The Fog Worms are a species of giant, fog-dwelling, prehistoric worm that appeared on primeval episode 2.2 and 5.5. They had features of the priapulid predator worm Ottoia prolifica, i.e. an extensible proboscis with teeth. Their body looks rather like a sea cucumber. In the Cambrian, priapulid worms grew to much bigger size than nowaday though we don't have fossils of any the size shown in the show and they were 1 of the dominant predators.