Based on the direct examination of the fossil, which was uniquely preserved in a way that the exoskeleton could be viewed under a microscope to see the minute details, an artist has created this rendering of what Pentecopterus decorahensis actually looked like:
More amazing details are in the informative article from the Mirror, which you can find here.
Source: Mirror.co.uk – “Bizarre ancient sea scorpion measuring six feet long and lived 467 million years is discovered“