The flower-hat jellyfish

1. Jellyfish first appeared about 650 million years ago and are found in every ocean, from the surface to the deep sea. Some are also found in fresh water

2. Medusa (plural medusae) is another word for jellyfish. Medusa is also the word for jellyfish in: Greek, Finnish, Portuguese, Romanian, Hebrew, Serbian, Croatian, Spanish, French, Italian, Hungarian, Polish, Czech, Slovak, Russian and Bulgarian

3. Since jellyfish are not actually fish, some people consider the term jellyfish a misnomer, and American public aquariums have popularized use of the terms jellies or sea jellies instead

Photograph by TRINKO

4. A group of jellyfish is called a bloom or swarm

Jellyfish Bloom – Photo by DAVID DOUBILET

5. Jellyfish do not have a respiratory system since their skin is thin enough that the body is oxygenated by diffusion

6. Jellyfish do not have a brain or central nervous system, but rather have a loose network of nerves, located in the epidermis, which is called a “nerve net.”

The Australian Spotted Jellyfish

7. Jellyfish are composed of more than 90% water. Most of their umbrella mass is a gelatinous material (the jelly) called mesoglea, which is surrounded by two layers of cells which forms the umbrella (top surface). The subumbrella (bottom surface) of the body is known as the bell

Nomura Jellyfish (Yomiuri Shimbun/AFP/Getty Images)

8. Jellyfish are dioecious; that is, they are either male or female. In most cases, to reproduce, both males and females release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms

9. Box jellyfish venom is the most deadly in the animal kingdon and has caused at least 5,568 recorded deaths since 1954. Each tentacle has about 500,000 sindasites which are harpoon shaped needles that inject venom into the victim

10. The lion’s mane jellyfish is the largest known species of jellyfish. The Arctic Lion’s mane jellyfish is one of the longest known animals and the largest recorded specimen had a bell (body) with a diameter of 2.3 m (7 feet 6 inches) and the tentacles reached 36.5 m (120 feet). It was found washed up on the shore of Massachusetts Bay in 1870

Sources

– http://en.wikipedia.org/wiki/Jellyfish

– http://en.wikipedia.org/wiki/Box_jellyfish

– http://en.wikipedia.org/wiki/Lion%27s_mane_jellyfish

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