Metaspriggina walcotti Simonetta & Insom 1993
Middle Cambrian
Burgess Shale, Stephens Formation
Field British Columbia
British Columbia, Canada.

Think of it as one of the very earliest fish. Discovered by Walcott himself, but not described until decades after his death, Metaspriggina possessed a flexible notochord, segmented muscles, large eyes, and a series of paired cartilaginous structures that are thought to represent some of the earliest precursors to vertebrate gill supports. These features make it one of the most significant fossils for understanding the evolution of fishes and all backboned animals.
12mm on 70mm matrix. Not complete, but the only one we have ever even heard of for sale. Extremely rare.

See: Wikipedia – Metaspriggina

A comprehensive review paper on Metaspriggina can be found here: A primitive fish from the Cambrian of North America

Compare to our specimen of Nuucichthys, a brand new Cambrian fish/chordate similar to Metaspriggina that was first described only two years ago!:The Natural Canvas – Cambrian Chordate – Nuucichthys