Well first, bogden is right "tortoise" is definitely not a six letter word. But bogden, "effigy" has been used before and also we are trying to stay away from words ending in "Y" because there aren't really any left. So I'm going to go back to K'lyn's post and pick a "T" word...

teleost - Of or belonging to the Teleostei or Teleostomi, a large group of fishes with bony skeletons, including most common fishes. The teleosts are distinct from the cartilaginous fishes such as sharks, rays, and skates.