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Aquatic: Sea anemones

Find, identify & discuss the insects of SANParks
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francoisd
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Aquatic: Sea anemones

Unread postby francoisd » Fri Jun 20, 2008 3:09 pm

Very difficult for us "normal folk" to really get down under the ocean to take photos of the marine fauna and flora so I'll post photos with this of anemones I photographed at Two Ocean Aquarium.

Numerous anemones occur around our coastline including the national parks bordering the ocean

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Some info

A sea anemone is a small sac, attached at the bottom to the surface beneath it by an adhesive foot, called a basal disc, 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 cells that function as a defense and as a means to capture prey. Cnidocytes 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, 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 poison is a mix of toxins, including neurotoxins, which paralyze 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. In addition to their role in predation, it has been suggested that actinoporins could act, when released in water, as repellents against potential predators. Certain clownfish are not affected by their host anemone's sting.

The internal anatomy of anemones is simple. 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. They can have a range of 10 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 grouped together into contractile fibers. These 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 stability for this hydrostatic skeleton is caused by the anemone shutting its mouth, which keeps the gastrovascular cavity at a constant volume, making it more rigid.

Although not plants and therefore incapable of photosynthesis themselves, many sea anemones form an important facultative symbiotic relationship with certain single-celled green algae species which reside in the animals' gastrodermal cells. These algae may be either zooxanthellae, zoochlorellae or both. The sea anemone benefits from the products of the algae's photosynthesis, namely oxygen and food in the form of glycerol, glucose and alanine; the algae in turn are assured a reliable exposure to sunlight and protection from micro-feeders, which the anemones actively maintain. The algae also benefit by being protected due to the presence of stinging cells called nematocysts, reducing the likelihood of being eaten by herbivores. Most species inhabit tropical reefs, although there are species adapted to relatively cold waters, intertidal reefs, and sand/kelp environments.

Information taken from Wikipedia
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restio
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Unread postby restio » Fri Jun 20, 2008 7:24 pm

Beautiful photos, FD - thanks! :D
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yoda
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Anenome

Unread postby yoda » Fri Jan 09, 2015 10:34 pm

After our Kruger trip, we went down to Cape Town.
My family enjoy going to the beach, myself, not so.

So I had to amuse myself while the rest enjoyed the sun.
Spent a few hours climbing over the rocks and looking in the rock pools

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