I understand you claim about the centipede (which does not necesaarily have 100 legs), but octopuses do have 8 legs. Nevertheless, there are thousands of species of centipedes/millipedes, with a total number of legs varying between 80 and 400 legs for common species (up to 200 for centipedes), so in some cases the term centipede can actually be correct. I suppose it is for the sake of convenience that we have not given different names to each species according to their exact number of legs !
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