Interesting Facts about Jellyfish

Quick Facts

  • Jellyfish are made up of an epidermis, gastrodermis and mesoglea. They do not have a central nervous system,a circulatory system, respiratory system, or a osmoregulatory system. They have an incomplete digestive system and therefore use the same orifice for intake of food and expulsion of waste materials.
  • The jellyfish don't have a brain or other sensory organs. They have small sensory organs called rhopalia on and around their bell. The rhopalia and nervous system help these fish to identify light and odor. The jellyfish use their 'nerve net' to detect the touch of another organism. This type of simple nervous system is found at the epidermis of these fish.
  • A group of jellyfish is called a 'smack'. They feed on small protozoa, large metazoa and other small fish in the sea. They generally trap these in their tentacles. Some of them do not have tentacles at all.
  • The male jellyfish releases its sperm into the water, which then travels to the mouth of the female jellyfish. This procedure allows for the fertilization of the ova. Most of these fish lodge the eggs in their oral armpits, forming a brood chamber for fertilization.
  • The tentacles of a jellyfish are an important defense mechanism. Each tentacle is covered with stinging cells, known as cnidocytes.
  • Jellyfish do not have any water motion, or are not hydrodynamic. This hampers their swimming speeds. It is necessary for them to create water currents which reaches their tentacles. They make this possible by opening and closing their bell shaped bodies in a rhythm.
  • Jellyfish swim by contracting and expanding their bodies. They do not have scales or shells. If exposed to the hot sun, they disappear, leaving only a circle of film.
  • Jellyfish have a defense mechanism of oral arms or tentacles which are covered with organelles called nematocysts. These nematocysts are paired with a capsule which contains a coiled filament that stings. The filament unwinds and launches into the target, thereby injecting toxins upon contact by foreign bodies.
  • Jellyfish are generally not dangerous to humankind. However, some can be very toxic, and cause deaths in humans. Recently, two deaths attributed to these fish were reported in Australia. A sting from these fish is extremely painful and can also cause various allergies in humans.
How jellyfish Work




  • The Box jellyfish has 64 anuses.
  • The Box jellyfish also has 24 eyes, but despite this, it can only see in a blurry fashion.
  • Jellyfish do not have a brain, respiratory system, circulatory system, or indeed an excretory system. Because of this, the jellyfish’s ‘mouth’ is also used for waste expulsion.

Did you know ...
... some jellyfish are bigger than a human and others are as small as a pinhead?
... people in some countries eat jellyfish?
... that jellyfish have been on Earth for millions of years, even before dinosaurs?
... jellyfish have no brain but some kinds have eyes?
... that jellyfish are mainly made up of water and protein?
... a group of jellyfish is called a smack?
What is a jellyfish?
The word jellyfish is a common term used to describe animals that are gelatinous or made up of ‘jelly-like’ material. There are many different types of jellyfish, including stinging kinds called medusae and non-stinging kinds called comb jellies or ctenophores. Another type of jelly animal called a salp is even in the same group as humans!

What is a bloom?
When huge numbers of plants or animals appear suddenly, scientists call it a 'bloom'. In some areas of the world, millions of jellyfish can swarm together, and these blooms cause problems for fisheries and tourism. If you've been at the beach or on a boat at some point when it seemed like jellyfish were everywhere – then maybe you have even seen a jellyfish bloom.

How do jellyfish blooms form?
Jellyfish are plankton (from the Greek word planktos, meaning to wander or drift) and are not strong swimmers, so they are at the mercy of the ocean currents. Blooms often form where two currents meet and if there is an onshore breeze thousands of jellyfish can be beached.

GOOD: Attack of the Giant Jellyfish!

Giant jellyfish

Exotic Jellyfish

Jellyfish Lake

Cuttlefish and Jellyfish


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