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| [Note Guidelines] Photographer's Note |
This shot was taken at the New England Aquarium in Boston.
Named after a terrestrial flower, the anemone, sea anemones form a group of water-dwelling, filter feeding animals of the order Actinaria. As a cnidarian, the sea anemone is closely related to coral and jellyfish. Other close relations to the sea anemone are the solitary, tube-dwelling anemones and the hydras.
An anemone is basically the typical polyp: a small sac, attached to the bottom by an adhesive foot, with a column shaped body ending in an oral disc. The mouth is in the middle of the oral disc, surrounded by tentacles armed with many cnidocytes, which are unique cells that function as a defense and as a means to capture prey. Cnydocytes contain cnidae, capsule-like organelles capable of everting, giving phylum Cnidaria its name. 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, that fires 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. Interestingly the clownfish is immune to an anemone's sting. The poison is actually a mix of toxins, including neurotoxins, which serve to paralyze and capture the prey, which is then moved by the tentacles to the mouth/anus 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.
The internal anatomy of anemones is very simple. There is a gastrovascular cavity (which functions as a stomach) with a single opening to the outside which fuctions as both a mouth and an anus: waste and undigested matter is excreted through the mouth/anus. 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. They can have a range of 10 tentacles to hundreds.
ref:http://en.wikipedia.org/wiki/Sea_anemone |
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