Marie BuendiaJellyfish are cool, amazing, and beautiful creatures and in my opinion, very sensuous, that's if you've ever just watched a jellyfish move . It usually drifts with the ocean current, however it can also move on it's on accord by sucking water into its mouths and pushing it out again. This gives it a slow pulsating movement, that is almost calming to watch. On the Fresh-Water-Jellyfish website , one can watch a movie of a jellyfish in high-speed motion. There are over two hundred different species of jellyfish, ranging in shape and size. They inhabit every ocean in the world. Though most inhabit coastal waters, there are some deep sea swellers. Most jellyfish are almost transparent, but some have the ability to glow beautiful colors in the dark waters. Some amazing pictures of jellyfish can be found on the Discovery Online, Jellyfish: My Life as a Blob webpage .
Phylum and Class:
Jellyfish belong to phylum: cnidaria, and class: scyphozoa. They are invertebrates just like sea anemones and coral (6) . Cnidaria is derived from the Greek work "cnidos" which means "stinging nettles." "Cnidarians are characterized by stinging cells called nematocysts or cnidocytes, which when disturbed eject a barbed thread and often poison as well" (8) .
They are made up of over ninety-five percent water. The other five percent is three to four percent salts and one to two percent proteins. Their bodies have three main parts: 1) the round umbrella (or bell) shaped body, 2) tentacles which have the nematocysts and sting the prey, and 3) oral arms, also called flaps, which they used to eat their prey.(3) 
The umbrella shaped part of the body is made up of two cell layers. The outer layer is the ectoderm and the inner layer is the endoderm (8)  In-between these two layers is there is a jelly-like substance called mesoglea. Some scientists have cut this jelly-like substance and found that it stays firm, but don't know why (1) . The amazing thing about jellyfish is that they lack a heart, a brain, bones, and eyes. Jellyfish can smell, taste, and detect light. They do have some nerve cells which help them to react to food or danger and to move. These sensors also tell them if they are moving away or towards light and if they are heading up or down (3)  They have special sacs which are similar to the sacs in the inner ear of humans. These are located on the bell rim and they aid the jellyfish maintain balance. These sacs stimulate nerve endings when a jellyfish has shifted too far to one side and the simulation contracts muscles that re-orient the jellyfish. Also located on the bell rim are light sensing organs so the jellyfish can detect light and dark. They also have chemoreceptors, which enable the jellyfish to smell and taste things (3) .
Jellyfish breathe by absorbing oxygen from the water through the surface of their outer layer. They also release carbon dioxide by their surface. Jellyfish do need to eat too, but since they don't have a mouth, how do they get food? Instead of a mouth they have an 'oral cavity', similar to a mouth(3) . The oral cavity is located where the oral arms meet the round umbrella-shaped body. This is the one and only opening on the jellyfish body. It leads to stomach chambers. In the particular species, Craspedacust sowerby, the oral cavity leads to four different stomach chambers (1) . Because there is only one opening, the jellyfish actually gets rid of its waste through the same hole in which it takes in its food. Jellyfish usually feed on zooplankton, which are small drifting animals. These include juvenile fish, other jellyfish and larval crustaceans (3) . They use their tentacles to trap their food.
Their tentacles contain the stinging cells called nematocysts. "The stinging cell consists of a capsule with a sensory hair, a lid, and an interior nematocyst which actually stings, captures, and subdues prey. When the sensory hair is triggered by another animal's movement, the nematocyst fires from the capsule, much like a harpoon. A nematocyst fires in only a few milliseconds, making this cellular process one of the fastest in nature (3) . Even after a jellyfish is washed up on the shore and dead, as long as the tentacles are still moist, nematocysts are still capable of stinging.
There are smaller fish which are unaffected by the nematocysts, and they actually swim and live in the tentacles of a jellyfish for protection. Larger sea dwelling creatures such as the sunfish and leatherback seaturtles are unaffected by the stinging cells and usually feed on jellyfish. Jellyfish also feed on other jellyfish. Even people have found certain dishes they can make out of jellyfish and it has become quite a delicacy.
