/ray'dee oh lair"ee euhn/, n.
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.
[1875-80; < NL Radiolari(a) name of the group (L radiol(us) a small beam, equiv. to radi(us) RADIUS + -olus -OLE1 + -aria -ARIA) + -AN]

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      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 (test). 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.

      Asexual reproduction is by budding, binary fission, or multiple fission. Generally, the skeleton divides, and each daughter cell regenerates the missing half. In some cases, however, one daughter cell escapes and develops an entirely new shell, the other daughter remaining within the parent skeleton.

      The skeletal remains of radiolarians settle to the ocean floor and form radiolarian ooze. When the ocean bottom is lifted and transformed into land, the ooze becomes sedimentary rock. Silica deposits, such as flint, chert (chert and flint), and the abrasive tripoli, originate from radiolarian skeletons. Fossil radiolarians have been found that date to Precambrian Time (3.96 billion to 540 million years ago).

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Universalium. 2010.

Look at other dictionaries:

  • Radiolarian — Ra di*o*la ri*an (r[=a] d[i^]*[ o]*l[=a] r[i^]*an), a. (Zo[ o]l.) Of or pertaining to the Radiolaria. n. One of the Radiolaria. [1913 Webster] …   The Collaborative International Dictionary of English

  • radiolarian — (n.) 1862, from Radiolaria, Modern Latin class name, from L. radiolus, dim. of RADIUS (Cf. radius) (q.v.) …   Etymology dictionary

  • radiolarian — [rā΄dē ōler′ē ən] n. [< ModL Radiolaria < radiolus, dim. of L radius, ray (see RADIUS): from the radiating pseudopodia] any of several classes of one celled deep sea protozoans with long, slender pseudopodia and a spiny, or solid but… …   English World dictionary

  • Radiolarian — Taxobox color = lavender name = Radiolaria image width = 225px image caption = Radiolaria illustration from the Challenger Expedition 1873 76. fossil range = Cambrian Recent domain = Eukaryota regnum = Rhizaria superphylum = Retaria phylum =… …   Wikipedia

  • radiolarian — noun Date: 1875 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 …   New Collegiate Dictionary

  • radiolarian — noun Any of many marine amoeboid protozoa, of subclass Radiolaria, having filamentous pseudopodia; they have intricate silica skeletons …   Wiktionary

  • radiolarian — [ˌreɪdɪə(ʊ) lɛ:rɪən] noun Zoology a single celled aquatic animal having a spherical amoeba like body with a spiny skeleton of silica. [Many species in the phylum Actinopoda.] Origin C19: from mod. L. radiolaria, from late L. radiolus faint ray ,… …   English new terms dictionary

  • radiolarian — ra·di·o·lar·i·an …   English syllables

  • radiolarian — ra•di•o•lar•i•an [[t]ˌreɪ di oʊˈlɛər i ən[/t]] n. mcr any of various very small marine protozoans of the class Radiolaria (or superclass Actinopoda), having slender radiating pseudopods and usu. bearing an elaborate outer skeleton • Etymology:… …   From formal English to slang

  • radiolarian — /ˌreɪdioʊˈlɛəriən/ (say .raydeeoh lairreeuhn) noun any of the Radiolaria, an extensive group or order of minute marine protozoans, having amoeba like bodies with fine radiating pseudopodia, and usually elaborate skeletons. {New Latin Radiolāria,… …   Australian-English dictionary

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