Saxitoxin is a neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...

 naturally produced by certain species of marine dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

s (Alexandrium sp., Gymnodinium
Gymnodinium is a genus of dinoflagellates. It is one of the few naked dinoflagellates, or species lacking armor . Since 2000, the species which had been considered to be part of Gymnodinium have been divided into several genera, based on the nature of the apical groove and the biochemistry...

 sp., Pyrodinium sp.) and cyanobacteria (Anabaena
Anabaena is a genus of filamentous cyanobacteria that exists as plankton. It is known for its nitrogen fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanobacteria that produce neurotoxins, which are harmful to...

 sp., some Aphanizomenon
Aphanizomenon is an important genus of cyanobacteria that inhabits freshwater lakes and can cause choking blooms. Studies on the species Aphanizomenon flos-aquae have shown that it can regulate buoyancy through light-induced changes in turgor pressure...

 spp., Cylindrospermopsis sp., Lyngbya
Lyngbya is a genus of cyanobacteria, unicellular autotrophs that form the basis of the oceanic food chain.Lyngbya form long unbranching filaments inside a rigid mucilage sheath. Sheaths may form tangles or mats, intermixed with other phytoplankton species...

Planktothrix is a genus of filamentous blue-green algae. Type species of the genus Planktothrix is Planktothrix agardhii Anagnostidis & Komárek. The genus was scrutinized in 2002 by S. Suda . Before, some species of the taxon were grouped within the genus Oscillatoria.- Species :* Planktothrix...

 sp.). Ingestion of saxitoxin (usually through shellfish contaminated by toxic algal blooms) is responsible for the human illness known as paralytic shellfish poisoning
Paralytic shellfish poisoning
Paralytic shellfish poisoning is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks . These shellfish are filter feeders and, therefore, accumulate toxins produced by microscopic algae, such as...