Chrysochromulina microcylindra is a species of marine haptophyte microalga in the genus Chrysochromulina, family Chrysochromulinaceae, class Prymnesiophyceae. The specific epithet microcylindra — small cylinder — refers to a minute cylindrical component of the scale structure on the cell surface, contrasting with the larger cylindrical scales of C. megacylindra and the shorter cylinders of C. brachycylindra. Together these three species illustrate the morphological continuum in scale cylinder dimensions within Chrysochromulina, and their differentiation highlights the role of quantitative ultrastructural measurements in haptophyte taxonomy. C. microcylindra has been recorded from Norwegian coastal marine environments and from Norwegian and Swedish waters more broadly, consistent with the established concentration of Chrysochromulina species diversity in Scandinavian coastal seas. These habitats are characterized by cold temperatures, high seasonal productivity driven by spring mixing of nutrient-rich deep water, and complex fjordic geomorphology that promotes diverse microhabitat niches for planktonic microalgae. The species is a nanoplankton organism engaged in photosynthesis using the typical prymnesiophyte pigment suite of chlorophylls a and c plus fucoxanthin. As with other genus members, mixotrophic capability is likely, allowing supplementary nutrition through phagocytosis of bacterial cells. C. microcylindra has not been evaluated under IUCN criteria and is listed as Not Evaluated. It represents one facet of the remarkable species richness that has emerged from systematic electron microscopy surveys of northern Atlantic nanoplankton.