radiolarian

[rey-dee-oh-lair-ee-uhn]
noun
any minute, marine protozoan of the class Radiolaria, or, in some classification schemes, the superclass Actinopoda, having an amebalike body with radiating, filamentous pseudopodia and a usually elaborate outer skeleton.

Origin:
1875–80; < Neo-Latin Radiolari(a) name of the group (Latin radiol(us) a small beam, equivalent to radi(us) radius + -olus -ole1 + -aria -aria) + -an

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World English Dictionary
radiolarian (ˌreɪdɪəʊˈlɛərɪən)
 
n
any of various marine protozoans constituting the order Radiolaria, typically having a siliceous shell and stiff radiating cytoplasmic projections: phylum Actinopoda (actinopods)
 
[C19: from New Latin Radiolaria, from Late Latin radiolus little sunbeam, from Latin radius ray, radius]

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Etymonline
Word Origin & History

radiolarian
1876, from Radiolaria, Mod.L. class name, from radiolus, dim. of radius (q.v.).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
radiolarian   (rā'dē-ō-lâr'ē-ən)  Pronunciation Key 
Any of various marine protozoans of the group Radiolaria, having rigid skeletons usually made of silica. The skeletons are usually spherically symmetrical and structurally complex, containing elaborate patterns of perforations (through which pseudopods extend) and often spicules. Skeletal remains of radiolarians sink to form ooze on the ocean floor, and prehistoric radiolarian ooze has fossilized to become chert and flint.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

radiolarian

any protozoan of the class Polycystinea (superclass Actinopoda), found in the upper layers of all oceans. Radiolarians, which are mostly spherically symmetrical, are known for their complex and beautifully sculptured, though minute, skeletons, referred to as tests. Usually composed of silica, the test is elaborately perforated in a variety of patterns, forming a series either of latticelike plates or of loose needle-shaped spicules. Pseudopodia extend through the perforated skeleton. A chitinous central capsule encloses the nuclei and divides the cytoplasm into two zones. The outer cytoplasm contains many vacuoles that control the organism's buoyancy.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The buckyball shape at top is a dead radiolarian, a one-celled animal with a silica skeleton.
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