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A white wave shape.

Jellies

Learn more about these ancient drifters of the sea!

Jellies have been around for hundreds of millions of years—since before dinosaurs roamed the Earth. They’re members of the phylum cnidaria, pronounced NYE-daria, from the Greek word for “stinging nettle.” Members of this group of invertebrates, meaning animals without backbones, have stinging capsules in the tentacles surrounding their mouths.

There are over 2,000 known jelly species worldwide, and scientists believe many more remain to be discovered. Here at the Aquarium, we have three jelly species in our care: moon jellies, commonly found in cooler, temperate waters like those of the Salish Sea; and two species found in the warmer, tropical waters of the Indo-Pacific—spotted lagoon jellies and upside-down jellies.

At the Aquarium

A big, fascinating family

Jellies are related to a lot of interesting creatures, many of which can also be found at the Seattle Aquarium: sea anemones, sea pens, sea fans, sea whips, and soft and stony corals, to name just a few.

Jellies are plankton, really?

Many people think of plankton as microscopic creatures but they’re actually defined by their inability to swim against the current: they’re drifters and floaters. While jellies can pulsate their bells to move, the force isn’t strong enough to propel them against the current. So not only are jellies plankton, they’re the very largest form of plankton on Earth.

A mirror image

Another fascinating fact: jellies have what’s called radial symmetry. That means that if a jelly was divided through the center and across the bell in any direction, the two halves would be exactly the same.

You can make a difference for jellies everywhere

It starts with small, everyday choices. For example, using reef-safe sunscreen helps prevent damage to delicate marine ecosystems where jellies and other marine animals make their homes. And reducing use of fertilizers and pesticides helps keep chemicals out of the ocean. Interested in more ideas? Visit our Act for the Ocean webpage!

Quick facts

Jellies have been around since before dinosaurs roamed the Earth!

Jellies are the largest form of plankton.

These invertebrates have stinging capsules in the tentacles surrounding their mouths.

Explore More Invertebrates