The hemichordates form a small phylum of a few hundred species. They are worm-like creatures with their bodies divided into 3 parts, a pre-oral lobe, a collar and a trunk. Their name means “half chordate” and they have certain primitive features that resemble those of true chordates. The three main groups are the Enteropneusta, or acorn worms, the Pterobranchia and the Graptolithina.