Jellyfish

Animal of Contrasts

The most popular jellyfish are members of the class Scyphozoa (true jellyfish), from the Greek word skyphos—a kind of drinking cup—alluding to the cup (bell or umbrella) shape of their bodies with trailing stinging tentacles. This form is also called ‘medusa’—from the gorgon of legend.

There is another kind of jellyfish called hydrozoan jellyfish. They are smaller than true jellyfish and have the velum, a circular membrane under the umbrella with which the hydrozoan jellyfish use to propel themselves through the water. True jellyfish propel themselves by alternately contracting and relaxing a ring of muscles around the rim of their domes.

Most jellyfish live in oceans but some are found in fresh waters (these are usually the small, unremarkably colored ones).

Among the animals, the jellyfish is probably the one with the most contrasts. For one, they may be familiar to us, yet they also lead secret lives.

The Secret Life of Jellyfish

We are most familiar with the umbrella-shaped jellyfish, yet we seldom know that many of them spend part of their lives rooted plantlike at the bottom of seas and rivers. This is called the polyps phase. Looking like individual sea anemones, polyps are longer-lived than the medusa form. They sometimes bud off, producing more polyps. In some (typically warm) seasons, polyps constrict several times across their bodies, producing stacks of shallow cups which detach, forming the familiar medusa form of the jellyfish.

While their bodies may be simple, a British scientist thinks aliens in gas planets would resemble gigantic jellyfish.

Animal of Many Roles

Jellyfish also play a lot of sometimes contrasting roles:

• They are among the smallest sea animals, yet some jellyfish take the title of among the largest sea creatures including the Lion’s Mane Jellyfish.
• They inhabit the shallowest seas, yet some jellyfish are found even in the sunless depths of the sea—like the blood red jellyfish and the giant Stygiomedusa gigantea, named after the hellish blackness of legendary River Styx.
• They are harvested as an important delicacy in some parts of the world, yet some species, like the Nomura’s Jellyfish, interfere with fishing in parts of Japan and China.
• Some jellyfish are colorful and harmless—one of the most fantastic tourist attractions of Palau is snorkeling among swarms of Golden Jellyfish at Jellyfish Lake. In contrast, one of the most agonizing (and deadly) experiences a man can have is to be stung by the nearly invisible Box Jellyfish, probably the most venomous animal in the world.

Other Jellyfish facts:

• Jellyfish can contain as much as 99% water.
• Jellyfish are among the oldest multi-organ animals in the world—they have been on earth at least 500 to 700 million years ago.
• The ‘Immortal Jellyfish’ (Turritopsis nutricula) can virtually live forever by having its jellyfish form change back to the polyps form, which create more jellyfish, which can change back to polyp form (repeating the cycle).
• Some jellyfish don’t need to catch prey. They live with symbiotic algae in their bodies that manufacture food for them. They just need to be well exposed to sunlight.

Since most jellyfish live in moving sea water, they were mostly kept by well funded public aquaria in specialized large viewing tanks. However, a San Francisco company, Jellyfish Art, has started selling desktop jellyfish tanks for the home. Now you can have your very own jellyfish pets.