The Wonderful World of Jellyfish


Sep 19, 2014 by British Blog

The jellyfish is a little known and much misunderstood creature: but what sort of creature? Well, officially jellyfish are inappropriately named, because they are definitely not fish, but rather invertebrate, free-swimming marine animals (they are also sometimes defined as plankton).

Living quite happily without a respiratory system, skeleton or heart, they are found in the waters of virtually all areas of the world, including the UK.

Jellyfish are ancient animals, having been around for more than 600 million years - that makes them older than the dinosaurs, and sharks.

Read on for some more fascinating facts about them - and prepare to be amazed!

  • Not all jellyfish sting or are toxic; the ones that do sting are categorised under the group name medusae. However, when jellyfish are toxic, they can be very toxic indeed: box jellyfish venom is the most deadly in the animal kingdom, and has killed more than 5,500 people since the 1950s.
  • There are several types of jellyfish: medusae (which sting), comb jellies/ctenophores (which do not sting) and salp.
  • A group of jellyfish is called a smack, swarm or bloom.
  • Most jellyfish live for less than a year, some for just a few hours. However, the aptly named immortal jellyfish can 'age' backwards: when faced with a potentially life-threatening crisis, its cells can revert to their earliest form, a polyp. This means that the immortal jellyfish is, theoretically, actually immortal.
  • Jellyfish are symmetrical, and most of them are transparent.
  • Jellyfish skin is so thin it absorbs oxygen through diffusion, so the animal does not need a respiratory system. Some jellyfish, however, do have rudimentary eyes. None of them have hearts or bones.
  • Jellyfish can be tiny (less than a centimetre) or massive. The longest jellyfish on record measured 160 feet, and the tentacles of the huge lion's mane jellyfish regularly grow to more than 90 feet.
  • However, even tiny jellyfish are not to be messed with. The Irukandji jellyfish is less than a centimetre in size, but its venom is 1,000 times more toxic than that of a tarantula.
  • Jellyfish eat phytoplankton, fish eggs and larvae, the young of many sea creatures and - sometimes - each other. Some even hunt medium sized fish and crustaceans, while others simply absorb food matter through their epidermis. Jellyfish are voracious eaters and can consume up to ten times their own bodyweight in food.
  • Large fish and turtles in turn eat jellyfish. Human consumption of jellyfish has been known, their tentacles are considered a particular delicacy in some parts of the world.
  • Jellyfish are more than 95% water.
  • Jellyfish are found in both oceans and in fresh water.
  • In November 2009, a net of huge jellyfish capsized a Japanese trawler. They have also been known to clog up the cooling systems of nuclear power plants.
  • The ox jellyfish swims at a speed of 21 feet per minute.
  • Scientists are currently worried about the sheer volume of jellyfish in the sea, and blame them for depleting the food stocks of other marine animals.