Alexandrium is an armored dinoflagellate that can
occur as single cells or in chains of two or more cells. The photo below shows a
chain of eight cells of Alexandrium. This dinoflagellate species is
described as "armored" because the cell is made up of many cellulose plates.
Alexandrium produces the paralytic shellfish poisoning (PSP) toxins, a
series of related compounds that have over 20 different versions identied so
far. A given clonal population of Alexandrium will not produce every
single possible form of the PSP toxins, but is thought to produce the same
subset of these toxins over and over again with each succeeding generation. PSP
toxins are among the most potent natural toxins known.
The individual cells of Alexandrium are not
round, but rather a bit compressed. The central groove around the cell, which
contains one of the two flagella, is clearly visible. This photograph also
contains a chain of three Alexandrium cells as well as several chains
of Pseudo-nitzschia, the domoic acid producer, for