Jellyfish are really old, over six hundred fifty million years (3) . They have been around longer than sharks and appeared long before dinosaurs lived. There is actually a fossil record of a jellyfish. Scyphozoans are rare as fools because their bodies are composed of mostly water. The fossilized jellyfish must be preserved under very special and unusual conditions. One such case is the "Solnogen Limestone of Bavaria, Germany, [which] is a body of rock which has yielded many fossils of exceptional preservation."(7)  Collections of this rock can be found in the Senckenberg Museum in Frankfurt, Germany. Life Cycle:
The average jellyfish lifespan is a year. A well studied jellyfish, the aurelia, or moon jellyfish are separately sexed jellyfish. The male release sperm into the water with enter the female's oral cavity and fertilize her eggs (6) . These now fertilized eggs, zygotes, hang out for a while on the oral arms and develop into round, flat larvae. Developing into larvae, also called the planula stage, they have beating hairlike cilia which help them swim and find a place to settle (9)  When they find a place they then attach themselves to it, usually the ocean floor, and enter the polyp stage. One single polyp can split itself into a whole stack of flattened polyps. These flattened polyps enter the next stage in development. They break off and become the young jellyfish which resemble the adults, they are called ephyrae. These ephyrae start to develop tentacles and oral arms and grow into the adult which will start the reproduction cycle once again.
Exciting News about Jellyfish Today:
There are jellyfish that don't sting. They actually lost their ability to sting. In a lake called the Jellyfish Lake, people can actually swim among thousands of these pulsing, gelatinous creatures. Located in the Pacific Republic of Palau, the body of water is a landlocked saltwater lake which trapped the jellyfish a million years ago when a submerged reef rose from the sea and blocked them going out.10 "Over the centuries, with no predators or need to capture food, they gradually lost their long tentacles and their ability to sting" (10) . These jellyfish have come to rely on the sun for food. Meaning they rely on the symbiotic algae the live within their tissues for food. These jellyfish use their light- sensing organs to swim towards the sun to ensure that the algae receives enough sunlight for photosynthesis. The algae releases nutrients which the jellyfish absorb (a href="#3">(3). It has been observed that if these algae die, then the jellyfish will continue to consume its own tissues which may even lead to its death (11)  Jellyfish lake gets thousands of visitors each year to swim among these graceful creatures.
If jellyfish are in the news today it is probably because they stung some beach- goers. The jellyfish sting can cause rashes, extreme pain, and rarely, death. Children in the middle-eastern countries are known to play with washed up jellyfish, (playing catch with them) until they are numb all over.
Organizations such as the Monterey Bay Aquarium  and the Monterey Bay Aquarium Research Institute  are known for their extensive research on jellyfish. One can go to their website to find out more at: http://www.mbari.org and http://www.mbayaq.org.
2) A swimming jellyfish , from Brookings/Harbor High School, Oregon
3) National Aquarium in Baltimore  (links to other pages with more facts on jellyfish)
4) The Jellyfish Page 
5) Jellyfish: My Life as a Blob , from Discovery Online (amazing and beautiful pictures)
6) Introduction to the Scyphozoa , from University of California Museum of Paleontology
7) Fossil Record of the Scyphozoa , from University of California Museum of Paleontology
8) Introduction to the Cnidaria , from University of California Museum of Paleontology
9) Life Cycle of the Moon Jelly , from the National Aquarium in Baltimore
10) Jellyfish Lake , from the Nature Conservancy
Comments made prior to 2007
most amazing thing happend in a dream of mine, i remember a part of it.
we were at a beach in the sand, there were a lot of people , like the
hole of humanity, we all saw,feld a jellyfish comming twords the beach,
we all dove in , swimming to the jellyfish, I got there first.. what
happend next is hard to explain.. as I came to put my finger on
it, I forgot who I was, but I knew everything there is to know. I was
more awake in this dream then i am in real life.. also a sort of
power,light,magic glow came for the jellyfish.
I dont know what this dream means but I feel like what happend was important for me and humanity .. why the jellyfish.. i dont know. but I still think about the dream everyday. I cant let go, I want to know ... Thomas, 2 May 2006