Phyllocarids are strange, large, shrimp-like creatures that are a sub-class of crustaceans. Due to their fragile exoskeletons, complete articulated examples are rare. Echinocaris is found in the same lenses as Greenops widderensis, Tornoceras and Dolorthroceras. Phyllocarid mandibles are found on their own (albeit rarely) and not articulated to the body.
 
Echinocaris punctata
Widder fm, Hamilton group
Arkona, Ontario, Canada
Middle Devonian (Givetian)