The severity of a kind of seafood poisoning, attributed to saxitoxin (STX) and its analogs, attracted early Scientific attention to its study since the dawn of the twentieth century. There are several ways to group the oldest known STX analogs. The presence of saxiphilin, a hemolymph protein that binds STX, may explain why some xanthid crab species appear to tolerate exceptionally high levels of toxins. Toxin transformation has been observed similar to that found in bivalves. Interferents are commonly found in bivalves and other seafood matrices. In bivalves, toxin profiles are changed, sometimes to such an extreme that it is difficult to trace the origin of the toxins to the causative microalgae. During a toxic bloom, bivalve's toxin profiles usually display the full array of paralytic Shellfish toxins produced by the blooming microalgae, but these gradually change due to several species-specific chemical and enzymatic transformations.