Ultrastructure of Calyptrosphaera radiata, sp. nov. (Prymnesiophyceae, Haptophyta)

A novel member of the Calyptrosphaeraceae surrounded by a hyaline sheath, with only one chloroplast and without an emergent haptonema, is tentatively described as a species of Calyptrosphaera Lohmann. It has an interrupted body to its single pyrenoid and a unique microtubular root complement with only one crystalline root (CR) nucleating on root 2 (R2). At preprophase it produces a CR1, lending support to the idea that these crystalline roots contribute to the mitotic spindle. It shares numerous ultrastructural traits with the heterococcolithophorid Cruciplacolithus neohelis but, although it is tempting to consider it a haploid phase of this organism, is distinct from it.