• single-celled animals (“protista”), like forams but with a siliceous shell
• geologic range: Precambrian – Recent
• a planktonic mode of life, in fully marine settings
• biostratigraphically significant in particular areas/intervals but subordinate to other fossil groups and therefore has relatively few practicing specialists
• can be significant in sediments deposited below the CCCD

Left: Assorted radiolaria; some of the most beautiful microorganisms in the oceans. Right: The living radiolarian is very similar to the planktonic foram.