Cassiopea jellyfish make stinging water

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Jellyfish are odd animals. They float around in the ocean with no brain, bones, blood or heart. They have arms, called tentacles, which contain cells that sting or stun prey that they can eat.

One type of jellyfish, the Cassiopea, must have become tired of floating because it lives on the bottom of the ocean. It is found in shallow water in places like southern Florida and Hawaii. Known as the upside-down jellyfish, it sits on the sand, its tentacles pointed upward. It looks kind of like a flower and can get as big as a Frisbee.

People swimming above the upside-down jellyfish sometimes complained their skin itched or stung. The swimmers called it stinging water.

“We knew that the water gets stingy, but no one had spent the time to figure out exactly how it happens,” said zoologist Allen Collins of the National Oceanic and Atmospheric Administration.

So Collins and other scientists did some studies. They found that when Cassiopea jellyfish are disturbed or feeding they will release snot-like blobs filled with stinging cells.

These stinging cells are called nematocytes. The snot blob also had some cells with waving hairs that helped move the stinging cells through the water.

The jellyfish usually eat algae that live on the creatures. Scientists think the upside-down jellyfish releases the blobs to kill small creatures like shrimp to eat when they are not getting enough algae.

The jellyfish gets its name, Cassiopea, from a Greek myth. Cassiopea was once a queen who bragged about how beautiful she was. For being so proud she was punished by the sea god Poseidon who tied her to a chair in the heavens. That chair in the heavens is a constellation of five stars in the northern sky, which are also called Cassiopea.

— Brett French,

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