Re: How can you determine if the organism is a protist or an animal?

Kristen - 
   Thanks for the question.  The answer to this question lies in the number 
of cells (i.e.  is it single cell or multicellular organism?).  In general, 
a protist is a free living, single cell eukaryote (as opposed to bacteria 
which are prokaryotes).  Since protists are eukaryotic, they have membrane 
bound organelles (golgi body, mitochondria, etc.) AND a membrane bound 
nucleus (conversely, prokaryotes have no membrane bound organelles or 
membrane bound nucleus).  
   
   So:  if the organism observed under the microscope is a single cell and 
if a true nucleus and organelles can be identified, then it is a protist.  
If the organism is multicellular, then it is not a protist).  

   Protists can be photosynthetic or carnivorous for energy aquisition.  In 
your case, it seems to be carnivorous.  The "feeding mechanism" used by 
protists is called phagocytosis. Phagocytosis is when a cell engulfs a 
particle, internalizing it.  Once a particle (which could be food or even 
another organism) is phagocytosed, it undergoes processes to digest it into 
nutrients utilizable by the cell. 

   Catagories of protozoa (which tend to be larger and more versitile than 
protists) include: amoebae, euglena, and ciliates (Paramecium species fall 
under this catagory).  In addition to being found in tidal pools, protozoa 
can also be found in other water supplies.  Protozoa within some water 
supplies can be a problem, because they are the causitive agent of some 
human diseases.  
   
   Hope that this helped!

   Glynis Kolling
   Graduate Student, Food Microbiology
   Rutgers University, NJ