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

Examples of radiolarian in a Sentence

Recent Examples on the Web At left, a large Thalassicolanucleata radiolarian with a central capsule enclosing the nucleus. Discover Magazine, 3 June 2015 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 examples are programmatically compiled from various online sources to illustrate current usage of the word 'radiolarian.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1869, in the meaning defined above

Time Traveler
The first known use of radiolarian was in 1869

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Cite this Entry

“Radiolarian.” Dictionary, Merriam-Webster, Accessed 24 Jul. 2024.

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

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