Diatoms   make   up  a  major  component  of  phytoplankton  (drifting
   photosynthetic organisms).
   They  have  a  two-part,  glass-like  wall made of silica which can be
   harvested as diatomaceous earth.
   Diatoms video:  <A ClAsS=MID Href="../../../med/Vid/Campbell7e/DiatomsMoving-V.swf" oNClick="popurlt('../../../../med/Vid/Campbell7e/DiatomsMoving-V.swf');txtcolor('diatom2','gray');return false;" Id=diatom2><iMg sRc="/images/shockwave.gif" aLt='' boRDer=0></A>