Binds specifically to sodium channels (Nav) of the axonal membrane of crayfish and prolongs the falling phase of the action potential. It also increases the maximum rates of rise of both action potential and resting potential (PubMed:6107210). Is only active on crustaceans. Contains 4 disulfide bonds. LD(50) is 10 pg/kg when injected into crabs. Belongs to the sea anemone short toxin (type III) family. PubMed:12676443 describes this protein as coming from E.ramsayi, which is considered in this reference as a synonym of E.quadricolor.