Jellyfish Facts

       Jellyfish belong to the phylum Cnidaria.  The jellyfish are free-swimming, and they are found in every ocean, and some of the hydrozoan jellyfish are even found in fresh water.    There are several different cnidarian classes, which include the Scyphozoa, which has over 200 species of jellyfish, the Staurozoa, which has around 50 species of jellyfish, the Cubozoa, which has around 20 species of jellyfish, and the Hydrozoa, which has around 1000-1500 species of jellyfish. 

     Jellyfish are not actually fish.  Their body structure actually looks more like an umbrella.  A group of jellyfish is often referred to as a swarm of jellyfish or a bloom of jellyfish. 

      Jellyfish digest using an area where their nutrients are absorbed, called the gastrodermal lining of the gastrovascular cavity.  Jellyfish do not have a respiratory system.  They do not have complete control over their movement; however, they do have a hydrostatic skeleton that helps them move through contraction and pulsations of their body that is shaped like a bell.  Some of the species of jellyfish will swim constantly, while others just mostly float.  The jellyfish itself is made of more than 90% water, and the majority of their umbrella mass is composed of gelatinous material called mesoglea.  This mesoglea is surrounded by two different layers of epithelial cells which create the umbrella and the subumbrella of the body. 

     It is important to note that the jellyfish does not have a central nervous system or a brain.  Instead, it has a loose network made up of nerves which is located in the epidermis of the jellyfish.  A jellyfish is therefore able to detect stimuli, and this includes the touch of other animals. 

     Jellyfish blooms are typically seasonal, and usually will increase with sunshine and warm temperatures.  Ocean currents may push the jellyfish into these large groups of jellyfish in which there may be up to thousands of jellyfish in one area. 

     Scientists have no idea about how many jellyfish there are living today or how the population of jellyfish has increased or decreased over time. 

     Jellyfish go through two body forms during their life cycles.  The first stage is called the polypoid stage, and this is where the jellyfish has the form of a tiny stalk and feeding tentacles.  At this stage, the jellyfish may live on the bottom of the sea or on floats or boat-bottoms.  It may also be free-floating or attached to freeliving plankton.  Polyps usually have a mouth that is surrounded by tentacles that go upwards.  These jellyfish polyps may be colonial or solitary, and they are capable of budding asexually, creating more polyps.  Most of them are tiny, as they are only a few millimeters of a fraction of an inch in height.  In the second stage, the polyps produce jellyfish asexually, which are known as medusa.  The small jellyfish will withdraw from the polyp by swimming away.  Then they grow by feeding on plankton.  Their umbrella-shaped body is called a bell, and it has tentacles that flow outwards from the border of the bell, and these are used to capture prey.  Some species of jellyfish do not have the polyp stage, so they go directly from jellyfish to jellyfish through development of fertilized eggs. 

     Jellyfish are either male or female.  To reproduce, males and females release sperm and eggs into water where the eggs are fertilized and then mature into new organisms.  In some species of jellyfish, the sperm will swim into the mouths of the female jellyfish which fertilizes the ova in the female's body.  After the fertilization occurs, a larval form which is called the planula will develop from the egg.  This is a small larva which is covered with cilia.  It settles on a firm surface where it develops into a polyp.  This polyp is shaped like a cup and has tentacles which surround one orifice.  It looks much like a small sea anemone.  After a little while, the polyp begins to reproduce asexually by budding.  Some jellyfish species can produce new medusae by budding from the medusan stage. 

     One of the main predators of jellyfish is other species of jellyfish.  Other predators of jellyfish include shark, swordfish, tuna, sea turtles, and salmon.  Jellyfish lifespans usually last somewhere between a few hours and several months. 

      The scyphozoan jellyfish are harvested for food. Most of this harvesting occurs in southeast Asia.  The processing method of the jellyfish involves a 20 to 40 day procedure in which the umbrella and oral arms of the jellyfish are treated with table salt and alum and compressed.  Before salting, the mucous membranes and gonads are removed.  This reduces off-odors, the growth of spoilage organisms, liquidation, and makes the jellyfish more acidic and drier.  This produces a crispier and crunchier texture to the jellyfish when eaten.  In China the processed jellyfish are desalted when they are soaked in water overnight and then eaten raw or cooked.  This jellyfish dish is sometimes served shredded with soy sauce, vinegar and sugar, or in the form of a salad with vegetables.  Japanese people eat cured jellyfish that is rinsed, cut into strips, and then served along with vinegar for an appetizer. 

     Jellyfish sting prey.  They accomplish this using nematocysts, but this only causes reactions in humans by some jellyfish species.  Being touched by a jellyfish can cause a human to feel uncomfortable, and may even require medical assistance, but in a good number of cases the humans have no reaction at all to the touch.  Since the reaction you will have is unknown, it is best not to touch a jellyfish.  If you have been stung by a jellyfish, you may require first aid right away.  There are some species that have stings that can be fatal, and in those that are not fatal, the sting can be very painful.  In the case of serious stings, anaphylaxis can occur, which can lead to death.  To avoid drowning, you must exit the water immediately if you have been stung.  In the case of anaphylactic shock, an antivenin may be required.  First aid involves three goals, which are to prevent any injury to the rescuers, remove tentacles that remain stuck on the victim, and inactivate the nematocysts.  In order to keep the rescuers from being hurt, barrier clothing should be utilized.  By inactivating the nematocysts, further injection of venom will be prevented.  For box jellyfish stings, vinegar should be applied, but this is not a recommended treatment for Portuguese Man o' War stings.  If vinegar is not available, use salt water.  Do not use ammonia, alcohols, spirits, or urine, as this will cause more venom to be released. 

     To remove the stinging cells, you can clean the area of tentacles, jelly, and wetness, which will disable more nematocyst firing.  Rescuers should use gloves to keep themselves from becoming injured.  After the big pieces of jellyfish are removed, you can apply shaving cream to the affected area, and a safety razor, knife edge, or credit card can be utilized to take away remaining nematocysts.  Antihistamines may be needed to control skin irritation.  To get the venom in the skin out, make a paste of baking soda and water and apply a cloth over the sting.  Reapply this paste every fifteen minutes or so.  You can also use ice to stop the spread of the venom until the paste is available.

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