Protists  are  eukaryotes,  and  comprise  a  wide
   diversity of forms.
<P>
<lI> Some are unicellular, such as the various diatoms.
<lI> Volvox  is  a  colonial protist with some specialization among the
cells.
<lI> The  sea  lettuce,  Ulva,  is  multicellular  with  differentiated
structures that resemble leaves and roots.