Includes radiolarians. These creatures are single-celled and have a shell composed of silica. Radiolarians are planktonic (floating in water) and often form a cone or sphere shape.

For more information:

http://www.ucmp.berkeley.edu/protista/radiolaria/rads.html

http://www.palaeos.com/Eukarya/Units/Rhizaria/Rhizaria.html#Radiolaria