JELLYFISH ARE NOT FISH. Now that we have cleared that up, I can proceed. Jellyfish (or Jellies) are the Cnidria phylum. The Cnidria have one defining feature and that is that they sting. The Jellyfish make up the largest, ‘non-polyp’ proportion of the Cnidria and are found in every Ocean on Earth. They are thought to be the oldest multi-cellular animal and have been on Earth for over 700 million years. During the 700 million years, the jellyfish have been extremely successful. They have adapted to live in both the deep sea and shallow waters; in both fresh and seawater!
Rather than eating like a fish would, the jellyfish absorbs its nutrients from its surroundings. To do this, the jellyfish may sting its prey (usually plankton, crustacean, small fish and other jellies!) and then begin to use digestive enzymes to break down the organic matter. The jellyfish is also able to ‘breath’ passively because oxygen diffuses from the seawater, across the jellies’ cell membrane and into its cells. Unlike fish, the jellyfish do not have much control over their mobility. The jellyfish moves by a complex mechanism (one which is not fully understood!) which uses water as a propulsion ‘jet’ which allows them moves in one direction. The jellyfish will allow water to pass through it and then eject quickly in one direction. This allows the jellyfish move in the opposite direction.
Sometimes jellyfish can aggregate together to form a larger, multi-organism colony. These colonies can become extremely large: some can cover over 50 M of the sea! Perhaps the most famous of these colonies is the ‘Portuguese Man of War’ which is often mistaken for a single jellyfish. The individual ‘zooids’ in the colony, despite being an individually specialised organism, are unable to live independently of the colony. The name ‘man of war’ actually comes from an 18th Century sailing ship because the man of war is thought to resemble the shape of the ship when its on full sail.
What should you do if you get stung by a jellyfish? Well if you’re Monica from F.R.I.E.N.D.S you may opt to get urinated on. This would actually cause more damage than good! Urinating on a jellyfish sting is likely to release more venom into the person because the barbs are likely to be disturbed and therefore pierce the skin more. There is not one sure-fire method to help jellyfish stings. The most common treatment is to use a cloth with dampened vinegar because this will help deactivate the nematocysts (the stinging parts!) and thus stop the venom. However, this will make things worse in the aforementioned man of war jelly because its nematocysts are more dangerous in acidic conditions!
The jellies are home to own on the ‘biggest’ organisms on earth. The lion-mane jellyfish can grow up 120 ft long! This is much longer than a blue whale and is only beaten by some species of ribbon worm! Jellyfish are often seen as a delicacy in some Asian countries. Dried Jellyfish is particularly popular in Japan and South Korea. It is dried because this will help stop the organism from spoiling. If they were not dried, they would spoil within a few hours. I myself can testify to this. I have seen jellyfish (although thankfully never stung!) on a beach near where I live. They had been washed up for a few hours and because of this had practically ‘dissolved’ into the sand they stuck on. They dry out incredibly quickly because the jellies are made up of 95 – 98% water!