sax·i·tox·in 
(săk′sĭ-tŏksĭn)
(săk′sĭ-tŏksĭn)n.
A potent neurotoxin produced by certain dinoflagellates that accumulates in shellfish feeding on these organisms and consequently causes food poisoning in humans who eat the shellfish.
[New Latin Saxi(domus gigantēus), butter clam (in which the toxin was first recognized) (from Latin saxum, stone; see SAXIFRAGE) + TOXIN.]