Anatomy of a Jellyfish

by AMNH on

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Jellies come in many shapes, sizes, and colors. Even so, true jellyfish (from the phylum Cnidaria) share a few key traits in common. The first is their umbrella-like body, known as a “bell.”

Jellyfish with a spotted, mushroom-shaped bell and dangling tentacles makes its way through the sea.
The white-spotted jellyfish gets its name from the marks adorning its bell.
Courtesy of N. Hobgood/Wikimedia Commons

Hanging from that bell, you can see the long, thin tentacles of the jelly fish. These body parts are often lined with structures known as nematocysts, which deliver the jelly’s signature sting.

Saucer-like moon jellyfish floats along undersea, with other moon jellyfish in the background.
The bell of the moon jellyfish is ringed with many fine tentacles.
Courtesy of A. Vasenin/Wikimedia Commons

Among their many tentacles, some jellyfish have parts known as oral arms. These long appendages move captured prey to the animal’s mouth, which is usually found on the underside of the bell. Some species have even ditched a mouth entirely. These jellies ingest food directly through openings in their oral arms.

Jellyfish trailing long, frilly, dangling tentacles dives deeper underwater.
The frilly oral arms of this sea nettle jelly are on display above. 
Courtesy K. Edblom/Flickr

To learn more about jellies—and experience life in their underwater world—visit The Jelly Dome through June 30 in the Milstein Hall of Ocean Life.