Coccolithophores. Coloured scanning electron micrograph (SEM) of Gephyrocapsa. oceanica. This small algal organism (coccolithophore) is a calcareous phytoplankton and surrounded by a skeleton (coccosphere) composed of calcium carbonate plates (coccoliths). When the organism dies, the plates separate and sink to the ocean floor. Individual plates have been found in vast numbers and can make up the major component of a particular rock, such as the chalk of England. G. oceanica is found in marine environments world wide. Magnification: x1000 when printed at 10 centimetres wide