Lenz, Alfred C., et al. “Part V, Hemichordata, 2nd Revision, Chapter 5, P. 387-571: Enteropneusta, Pterobranchia (Graptolithina)”. Treatise on Invertebrate Paleontology, Jan. 2023, pp. 387–571, https://doi.org/10.17161/tip.vi.25191.