These arachnids, belonging to the arthropod phylum, have been given this name because their structure is reminiscent of scorpions. However, their anatomical characteristics are much closer to those of spiders than of scorpions. The oldest known specimens lived in the Devonian period (417 to 354 million years ago). And these invertebrates have never changed since the moment they first appeared in the fossil record. The fact that they remained unchanged for hundreds of millions of years is proof that they never evolved.