Sponges  contain  spicules  made  of
   either  calcium  carbonate (Calcarea) or silica (Silicea) that provide
   support.
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   They lack tissues; there are a few specialized cell types.
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<BR><LI> Epidermal cells form a outer layer called the epidermis.
<BR><LI> Porocytes  allow  water to enter a cavity (spongocoel) and out via
the Osculum.
<BR><LI> Choanocytes  use  flagella  to  move  water  and  engulf  food  by
phagocytosis.
<BR><LI> Amoebocytes  transport  nutrients  to other cells and also secrete
the spicules.
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   Fertilization is external:  <A ClAsS=MID Href="../../../med/Vid/Johnson4e/Wmv/Sponge_Reproduction.wmv" oNClick="popurlt('../../../../med/Vid/Johnson4e/Wmv/Sponge_Reproduction.wmv');txtcolor('sponge1','gray');return false;" Id=sponge1><iMg sRc="/images/wmplayer.gif" aLt='' boRDer=0></A>
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