Multimedia Gallery
Jellyfish Anatomy
Illustration showing the anatomy of "true" jellyfish (class Scyphozoa).
Jellyfish are the simplest swimming animals on Earth. They are composed of about 95 percent water. (By contrast, humans are about 65 percent water.) The high water content of jellyfish explains why they immediately collapse into defeated, deflated blobs when removed from water. With few exceptions, jellyfish are brainless, bloodless, boneless and heartless, and have only the most elementary nervous systems. So simple, each jellyfish is but a few evolutionary steps beyond being just a stinging bladder of sea water.
In fact, jellyfish are so at one with water that they are barely distinguishable from their marine habitats via sophisticated, acoustic surveys. Whats more, the transparent, ghost-like bodies of jellyfish provide excellent camouflage, enabling jellyfish to hide in plain sight from most prey species, and thereby surprise them.
The simplicity of jellyfish and their resulting simpatico with the sea helps explain the adaptability of jellyfish, which have survived on Earth for over 500 million years. Moreover, the ability of these most simple creatures to dominate and essentially rule many diverse ecosystems testifies to the potential power of the lowest common denominator.
To learn more about the basics of jellyfish biology, what scientists have learned thus far about the worldwide increase in jellyfish populations, and the causes of jellyfish swarms and how they affect both human and marine life, see the NSF Special Report, "Jellyfish Gone Wild!" (Date of Image: 2008)
Credit: Zina Deretsky, National Science Foundation
Images and other media in the National Science Foundation Multimedia Gallery are available for use in print and electronic material by NSF employees, members of the media, university staff, teachers and the general public. All media in the gallery are intended for personal, educational and nonprofit/non-commercial use only.
Images credited to the National Science Foundation, a federal agency, are in the public domain. The images were created by employees of the United States Government as part of their official duties or prepared by contractors as "works for hire" for NSF. You may freely use NSF-credited images and, at your discretion, credit NSF with a "Courtesy: National Science Foundation" notation.
Additional information about general usage can be found in Conditions.
Also Available:
Download the high-resolution JPG version of the image. (1 MB)
Use your mouse to right-click (Mac users may need to Ctrl-click) the link above and choose the option that will save the file or target to your computer.