Can't live without this one:
THE CENTIPEDE:
"The word centipede means “hundred feet,” but there are no centipede species that have exactly 100 legs. Depending on the species, they may have as few as 30 and as many as 354 when mature."
(information from terro.com, in article "All About Centipedes".)
Disclaimer - this Ent has not personally viewed and studied all species of centipedes, so can neither confirm, nor deny, there is no species having exactly 100 legs.
Ent Note - however, as the centipede grows, it has 2 legs per body segment. So though 'no centipede species has exactly 100 legs', every centipede living long enough to attain 50 body segments will, for that period of time, have 100 legs.