ANOMALOCARIS GRASPING APPENDAGE
A rare specimen from Chenjiang, China

My favorite!
Anomalocarids were at the top of the
food chain around 490-545 million years ago.
This one is depicted chomping down
with its circular jaw on a trilobite.

Alas, it's nearly impossible to get an
entire fossil of one of these beauties.
They wind up in museum vaults,
never to be seen by the public!

Here's an excellent link about it:
http://www.trilobites.info/anohome.html

This beautiful Illustration is from cambrico.galeon.com.