RADIOLARIA

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RADIOLARIA

• By Cassie Gaudet
• For Geology 3213
• Date November 16th, 2005

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Outline

• What are Radiolarians?
• ? Where they occur, What they eat
• Classification
• ? Polycystines, Phaeodarians
• Evolution
• Geologic Importance
• Reproduction
• References

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What are Radiolarians?

• marine free-floating plankton
• can range from 30um to 2mm in diameter
• arm-like extensions are used for buoyancy and to
  capture prey.
• They can exist both as individuals or in
  colonies.

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What are Radiolarians? contd

• There are no recorded benthic species.
• Radiolarians often form symbiotic relationships
  with algae and dinoflagellates.

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Where they occur

• occur in all oceans, shallow seas, bays, fjords
• most abundant in the upper few hundred meters of
  oceans, but found in deep trenches of the Pacific
• max concentrations of Radiolarians associated
  with max chlorophyll. Possibly necessary for
  survival.
• Radiolarian species are
• most diverse at the
• equator, lowest at the
• poles.

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What Radiolarians eat

• Radiolarian diet includes eating zooplanktons
  such as copepods, crustacean larvae, ciliates,
  and flagellates. Also,
• phytoplankton such as diatoms,
  coccolithophores, and dinoflagellates.
• They also consume bacteria and organic
  detritus.
• They act as both particle feeders and
  predators.

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Classification

• In 1980 Levine proposed this hierarchy
• Kingdom Protista
• Phylum Sarcomastigophora
• Subphylum Sarcodina
• Superclass Actinopoda
• Class Radiolaria

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Classification contd

• A major problem with radiolarian classification
  is that separate classifications have been
  established for the Palaeozoic, Mesozoic and
  Cenozoic, and little has been done to integrate
  them
• Though many fossils have been found, scientists
  still have not been able to successfully develop
  a complete classification scheme for them.

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Groups

• Two major groups
• 1) the Polycystines, with solid skeletal elements
  of opaline silica.
• 2) the Phaeodarians, with organic composition
  that results in rapid dissolution in sea water
  and so are rarely preserved.

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Polycystines

• have solid skeletal elements of simple opaline
  silica
• are subdivided into two major groups the
  basically spherical-shelled Spumellaria, and the
  basically conical-shelled Nassellaria.
• They are wholly marine, the most commonly
• preserved and therefore most studied members
• of the Subclass Radiolaria.
• 
  
  
• 
  

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Phaeodarians

• hollow skeletal elements of siliceous composition
  that results in rapid dissolution in sea water
  and consequent rare preservation in sediments
• have a mass of pigmented cells called phaeodium

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Evolution

• Oldest recorded occurrences of Radiolaria are
  from the latest Pre-Cambrian
• During the late Paleozoic Radiolaria show a
  gradual decline until the end of the Jurassic
  when there is a rapid diversification because of
  the dinoflagellates
• Evolution of diatoms in the Cretaceous had a
  significant effect on radiolarian evolution -
  competition for silica
• Radiolarian skeletons have become finer and less
  robust from this time.

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Geologic Importance

• Unusually long geologic range from latest
  Pre-Cambrian until Recent
• Radiolarian assemblages often contain 200-400
  species
• useful biostratigraphic and palaeoenvironmental
  tools

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Geologic Importance contd

• Because Radiolaria have silica skeletons and long
  geological range they are useful in the study of
  sediments which lack calcareous fossils
• Cherts and nodules within chert bands are often
  good sources for Radiolaria.
• Ophiolites and accretionary terrains often
  include chert bands and Radiolaria may be the
  only palaeontological aid available

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Reproduction

• Asexual reproduction occurs in Radiolarians. Cell
  division occurs in the nucleus. The test splits,
  and is rebuilt by the new organism. It is
  believed that sexual reproduction occurs as well,
  but this has not been confirmed.

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Radiolarian-Diatom siliceous ooze
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References

• Radiolaria.Org
• http//www.radiolaria.org/what_are_radiolarians.h
  tm
• Berkeley
• http//www.ucmp.berkeley.edu/protista/radiolaria/
  rads.html
• Kenyon College
  http//biology.kenyon.edu/Microbial_Bioreal
  m/eukaryotes/radiolaria/radiolaria.html