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Jellyfish Gone Wild — Home
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Jellyfish Gone Wild — Text-only | Flash Special Report
Anatomy

JELLYFISH ANATOMY: A BELL WITH FEW WHISTLES

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.

What’s 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.

Illustration Credit: Zina Deretsky, National Science Foundation