a membrane, but are in direct contact with the host's cytoplasm; however, other observers have noted the presence of perialgal vacuoles around the algae. Classification The species Climacostomum virens was first described in 1833 by Christian Gottfried Ehrenberg, under the name Spirostomum virens. In 1859, Samuel Friedrich von Stein moved Spirostomum virens to a new genus, which he called Climacostomum. In his Manual of Infusoria (1880), William Saville-Kent rejected Stein's genus, assigning the species instead to Leucophrys patula, which he described as synonymous with Ehrenberg's Spirostomum virens and Leucophrys patula, as well as the Trichoda patula of O.F. Muller. However, the genus was retained by other researchers, including Alfred Kahl. In a detailed study of its physical characteristics, published in 1972, Arthur J. Repak placed Climacostomum with the genus Fabrea in a new family he named Climacostomidae.Recently, molecular analyses have shown that, while the Heterotrichea as a whole are a monophyletic group, the taxon Climacostomidae is paraphyletic, the genus Fabrea being more closely related to the ciliates Eufolliculina and Maristentor than to Climacostomum. Among the other Heterotrichs, Climacostomum appears to be most closely related to Chattonidium and Condylostoma''. Video gallery References Ciliate genera Heterotrichea Articles containing video clips