Two things: first, horseshoe crabs almost certainly have changed/evolved considerably over four hundred million years, just in aspects of their physiology that aren’t fossilized. Second, horseshoe crabs have like nine different types of eyes; even that tail is essentially one big eye, covered in photoreceptive cells. We humans consider ourselves the “dominant” species, but I don’t think we could handle crawling around in slime and mud for four hundred million years quite as well as they have.
Two things: first, horseshoe crabs almost certainly have changed/evolved considerably over four hundred million years, just in aspects of their physiology that aren’t fossilized. Second, horseshoe crabs have like nine different types of eyes; even that tail is essentially one big eye, covered in photoreceptive cells. We humans consider ourselves the “dominant” species, but I don’t think we could handle crawling around in slime and mud for four hundred million years quite as well as they have.