円口類
↑ Duméril, A.M. Constant (1806). Zoologie analytique, ou me ́thode naturelle de classification des animaux, Rendue plus facile a l'Aide de Tableaux Synoptiques. Paris: Allais
↑ Kuraku, Shigehiro, Ota, Kinya G., & Kuratani, Shigeru, S. Blair (2009b). “Jawless fishes (Cyclostomata)”. In S.B. Hedges & S. Kumar. Timetree of Life. oxford University Press. pp. 317–319. ISBN 978-0-19-953503-3
↑ Kuratani, Shigeru, & Ota, Kinya G. (2008.). “Hagfish (Cyclostomata, Vertebrata): searching for the ancestral developmental plan of vertebrates”. BioEssays 30 (2): 167–172. doi:10.1002/bies.20701. PMID 18197595.