Pikaia, prints of which are found in shales - it could be yet to larvae, which rolled a landslide. And the adult could be much larger and more complex.

http://translate.google.com/translate?hl=ru&sl=ru&tl=en&u=http%3A%2F%2Fspacenoology.agro.name%2F%3Fpage_id%3D82

And it gives great scope for imagination:

http://translate.google.ru/translate?js=y&prev=_t&hl=ru&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Fspacenoology.agro.name%2F%3Fpage_id%3D329&sl=ru&tl=en&swap=1