Jellyfish

Jellyfish are cnidarians, related to sea anemones and sea slugs. They consist of a dome-shaped body and tentacles that trail behind them. Jellyfish are able to swim through the water by pulsing their jelly-like bodies. Their tentacles are covered in poisonous stinging cells called nematocysts. These tentacles can paralyze or kill fish. Some jellyfish, like the box jellyfish below, are powerful enough to kill humans. The venom in a box jellyfish can stop a person's heart in less than 3 minutes.

While most jellyfish are relatively small, some can grow to enormous sizes.

During certain times of year, jellyfish can be found in huge numbers, clouding the seas with their pulsating forms.

Some jellyfish can even glow in the dark.

Dinoflagellates: Bioluminescent Algae

In some oceans when the night is dark enough, you can see the waves glow as the water stirs. This is caused by phytoplankton called dinoflagellates. They give off a soft blue glow when disturbed. The chemicals they use are similar to the ones causing lightning bugs to glow.


When a person swims through the algae, the motion gives off a glow all around them, looking like angel's wings. Boats and wave action can also cause ripples of light to cascade in their wake. This video was taken at a dock in Australia where this algae is plentiful. People throw water on it to cause it to glow in amazing patterns.