Threatened species of Hemichordata

Hemichordates form a small phylum (only a few hundred species). Their importance for the study of vertebrate evolution however cannot be underestimated. The name "hemichordate" means "half chordate" and hemichordates share some (but not all) of the typical chordate characteristics. Of the three classes of hemichordates, the most familiar of those living are the Enteropneusta, the acorn worms. Some of these worms may be very large; one species may reach a length of 2.5 meters.