DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Portuguese Man O' War (Physalia utriculus). Despite its jellyfish appearance the Man-o-War is not a true jellyfish but a siphonophore. It differs from a true jellyfish in that it is not actually a single creature, but a colonial organism (hydrozoan) made up of many minute individuals called zooids. It lives near the ocean surface and floats with a sail-like bladder. It commonly occurs in the Pacific Ocean and is often seen in warmer waters around the Hawaiian Islands and Australia. Physalia utriculus feeds on small fish and other small marine plankton such as copepods and shrimp. They surround their prey with their tentacles that contain stinging cells called nematocysts. The nematocysts eject a long tubule (with barbed hooks) into the prey simultaneously releasing a poison (venom) that paralyzes it before being consumed. Its larger relative, Physalia physalis, can have a body size up to 2 feet and tentacles over 150 feet long.
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