Abstract
SYNOPSIS. Structure of the vegetative and asexually dividing forms of the large ciliate Climacostomum virens is redescribed with emphasis on stomatogenesis. These findings are discussed in relation to the taxonomic and possible evolutionary position of Climacostomum among heterotrichous ciliates. Comparative considerations of the buccal and somatic structures as well as of the stomatogenic patterns in this and other closely related ciliate genera indicate the need for placing Climacostomum and Fabrea in a new family, CLIMACOSTOMIDAE. The morphologic evidence suggests that Climacostomum may represent a line linking Fabrea and Stentor.