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The name sea nettle may also refer to the Pacific sea nettle or West Coast sea nettle (Chrysaora fuscescens) (pictured to the right), another related species that is endemic to the Northeast Pacific Ocean. It is a common coastal species found along the west coast of North America from California to Alaska.
The Atlantic sea nettle is a bell-shaped invertebrate, usually semi-transparent and with small, white dots and reddish-brown stripes. Sea nettles without stripes have a bell that appears white or opaque. The nettle's sting is rated from "moderate" to "severe" and can be pernicious to smaller prey; it is not, however, potent enough to cause human death, except by allergic reaction. While the sting is not particularly harmful, it can cause moderate discomfort to any individual stung. The sting can be effectively neutralized by misting vinegar over the affected area. This keeps unfired nematocysts from firing and adding to the discomfort.
The sea nettle is radially symmetrical, marine, and carnivorous. Its mouth is located at the center of one end of the body, which opens to a gastrovascular cavity that is used for digestion. It has tentacles that surround the mouth to capture food. Nettles have no excretory or respiratory organs. Each sea nettle is free-swimming and can reproduce both sexually and asexually.
Stinging sea nettles are carnivorous. They generally feed on zooplankton, ctenophores, other jellies, and sometimes crustaceans. Nettles immobilize and obtain their prey using their stinging tentacles. After that, the prey is transported to the gastrovascular cavity where it is subsequently digested.
Each nettle tentacle is coated with thousands of microscopic nematocysts; in turn, every individual nematocyst has a "trigger" (cnidocil) paired with a capsule containing a coiled stinging filament. Upon contact, the cnidocil will immediately initiate a process which ejects the venom-coated filament from its capsule and into the target. This will inject toxins capable of killing smaller prey or stunning perceived predators. On humans, this will most likely cause a nonlethal, but nevertheless painful rash typically persisting for about 20 minutes. Some earlier cases of nettle stings from the Philippines reportedly had more severe effects: one account describes a sting causing vascular insufficiency, and another mononeuritis.
Rather than toxic substances, some nematocysts contain adhesion used to entangle or anchor its target.
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Sea nettles have become popular exhibits in many public aquariums, and have been instrumental in educating the public about the mysterious beauty of swimming jellyfishes. The Pacific sea nettle Chrysaora fuscescens was successfully cultured first on a large scale by the Monterey Bay Aquarium in California, where it remains a popular exhibit. It is abundant just offshore from central California to Washington State in the late summer. This species has been traded back and forth between aquariums, so may also be seen on exhibit in aquariums elsewhere in the world, including the American east coast, which may be confusing, since it is not found in the Atlantic Ocean. The Atlantic stinging sea nettle Chrysaora quinquecirrha is also on display now in some public aquariums. The Pacific sea nettle is a warm reddish-brown color, often with no pattern on the outside of the bell (the "exumbrella"), but some individuals have a pale 16-32 rayed star pattern on this brown background. The Atlantic stinging sea nettle is smaller and has more variable coloration, but is typically pale, pinkish or yellowish, often with radiating more deeply-colored stripes on the exumbrella, especially near the margin. There are several other species of sea nettles in the world, but the others are not typically displayed in public aquariums. In the exhibits, jellyfish usually swim against the current in their tank, which is why they usually appear to be swimming downward.
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Pacific sea nettle at the Georgia Aquarium.
Sea nettle jellyfish at the Tennessee Aquarium.
A Pacific sea nettle at the Monterey Bay Aquarium.
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