Venomous snake
Belcher's sea snake ("Hydrophis belcheri"), which many times is mistakenly called the hook-nosed sea snake ("Enhydrina schistosa"), has been erroneously popularized as the most venomous snake in the world, due to the first edition of Ernst and book, "Snakes in Question: The Smithsonian Answer Book", published in 1996.
Prominent venom expert Associate Professor Bryan Grieg Fry has clarified the error: "The hook nosed myth was due to a fundamental error in a book called "Snakes in Question". In there, all the toxicity testing results were lumped in together, regardless of the mode of testing (e.g., subcutaneous vs. intramuscular vs. intravenous vs. intraperitoneal). As the mode can influence the relative number, venoms can only be compared within a mode. Otherwise, it's apples and rocks." Belcher's sea snake's actual LD (recorded only intramuscularly) is 0.24 mg/kg and 0.155 mg/kg. Studies on mice and human cardiac cell culture show that venom of the inland taipan, drop by drop, is the most toxic among all snakes.
Conus geographus
The geography cone is highly dangerous; live specimens should be handled with extreme caution. "C. geographus" has the most toxic sting known among "Conus" species and is responsible for more than thirty human fatalities. Yoshiba estimated an LD70 value (in humans) of 0.001-0.003 mg/kg. In two cases of envenomation, only 0.0002-0.0005 mg resulted in severe paralysis. Other figures estimate LD50 values of 0.012-0.03 mg/kg. These estimates make the geographic cone snail the most venomous animal in the world. The venom is a complex mix of hundreds of different toxins that is delivered through toxoglossan radula, a harpoon-like tooth propelled from an extendable proboscis. There is no antivenom for a cone snail sting, and treatment consists of keeping victims alive until the toxins wear off.
Among the compounds found in cone snail venom are proteins which, when isolated, have great potential as pain-killing drugs. Research shows that certain component proteins of the venom target specific human pain receptors and can be up to 10,000 times more potent than morphine without morphine's addictive properties and side-effects.