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RADIOLARIA

RADIOLARIA. By: Cassie Gaudet For: Geology 3213 Date: November 16 th , 2005. Outline. What are Radiolarians?  Where they occur , What they eat Classification  Polycystines, Phaeodarians Evolution Geologic Importance Reproduction References. What are Radiolarians?.

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RADIOLARIA

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  1. RADIOLARIA By: Cassie Gaudet For: Geology 3213 Date: November 16th, 2005

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

  3. 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.

  4. What are Radiolarians? cont’d • There are no recorded benthic species. • Radiolarians often form symbiotic relationships with algae and dinoflagellates.

  5. 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.

  6. 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.

  7. Classification In 1980; Levine proposed this hierarchy: Kingdom Protista Phylum Sarcomastigophora Subphylum Sarcodina Superclass Actinopoda Class Radiolaria

  8. Classificationcont’d • 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.

  9. 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.

  10. 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.

  11. 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

  12. 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.

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

  14. Geologic Importance cont’d • 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

  15. 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.

  16. Radiolarian-Diatom siliceous ooze

  17. References • Radiolaria.Org http://www.radiolaria.org/what_are_radiolarians.htm • Berkeley http://www.ucmp.berkeley.edu/protista/radiolaria/rads.html • Kenyon College http://biology.kenyon.edu/Microbial_Biorealm/eukaryotes/radiolaria/radiolaria.html

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