Recently discovered, and very complex:

https://www.livescience.com/nightmare-creature-multitool-head.html?utm_source=ls-newsle...

"... have found dozens of fossils of this species in recent years that include preserved soft tissue of the mouthparts, along with the animals' multiple legs and bulbous eyes.

Comment: very early in the Cambrian and way more complex than anything in the Ediacaran, despite all efforts to imply the gap is not that large..

How is there 'preserved soft tissue' after 500 million years?