Photographs taken through a microscope of the 

 armored dinoflagellates Ceraf/um(left|. Dinophysis 

 (right) and Alexandrium catene/fe (bottom). Some spe- 

 cies of Dinophysis produce toxins that can cause 

 severe diarrhea (diarrhetic shellfish poisoning) in 

 humans who eat contaminated shellfish. Alexandrium 

 catene/la produces toxins that can cause "paralytic 

 shellfish poisoning" in humans who eat contaminated 

 shellfish. Symptoms include nausea, vomiting, diar- 

 rhea, abdominal pain, and tingling or burning lips, 

 gums, tongue, face, neck, arms, legs, and toes and 

 later shortness of breath, dry mouth, a choking feel- 

 ing, confused or slurred speech, lack of coordination, 

 and even death. Scale bars are in micrometers (\un); 

 1 micrometer is one-millionth of a meter or about 

 1/25,000 of an inch. 



Phytoplankton 35 



