The sea wasp box jellyfish is perhaps the most deadly variety. This translucent sea-dweller may not look all that menacing, but it is the most venomous animal on planet Earth. Box jellyfish are deadly to many different animals, not the least of all, us. If you get stung by one of these animals, you are very likely to die. Even if you do not, you will be in tremendous pain for some time afterward.
There is no antivenin, which means that if you are stung, you will almost certainly be dead within minutes.
This snake may look less fearsome than the hooded cobra, but it is arguably more dangerous. It can strike very quickly and can also chase its victims at an incredible speed. It chooses to do this quite often without any provocation whatsoever.
Another ocean dweller to be wary of is the cone snail. It may not look like much, and you may easily mistake it for any other snail on the beach, but it is extremely deadly. Just one drop of its venom can kill twenty human adults.