Distribution of tetrodotoxin in the tissues of the flatworm Planocera multitentaculata (Platyhelminthes).

tetrodotoxin distribution in various tissues of the flatworm Planocera multitentaculata was examined. The oviduct was most toxic (2000-3240 MU/g), followed by digestive organs (900-1400 MU/g), oviduct-free genital organs (430-590 MU/g), etc. The mucus secreted also showed some lethal potency. On the other hand, the eggs laid, whether in laboratory aquarium or on coastal rocks, exhibited an extremely high potency up to 10,700 MU/g. It was suggested from these findings that flatworms possess tetrodotoxin as a defense or alarm substance against predators.