Hemichordata (Acorn Worms and Pterobranchs)
- Photograph of an acorn worm (Saccoglossus kowalevskii).
- http://tolweb.org/tree?group=Hemichordata&contgroup=Metazoa

Introduction to the Hemichordata
- UCMP Berkeley's introduction to the acorn worms. The site includes information on graptolites.
- http://www.ucmp.berkeley.edu/chordata/hemichordata.html

Chordata introduction - Phylum Hemichordata
- A brief introduction to the hemichordates from the Biological Sciences at the University of Paisley.
- http://orion1.paisley.ac.uk/courses/Tatner/biomedia/units/chor5.htm