Light micrograph of an Acantharian, Acanthoplegma sp., an amoeboid protozoan found in marine plankton. The Acantharians form a sub-order of the Radiolarians. They have an intricate and complex internal skeleton said to be composed of spicules of strontium sulphate. Around this is an external layer of highly vacuolated buoyant protoplasm, from which radiate numerous pseudopodia. Magnification unknown.