The box jellyfish is the most venomous animal in the sea

According to NOAA, the Australian box jellyfish (Chironex fleckeri) is considered the most venomous marine animal on Earth. Its sting delivers a complex cocktail of toxins that can trigger paralysis, cardiac arrest, and death within minutes.

The venom is injected by nematocysts — microscopic barbed cells lining the tentacles that fire on contact like venomous harpoons. More than 70 deaths have officially been attributed to the species in the past century, though the true toll is likely higher.

Unlike ordinary jellyfish that drift passively, the box jellyfish is an active swimmer with surprisingly capable vision. It carries 24 eyes arranged in clusters around its cube-shaped bell, some equipped with a lens, cornea, and a light-adjusting iris.

It is one of the few jellyfish that can genuinely see — and steer to avoid obstacles.