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Jellyfish like corals come in many different shapes and sizes. The bell, which for lack of a better term is the head, is where the activity takes place. All jellyfish have radial symmetry, which means itŐs the same in all directions from a center point. This allows the jellyfish to respond to any situation from any direction. Most range in size from an inch to a little over on foot. In some cases however, there have been jellyfish that had a bell that was seven feet across. Even more amazing in the lengths that the stinging tentacles can reach, ŇSome Jellyfish can reach lengths greater than one hundred feet.Ó (Buddin)
Jellyfish have two distinct phases during their life cycle. People recognize the adult version which is called a medusa. It is umbrella shaped with tentacles hanging down on the side. In its early phase itŐs a polyp which a stalk with tentacles floating up until it breaks off and becomes what we would recognize as a jellyfish. Jellyfish are not asexual and they reproduce when the male ejaculates his sperm out the one hole he has got into water that is surrounded by female jellyfish; which sucks it up where fertilization commences. The larva, called the planula, hangs out in the jellyfish to form for a little while then falls to the ground where it settles and develops into a polyp. (Wikipedia) throughout its life in both stages it feeds itself by objects that pass by and ensnares in the tentacles.
All the tentacles have stinging cells, technically called nematocysts,
Each cell contains a tiny harpoon which, when triggered by touch or movement, shoots into the prey and delivers a debilitating toxin. (Weston)
This action when triggered is one of the fast biological responses ever discovered. ItŐs so fast that it has been clocked at 3/1000 of a second. Nematocysts are found on the tentacles and a single one can have thousands of nematocysts. The amount of tentacles that hang and the number of stinging cells in each tentacle vary between species. The
most toxic and potentially lethal jellyfish is the box jelly. Contact with certain other objects like skin, fish, etc. set off a chemical reaction that fires off the nematocyst. Jellyfish arenŐt attackers because their bodies donŐt allow for quick movements. (Weston) Therefore, victims of jellyfish stings received their sting through accidental contact on their part.
Some jellyfish like the cannonball jelly (Stomolophus meleagris) arenŐt considered dangerous only a nuisance. ThatŐs because these jellyfish donŐt have any tentacles only, ŇA gristle-like feeding apparatus formed by the joining of the oral arms.Ó (Buddin) furthermore they donŐt grow much bigger than 8 inches in diameter. If you say jellyfish, the picture that most often comes to mind is one of the moon jellies (Aurelia aurita). These jellyfish have tentacles and are similar in size to the cannonball jelly, but has the ability to fire nematocysts that restrict pain only to the exposed area. The lionŐs mane (Cyanea capillata), like all cyanea, has a relatively moderate sting that requires more attention then the previous encounters. The jellyfish that one would least like to encounter is the sea wasp (Chiropsalmus quadrumanus). Otherwise known as the box jelly due to the four corners where the tentacles hang, this jellyfish is one of the most powerful swimmers and carries a toxin that can kill a grown man in less than thirty minutes.
Something that has scientists confused is how it is that sea turtles can eat such creatures without being subjected to the damages of the toxins. Sea turtles must have a way to make the toxin ineffective towards them. As luck, for the jellyfish, may have it, jellyfish populations are on the rise. Some, like Claudia Mills, have attributed this to be a symptom of mankindŐs impact on marine life. As Davidson said in his book, sea turtle population has drastically reduced in the last century, so the predators of jellyfish are becoming scarcer. Along with that, large blooms, in which are thousands of jellyfish floating along together are reproducing causing lots of ecological concern for coastal cities. Further evidence for jellyfish population increase includes the fact that jellyfish feed on the same prey that over fished creatures do. ŇJellyfish feed on the same kinds of prey as adult and young fishes, so if fish are removed from the equation, jellyfish are likely to move in." (Wikipedia) High oxygen levels arenŐt as big of a concern for jellyfish as they are for fish, so they can feed in waters that have eutrophication. All of this evidence, plus increased nutrient content in waters by openings from agricultural products points toward a time where jellyfish blooms are commonplace. Some places like the Gulf of Mexico and the Adriatic Sea have experienced these blooms, which causes disturbances in fishing, deterred tourism and increased amounts of stings. (Wikipedia)
Jellyfish happen to be incredibly simple creatures of the sea. Yet, without a brain they are still capable of containing incredible wonders such as the reaction speed of the nematocysts. They have lived and survived on earth much longer than humans have been around and the likelihood of an extinction happening soon is relatively small. So we had better find a way to live with them so as to prevent injury to ourselves and make sure that they still leave enough room for the fish in the sea.
Buddin, Elizabeth. Sea Science: education series from the Marine Resources Divition. 2000, (www.dnr.state.sc.us/marine/pub/seascience/jellyfi.html)
Mitev, Angel. Box jellyfish, Boxfish, Deadly sea wasp, 2000. Thinkquest team, (library.thinkquest.org/C007974/2_1box.htm)
Palmer, A.R. and Geissman J. Geological Society of America (GSA) 1999 Geologic Timescale, Nov. 2002 (www.ucmp.berkeley.edu/help/timeform.html)
Weston, Paula. Creation Archive; Volume 25 Issue 4: Jellyfish, 2003. (www.answersingenesis.org/creation/v25/i4/nobrain.asp)
Box Jellyfish. Species Đ Chironex Fleckeri (www.barrierreefaustralia.com/the-great-barrier-reef/jellyfish.htm
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