Ottoia.

Ottoia was a strange priapulid worm that lived in tunnels and then ambushed its prey. 

Ottoia stuck a weird appendage out of its head to grab prey and pull it into its hole. 

The image below includes Diaphora, an ancient bivalve, Yohoia, a relative of a shrimp, the shed skin of an Anomalocaris pincer, Leanchoilia, and Ottoia. Ottoia ate small trilobites, and hyolithids like Haplophrentis. Opabinia was one of its predators.