ra·​di·​o·​lar·​i·​an ˌrā-dē-ō-ˈler-ē-ən How to pronounce radiolarian (audio)
: any of three classes (Acantharia, Polycystina, and Phaeodaria) of usually spherical chiefly planktonic marine protozoans having radiating threadlike pseudopodia and often a siliceous skeleton of spicules
radiolarian adjective

Illustration of radiolarian

Illustration of radiolarian

Example Sentences

Recent Examples on the Web The organic carbon decline coincided with the disappearance of more than 50 species of radiolarians, which served as a food source for numerous marine species and whose disappearance was an indicator of a major biological crisis. Reuters, WIRED, 10 May 2001

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'radiolarian.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History

First Known Use

1869, in the meaning defined above

Time Traveler
The first known use of radiolarian was in 1869

Dictionary Entries Near radiolarian

Cite this Entry

“Radiolarian.” Dictionary, Merriam-Webster, Accessed 29 Jan. 2023.

Kids Definition


ra·​di·​o·​lar·​i·​an ˌrād-ē-ō-ˈlar-ē-ən How to pronounce radiolarian (audio)
: any of various usually ball-shaped marine protozoans that have small spines radiating from the shell and have a skeleton containing silica

More from Merriam-Webster on radiolarian

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

The Great British Vocabulary Quiz

  • union jack speech bubble
  • Named after Sir Robert Peel, what are British police called?
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Solve today's spelling word game by finding as many words as you can with using just 7 letters. Longer words score more points.

Can you make 12 words with 7 letters?