Jellyfish are amongst the most beautiful and mesmerizing creatures of the marine world. They inhabit all the oceans and exist at every layer from the surface to the very depths of the water. There are more than 1500 known species of jellyfish in the world with new ones being discovered with alarming regularity. Jellyfish have existed for more than 650 million years, since ever before dinosaurs existed! They have survived changing climate conditions over centuries and are expected to continue to do so. They are, in fact, called the 'cockroaches of the water world' for their ability to survive damaged environments.

Jellyfish are members of the phylum Cnidaria. While some members of this phylum are stationary like sea anemones, sea whips and coral, jellyfish are free-swimming. They do not possess a brain or specialized systems for any bodily function like circulation, digestion, reproduction, etc. They only have an elementary nervous system in which the nerve receptacles themselves are responsible for sensing and reacting to external stimuli. Their bodies are centrally symmetrical, consist of a bell and flowing tentacles and oral arms near the mouth. The mouth is just a small cavity containing the gullet and intestines, with the anus on the other end. The tentacles and oral arms help pushing the food in the mouth. The tentacles of a jellyfish contain numerous nematocyst which carry the venom and cause the sting.

The size and color of jellyfish differ from species to species. While some species are almost transparent, some species have vivid colors like red, purple, blue and pink. While some jellyfish are only a few centimeters wide and have no tentacles, the largest know species of jellyfish can grow up to 8 feet wide with tentacles of more than 120 feet in length.

Even though jellyfish have been abundant in nature, they have been extremely difficult to study because of their inherent fragility. Did you know that only 5% of a jellyfish's body mass is made of solid organic matter? They are easily injured and killed in the process of netting them. Also, they are very difficult to keep in a regular aquarium. They are prone to injuring themselves if they touch the inside walls of the aquarium and they also tend to get stuck in corners and die. The free waters of the ocean are the only places where jellyfish can thrive.

Until recently, only public aquariums and professional aquarists could set up complex and sophisticated aquariums to keep jellyfish captive. In the last few years, there have been huge developments in the technology and advanced designs of jellyfish aquariums are making it possible for hobbyists to keep and breed jellyfish in their homes.

Despite their sensational appearance in books and films, most species of jellyfish are completely harmless to humans. Their venom has no more effect on human than mild discomfort. However, there are a few species of jellyfish that can cause harm to humans. These include lion's mane, box jellyfish, Portuguese man-of-war and Irukandji. Depending on the species of the jellyfish and the victim, some jellyfish can also prove to be fatal.
Normen FAdel
Author of the article
writer and blogger, founder of jellyfish .

New of label : Jellyfish Adaptations and Abilities

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