Alexandrium catenella

High resolution image of Alexandrium catanella. 2001 Photo courtesy of Brian Bill, Northwest Fisheries Science Center.

Alexandrium is a dinoflagellate that has two flagella that enable it to swim. One flagellum encircles the cell causing the cell to rotate and move forward, while the other extends behind the cell and controls the direction. Some kinds of Alexandrium occur in chains that, when seen through a microscope, look like small trains moving in the water. Some Alexandrium species produce toxins that cause Paralytic Shellfish Poisoning. This is what most people in Washington mean when they talk about red tides.