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How do jellyfish swim?

Jellyfish float on ocean currents, but they also swim in a couple of different ways. This post has two videos showing how jellyfish swim.

If you’ve ever seen a jellyfish in the ocean, you know they float on ocean currents. But jellyfish can also swim by a couple of different mechanisms, as shown in the videos below.

Contrary to what you might think, the familiar long tentacles of a jellyfish aren’t involved in swimming. Instead, those tentacles contain the jelly’s stinging cells. Plus the jelly can pull up its tentacles to feed on captured prey.

Most jellies use a form of jet propulsion to move through seawater. The video below, from Monterey Bay Aquarium, illustrates.

What’s happening here? You might understand it better if you cup your hand, as if you were about to pick up a ball. Now close your fingers. The air space inside your cupped palm just got smaller. This is what most jellyfish do. They squeeze their bodies in order to push jets of water from the bottom of their bodies to propel the jellyfish forward.

One jellyfish – called a comb jellyfish – has another way of swimming. It has tiny, transparent, hair-like cilia that beat continuously as a form of propulsion, so that the comb jelly rows through the water. In the video below – from Monterey Bay Aquarium – you can see a bloodybelly comb jelly as it swims.

The sparkling display from the comb jelly’s cilia happens because incoming light is diffracted, or dispersed. In the deep sea, where no light is shining on the jelly, the red-colored comb jellyfish is nearly invisible, because red creatures in the ocean blend into the dark background.

Jellyfish are related to sea anemones and coral. These creatures use special stinging cells on their tentacles – as jellyfish do – to capture prey. But, unlike jellies, sea anemones and coral are rooted to one spot in the ocean, while jellyfish float on ocean currents – or swim. Different jellies swim in different ways. Jellies are graceful sea creatures – wonderful to watch. Just watch out for the stingers!

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