Most diatoms floating in marine plankton are centric diatoms, with cells that are radially symmetrical. Top view of Coscinodiscus concinnus, the largest species of this genus in the North sea. It can be almost half a millimetre (450 micron) in diameter.

See a side view of a different species of Coscinodiscus.

Part of the Collection of the Diatom Display of the Micropolitan Museum © Wim van Egmond