Microdistribution of tetrodotoxin in two species of blue-ringed octopuses (Hapalochlaena lunulata and Hapalochlaena fasciata) detected by fluorescent immunolabeling

► Tetrodotoxin presence was demonstrated in previously unknown tissues (brachial heart, gills, nephridia, and Needham's sac). ► Tetrodotoxin was concentrated in secretory cells lining the tubules of the posterior salivary (venom) gland. ► Tetrodotoxin was present in channels running through the dermis, suggesting a transport mechanism in the blood of the octopus. ► This is the first report of TTX in any cephalopod (Octopus bocki) outside of the genus Hapalochlaena.