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

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