In order to observe the silicification process of polycystine radiolarians, we tried to culture Streblacantha cf. circumtexta with the addition of dissolved silica (final concentration 10 μM) and f/2 culture medium from 25th, Nov. to 27th, Nov., 2009. During our session of observation, one cell of S. cf. circumtexta (Pylonioidea, Spumellaria) formed siliceous fragments in the extracapsulum part of the protoplasm, which were subsequently ejected. A total of 94 siliceous fragments were thus expelled from the cell by using the low-contrast thin (LCT) pseudopodia. Similar siliceous fragments were often found in the extracapsulum of many pylonioid spumellarians, suggesting they did also secret isolated siliceous fragments. Pylonioids may silicify continuously, and the normal growth rate of the siliceous skeleton is maintained by the disposal activity of excess silification.
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