Paracatenula is a master of regeneration. Cut it in two, and both ends become fully functional animals. The back half will even re-grow a head and brain. “Chop them up and you can get ten,” says Gruber-Vodicka. “That’s probably what they do in nature. They get longer and longer, and then one end breaks off and there are two.” This skill depends entirely on the trophosome, the bacteria inside it, and the energy they lock away. As long as a fragment of flatworm contains enough symbionts, it can produce an entire animal. If the symbionts are too scarce, the fragment dies. Counter-intuitively,
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