What are Radiolarians?

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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 19 January 2020
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Radiolarians are microorganisms in the order Radiolaria. They are most commonly found in the ocean, where they drift with the currents at all depths and all over the world, with some biologists suspecting that there may be freshwater species as well, although this has not been confirmed. From a scientific point of view, radiolarians are especially interesting to study because they evolve very rapidly, creating a sprawling family tree which can be used to establish the history of other organisms alongside the radiolarians.

Several features make these protozoans distinctive. The first is their silicate skeletons, which often form into complex patterns which cause them to resemble delicately blown glass. Numerous researchers have commented on the elegant beauty of radiolarians, and some very fine examples are often on display in the photography collections of people who study these interesting creatures. Historically, radiolarians were a topic of intense interest to scientists as they explored the technology of the microscope.

Most radiolarians exhibit radial symmetry, which explains their name, and this symmetry is often marked with pseudopods, false feet which jut out from the body of the organism. These false feet help radiolarians to float as they drift through the ocean currents, creating spiky skeletal projections which can look quite striking. In addition, radiolarians form bodies which have two distinct compartments, known as the ectoplasm and the endoplasm.


The ectoplasm is the outer layer of the radiolarian's body, and it is also designed to increase buoyancy, with the use of tiny air pockets which promote floating. The endoplasm contains the structures of the body, including the cell nucleus and organelles. These two structures are typically readily apparent in cross-section.

Radiolarians eat a variety of things, including smaller zooplankton and phytoplankton, and some establish symbiotic relationships with algae, using the algae for energy and providing a space for the algae to call home. Radiolarians in turn are consumed by a wide variety of organisms, who pass them further up the marine food chain.


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