Pikaia gracilens is one of the most primitive chordates known. It lived in the Middle Cambrian, about 505 million years ago, and was first discovered, and described, in the famous Burgess Shale in Canada by Charles Walcott. 
Pikaia's anatomy confirmes its taxonomic position among the chordates. It was a compressed, leaf-shaped animal with an expanded tail fin; the flattened body is divided into pairs of segmented muscle blocks, seen as faint vertical lines. The head appears to be small and bilobate with no obvious eyes.
 
This model is the most detailed model you can find on the web, with a resolution of less than 25 microns, it is made entirely out of resin and it is scientifically correct.