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Spongodiscid-type radiolarians have a spongy appearance (foamy or loosely organized skeleton), are discoidal in shape and may or may not have flat extensions (arms) from the central region of the skeleton. They are common in modern sediments, are cosmopolitan in distribution, and range throughout the Phanerozoic. Their significance in modern sediments has not been fully investigated, especially with respect to their ecology.
Morphologic characteristics are investigated in this study, especially the type of matrix, spines, outer covering, and internal growth, and how it relates to environmental parameters. Spongodiscid-type distributions in the present oceans are evaluated (1) by using published reports on spongodiscid-types in modern sediments and (2) by observing samples material (SEM
and transmitting light microscope) from the Arctic, Bering Sea, Gulf of Mexico, Southern Atlantic, equatorial Pacific, California continental borderlands, Indian and Antarctic Oceans. Three groups of spongodiscid-type radiolarians were identified. (1) Spongotrochus glacialis group (robust spongy matrix, with or without spines, without arms) dominates the polar oceans. The diversity is low and the assemblage can inhabit the waters of the shelf as well as the slope. (2) Stylochlamydium venustum group (spongodiscid-type with distinct pores, spongy matrix, with or without spines, without arms) plus S. glacialis, dominate subarctic assemblages. (3) S. glacialis and spongodiscid-type with arms are found in the equatorial region. The diversity here is much greater than in any of the other ar as. These results are plotted on a world map comparing the distribution of recent spongodiscid-type with surface-water temperature, water temperature at depth 200 and 400 m (656 and 1,312 ft), surface salinity, surface and bottom currents and bottom topography of the world ocean.
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