Jellyfish; box jellyfish is most deadly
Most toxic: Australia and other Indo-Pacific waters
Box jellyfish






Coral reef






Portuguese Man-O-War {Physalia physalis)






A selection of various sea anemones
Box jellyfish
Coral reef
Portuguese Man-O-War {Physalia physalis)
A selection of various sea anemones
Physical contact or osmotic gradient  causes discharge of<unk> 
A spring loaded venom delivery system
Once opened, a<unk> releases all of its contained venom
Nematocysts
Toxins
Pseudoparasites
Ciguatera
Ectoparasites
Scombroid
Tapeworm
Tetrodotoxin 