Esteban, Genoveva F.; Bradley, Mark W.; Finlay, Bland J. (2009). A case-building Spirostomum (Ciliophora, Heterotrichida) with zoochlorellae. European Journal of Protistology. 45 (2): 156—8. doi:10.1016/j.ejop.2009.01.002. PMID19264465.
Esteban, Genoveva F.; Bradley, Mark W.; Finlay, Bland J. (2009). A case-building Spirostomum (Ciliophora, Heterotrichida) with zoochlorellae. European Journal of Protistology. 45 (2): 156—8. doi:10.1016/j.ejop.2009.01.002. PMID19264465.