggs, and fertilization occurs. Anemones eject eggs and sperm through the mouth. The fertilized egg develops into a planula, which settles and grows into a single polyp. Anemones can also reproduce asexually, by budding, binary fission (the polyp separates into two halves), and pedal laceration, in which small pieces of the pedal disc break off and regenerate into small anemones.

In media

  • The rock band Alien Ant Farm repeat the refrain "A sea anemone, you're my enemy" in their song "Stranded".
  • In episode 54 of the podcast Jordan, Jesse Go! entitled "I Dream of Jordan", at about 38:30 hosts Jesse Thorn and Jordan Morris detail the similarities between a sea anemone and co-host Jordan.
  • In the Pixar movie Finding Nemo, clownfish Nemo and Marlin live in a sea anemone.
  • In the Owl City song "The Bird and the Worm", singer Adam Young sings the lyric: "With fronds like these / Well, who needs anenomes?"

See also

Gallery

References

  1. ^ Campbell N. & J. Reece (2002). Biology (6th ed ed.). San Francisco: Pearson Education. 
  2. ^ Fagatele Bay NMS: Clownfish and Sea Anemone
  3. ^ [1]

External links


Simple English

Sea anemone
Scientific classification
Kingdom: Animalia
Phylum: Cnidaria
Class: Anthozoa
Subclass: Hexacorallia
Order: Actiniaria
Diversity
46 families
File:Common
A common clownfish in a sea anemone. The fish lives in a symbiosis with the anemone

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Sea anemones are Cnidarian animals that live in the sea. They are polyps, one of the basic forms of the phylum. They are predatory animals, which paralyse their prey with stinging nematocysts which fire a harpoon-like structure which delivers a dose of neurotoxins. To eat the fish, or crustacean, they move the prey into their stomach. Anemones are sessile (stay in one spot), but they can move if necessary.

The anemones have an oral disk on the top of its body. The Sea Anemone’s head is located in the middle of the oral disk, and the tentacles surround the oral disk. The pedal disc is situated on the bottom of the Sea Anemone









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