We had a terrific group of people in our recent course in the Bahamas
Jellyfish have one of the most amazing anatomies of any animal in the world. Interestingly, jellyfish have no brain. Instead they are equipped with a simple nervous system, or nerve network. This network contains receptors which allow jellyfish to detect out side stimuli such as touch, smell, taste, and even some degree of light Đmostly just the difference between bright and dim. Jellyfish are composed of between 95 and 99 percent water, with less than five percent solid mass. They have an outer layer known as the epidermis which covers the body and an inner layer called the gastrodermis to surround the gut. Jellyfish also have a third layer known as the mesoglea. The mesoglea is a jelly like substance located between the epidermis and the gastrodermis. These three layers give jellyfish their jelly like appearance. The coelenteron is a cavity that performs all tasks associated with digestion. However, unlike most animals jellyfish have an incomplete digestive system. This means they have just one opening into the coelenteron which serves as both a mouth and an anus (Gowell, 1993). In order to aid movement jellyfish are also armed with small muscles in the belt region that can be contracted. The belt contractions cause a burst of water which propels the jellyfish (Stidworth, 1990).
Although most jellyfish share a similar anatomy, there are actually 2000 species of jellyfish which vary in size, shape, color, and degree of posed danger. Most jellyfish are nearly clear or a light blue color with sizes ranging from one inch to over a foot in diameter. However, some jellyfish species can grow up to seven feet long (Sharth, 2002).
The most common type of jellyfish is knows as the moon jelly, or Aurelia aurita. The moon jelly can be found in every ocean in the world. It is easy for one to identify because its reproductive organs are a purplish color that can be seen through its transparent body. They are usually about a foot to a foot and a half across with very short tentacles (Sharth, 2002).
The largest type of jellyfish is the lionŐs mane, or Cyanea capillata. LionŐs mane jellyfish are only located in the cool waters of the Atlantic, Pacific, and North and Baltic seas. Other than by its enormous size, lionŐs mane jellyfish can be recognized by their reddish brown color and by their many long tentacles. They are generally six to seven feet long and their tentacles can grow to lengths measuring 200 feet (Sharth, 2002).
Despite the lionŐs manes enormous stature, they are in fact not the most dangerous species of jellyfish. The most deadly jellyfish is the sea wasp, or Chiropsalmus quadrumanus. The sea wasp is most commonly found near Australia, Japan, or the Philippine islands. Although the sea wasp only grows to about six inches, with ten feet long tentacles, it can kill a human in less than three minutes after a sting. In addition to being the most deadly jellyfish, the sea wasp is also the fastest swimmer reaching speeds of five miles per hour. One can usually identify a sea wasp by its clear box-shaped body and long tentacles (Sharth, 2002).
Despite the apparent differences between the species jellyfish generally go through the same reproductive cycle. Jellyfish have arias that develop in the lining of the gut known as gonads. In the gonads the male sperm and female eggs develop. Gonads are generally easy to identify due to their bright array of colors. Once the sperm is fully developed it is released into the coelenteron and out of the body through the mouth. Similarly when the female eggs are developed she does the same thing. However, some of the eggs stick to the mouth of the female jellyfish. Here the sperm is able to fertilize the egg and begin development. After some time the fertilized egg, or embryo, becomes a small creature referred to as a Planula. Equipped with small hairs the Planula is able to travel until it reaches the ocean floor and attaches its self. Once attached to the floor the Planula grows and develops into a Polyp. As they mature the Polyps are able to usually reproduce through a process called budding. This process may go on for a few years. Eventually when many Polyps build up they begin to break off and each one turns into a new jellyfish. Thus many jellyfish can be formed form a single Panula. The final stage of jellyfish life is the Medusa stage. This is where they appear as one would typically envision a jellyfish (Gowell, 1993).
Many people loath snakes, sharks, and spiders due to fear of being bitten. Similarly, a good portion of humans dislike jellyfish out of fear of being harmed. However, contrary to popular belief, jellyfish do not ŇattackÓ humans. Jellyfish sting humans as a result of people swimming into their tentacles or form incidental contact. So why do jellyfish have to be so dangerous? One reason is that jellyfish are primarily carnivorous, meaning they kill and eat other sea animals. In order for an organism composed 95% of water to accomplish such a task they must be equipped with some sort of weapon. This weapon is known as the Cnidoblast. The Cnidoblast contains a stinging device called a nematocyst. Many nematocysts are located on each of the jellies tentacles. When an object comes in contact with a nematocyst they act as small thorns that penetrate the skin and inject toxins. The jelly then uses its tentacles to bring the prey into its mouth opening for consumption. For humans the severity of the sting generally depends on the person or animal and on the species of jellyfish (Gowell, 1993).
One major question I had going into this paper was, what uses are jellyfish to humans and to the ecosystem of the sea? One article I ran across talked about some recent research being done using a jellyfish species known as the cannonball jellyfish. The cannonball is commonly eaten in many Asian countries and consequently it was discovered that it contained large amounts of collagen II. As it turned out collagen II is known to have therapeutic effects when administered orally to patients suffering from rheumatoid arthritis. More research is being conducted but current results appear to be promising (Howard, 2000).
Another aria of research is concerning the GFP, or green fluorescent protein, derived from Atlantic jellyfish. Researchers have found that GFP can be attached to DNA or specific cells to act as a detectable marker. Some uses include being able to seen new cell growth associated with stem cell research (Science News, 1994) and aiding in discovering how and when cretin types of bacteria spread (Research and Development, 1996). Information concerning the ecological significance of jellyfish was slightly harder to come by, possibly due to their stigma of being a general nuisance. However, jellyfish are an important part of the food cycle in the ocean. Many small fish, unharmed by the nematocysts, find sanctuary for predators in the tentacles of jellyfish. Additionally jellies serve as a food source for larger sea creatures, along with preventing over population of organism they feed on (Stidworth, 1990).
In closing I have found that jellyfish are amazing animals. They can live for years before they even look like a jellyfish. Jellyfish remind me of a butterfly of the ocean. Although some are dangerous, they emerge with beautiful colors and delicate bodies. I also feel that with further research jellyfish may end up being more beneficial to humans than we had once imagined.
JellyfishŐs glow reveals headŐs beginning. June 4, 1994. Science News. Vol. 145, No. 23: 358.
Marker works in live cells. September 1996. Research and Development. Vol. 38, No. 10: 281.
Sharth, S. (2002). Sea Jellies from Corals to Jellyfish. New York: Franklin Watts.
Stidworth, J. (1990). Simple Animals. New York: Facts on File.
Gowell, E. T. (1993). Sea Jellies Rainbows in the Sea. New York: Franklin Watts.
Howard, J. (2000). AU Research Shows Jellyfish Could Treat Rheumatoid Arthritis. Retrieved form http://www.auburn.edu/.
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