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They live in symbiosis with the chemosynthetic bacteria that provide the worms with their nutrition. It took the scientific specialists awhile to understand the functioning of the animal, which at first they believed to be a filter feeder.
At first they were described as having no eyes, no mouth, or any other obvious organs for ingesting food or secreting waste, and no means of locomotion. It was not a worm, a snake, nor an eel, but it wasn't a plant either.