Megacheira

Megacheira ("great hands") is an extinct class of predatory arthropods. They had a pair of short enlarged appendages at the front. They look like early chelicerates. 
Most of them lived in marine environments round the world from the lower to middle Cambrian. It looks like they were quite common then. However, one perfectly preserved specimen of "Enalikter" was found in the Silurian of Herefordshire (England). Another species ("Bundenbachiellus") was found in the early Devonian of Germany.