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The Siphonophorae are a group of marine animals closely related to jellyfish and corals. Like jellyfish, siphonophores are free to move around the ocean. They hunt and capture fish and crustaceans by means of stinging tentacles. However, like adult coral, siphonophores are colony animals. A single siphonophore consists of multiple living animals–some of which are quite different from each other, since they serve different functions in the overall colony. Their unusual nature makes them a focus of the scientific (and philosophical) question of what constitutes an individual organism as opposed to a group of organisms.
The best known siphonophore, the fearsome Portuguese man-of-war, possesses a gas filled bladder from which long colonies of stinging animals hang. Most siphonophores however are not found near the surface. Siphonophore colonies form delicate chains which can be quite long. Some have been recorded to be 130 feet or more in length—substantially longer than the mighty blue whale. Additionally some siphonophores are bioluminescent.
Marine biologists are beginning to think that siphonophores are more prevalent and important than initially believed. Scientists once used nets and tows to capture specimens and calculate overall biomass. These methods broke delicate siphonophores into unidentifiable pieces. Now that biologists are using unmanned submarines to study the ocean, they have been finding many more siphonophores than they expected.