Morphological development of Pleurochyrsis carterae coccoliths examined by cryo-electron tomography.

•Forming coccoliths of Pleurochrysis carterae were extracted from within the cell.•Cryo-electron tomography was used to characterize forming coccoliths.•Three stages of coccolith development were recorded and reconstructed in 3D.•Crystal competition proposed as a mechanism in shaping coccolith crystals.