Pterobranchia
Cephalodiscus and Classification of Cephalodiscoid, Cephalodiscus densus Andersson, 1907 (Hemichordata, Cephalodiscus gracilis, Cephalodiscus graptolitoides Dilly, 1993., Cephalodiscus lutetianus (Graptolithoidea, Cephalo, Class Pterobranchia, Classification of the Extant Hemichordata, Collagen in the pterobranch coenecium, Pterobranchia: Classification of the Rhabdopleuroi, Rhabdopleura kozlowskii
Chordata introduction - Phylum Hemichordata
A brief introduction to the hemichordates from the Biological Sciences at the University of Paisley.
Hemichordata (Acorn Worms and Pterobranchs)
Photograph of an acorn worm (Saccoglossus kowalevskii).
Introduction to the Hemichordata
UCMP Berkeley's introduction to the acorn worms. The site includes information on graptolites.