Peridinium is a genus of motile, marine and freshwater dinoflagellates.[2][3] Their morphology is considered typical of the armoured dinoflagellates, and their form is commonly used in diagrams of a dinoflagellate’s structure.[4][2] Peridinium can range from 30-70 μm in diameter, and has very thick thecal plates.[4][2]\
(From: Wikipedia, July 2015)