giant clam

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hydrothermal vent A place on the ocean floor, on or adjacent to a mid-ocean ridge, from which there issues water that has been heated by contact with molten rock, commonly to about 300°C. The vent water often contains dissolved sulphides. These are oxidized by chemosynthetic bacteria, which fix carbon dioxide and synthesize organic compounds. Near the vents, at temperatures up to 40°C, there are highly productive communities comprising animals that utilize the organic compounds or live symbiotically with the chemosynthetic bacteria; these organisms support carnivores and detritivores. These communities include beard worms (phylum Pogonophora) that completely lack a digestive tract, Munidopsis crabs (superfamily Galatheoidea), giant clams (e.g. Calyptogena magnifica), mussels, acorn worms (class Enteropneusta), and many more. Vent fluids containing high concentrations of iron, manganese, and copper tend to be hot (about 350°C) and black. They are known as ‘black smokers’. ‘White smokers’ flow more slowly, are cooler, and contain high concentrations of arsenic and zinc. See HYDROTHERMAL ACTIVITY, and HYDROTHERMAL MINERAL. See also COLD SEEP.