The diatom genus responsible for producing domoic acid is named Pseudo-nitzschia. Unlike Alexandrium, Pseudo-nitzschia is often observed in low numbers along the California coast. This diatom can also increase in numbers rapidly, producing blooms of millions of cells per liter and dominating the phytoplankton community for extended periods of time.
Pseudo-nitzschia is a chain forming pennate diatom. There are many species within the genus Pseudo-nitzschia, and most are difficult to distinguish from one another with routine light microscopy. Some species of this diatom are known to produce domoic acid, while others do not appear to produce this toxin
The individual cells in a chain overlap their neighbor cells at the tip. This overlapping pattern progresses in a "stairstep" fashion.
Each cell contains two
chloroplasts that appear as heavily pigmented areas separated by a clear spot in
the center of the cell, which is actually the