Pseudonitzschia is a genus of diatoms, which are microscopic algae found in aquatic environments. These organisms are known for their unique silica cell walls, giving them a distinct appearance under a microscope. Pseudonitzschia species are commonly found in both marine and freshwater ecosystems and play a crucial role in the food web as primary producers. Some species of Pseudonitzschia can produce toxins, particularly domoic acid, which can accumulate in shellfish and pose health risks to humans and marine life. Monitoring these diatoms is important for assessing water quality and ensuring the safety of seafood.