20 of the Most Dangerous Sea Creatures in the Deep Blue

When venom enters the human body, it can prevent the body from functioning by shutting down everything from the nervous system to the circulatory system to the muscular system. Marine animals use venom either to kill their prey before they eat it or to defend themselves against their predators.

1. Box Jellyfish

Pale blue, transparent with a top shaped like a cube, box jellyfish are beautiful creatures. But their many tentacles, that can be up to 10 feet (3 meters) long, are covered with tiny darts filled with poison, and their venom takes only a few minutes to cause paralysis, cardiac arrest or death.

The deadliest and largest box jellyfish is Chironex fleckeri, also known as the Australian box jellyfish.

2. Irukandji jellyfish

These venomous jellyfish, found in the waters of Australia, are only the size of a thumbnail.

The Irukandji jellyfish has, understandably, developed the reputation of being an invisible killer.

The initial sting may feel harmless, but half an hour to an hour later, it can cause a condition called Irukandji syndrome.

Trust us, you seriously don't want to play around with Irukandji syndrome.

It can lead to cramping, burning, nausea or brain hemorrhages.

If you, like the vast majority of people, want to minimize your risk of exposure to those unpleasant symptoms, you'll want to keep a close eye on weather reports before swimming Down Under.

3. Blue-ringed Octopus

The blue-ringed octopus is yellow with blue rings that glow like a warning light when it's threatened. Though it's typically smaller than a human hand, it's one of the most venomous sea creatures in the world.

Its venom contains the neurotoxin tetrodotoxin (TXX), which can shut down the human respiratory system and cause heart failure. But the most frightening detail is that no existing antivenom can treat its bite.

4. Stonefish

Declared the most venomous fish by the Guinness World Records, stonefish are typically found in the Indo-Pacific region at the bottom of the sea.

It's not an aggressive fish, but its rocky, bumpy texture camouflages it along the sand and coral reefs. If an unsuspecting victim steps on it, the stonefish will release its sharp dorsal spines that contain a lethal amount of venom.

5. Cone Snails

Cone snails, which are found in the Indian and Pacific Oceans, capture their prey with their venomous, harpoon-like teeth that they jab rapidly and repeatedly into their victims. Though they usually don't attack humans unless they are stepped on, their venom can kill a person with one prick.

6. Beaked Sea Snakes

Sea snake venom is 10 times more potent than the venom of a cobra. The beaked sea snake, one of the few sea snakes that are known to be aggressive, accounts for about 90 percent of human deaths from sea snake bites.

7. Puffer Fish

Puffer fish are named as such because, when threatened, they ingest a huge amount of water and air into their elastic stomachs and inflate into a spiky ball multiple times its size.

They also carry the same TXX neurotoxin as the blue-ringed octopus — enough of it to kill 30 humans. Called "fugu" in Japan, puffer fish is a delicacy, but this dish can be deadly if not prepared safely.

8. Flower Urchin

This sea creature are covered in feelers that look like a bouquet of flower petals. When threatened, the petals snap shut and inject venom into victims.

The flower urchin was named the most dangerous sea urchin in the Guinness World Records because its venom can quickly cause intense pain, respiratory problems or paralysis and cause the victim to drown.

9. Lionfish

Lionfish are striking sea creatures, with their brown and white stripes and long pectoral fins that fan out like a lion's mane. They also have long venomous spines that carry deadly poison, making them one of the most dangerous fish in the ocean.

In addition to being a danger to its prey, lionfish are also an invasive species that threaten coral reefs and other marine ecosystems.

10. Stingrays

Stingrays are generally safe and peaceful ocean creatures, but if they are threatened, they have venomous barbs along their tail that can pierce through human skin. The stingray that unexpectedly killed "The Crocodile Hunter" host Steve Irwin punctured his heart and lungs through his chest.

Marine predators have lower human death counts than other dangerous animals because most people don't traverse into the deep waters where they live, and many sea creatures only attack when they are trying to defend themselves.

1. Sharks

While sharks are fierce predators of the ocean, they generally aren't interested in humans as prey. While shark attacks often make the news and inspire movies, sharks only kill about 20 humans a year. Humans, on the other hand, kill an estimated 100 million sharks each year.

But don't mess with sharks, seriously. The most dangerous sharks include the great white shark, tiger shark and bull shark. Their teeth are made to grind, crush and sheer their prey, so even a tiny bite could do immense damage to a human limb.

2. Goliath Tigerfish

The goliath tigerfish, native to Africa, is known for its 32 jagged, dagger-like teeth. A National Geographic documentary called them "Monster Fish of the Congo," and locally, its native Swahili name "mbenga" translates to "dangerous fish."

They can grow up to 130 pounds (60 kg), and they're a rare fish that will attack smaller crocodiles. Some even believe the Goliath tigerfish to be an evil spirit.

3. Great Barracudas

The great barracuda can grow up to 10 feet (3 meters) in length and weigh over 100 pounds (46.72 kilograms). Barracudas have a reputation for being more dangerous to humans than they actually are because of their speed, aggression and multiple rows of teeth.

They don't actively attack humans, but they can sometimes mistake humans for other prey, especially while swimming in shallow waters where there is less visibility.

4. Sawfish, aka Carpenter Sharks

The sawfish, also known as a carpenter shark, is known for its long, narrow beak lined with teeth that makes it look like a double-sided hand saw.

Large-tooth sawfish, the largest species of sawfish, can reach up to 24 feet (7 meters) in length. Though they don't typically target humans, they start thrashing around from side to side when threatened.

5. Killer Whales

Most whales are friendly and don't typically target humans as prey. But orcas, aka killer whales, are the aggressive exception to the peaceful whale standard. There's even been a rise in orcas attacking boats in recent years.

6. Saltwater Crocodiles

Though saltwater crocodiles are semiaquatic reptiles, and therefore not technically sea creatures, they are often in the sea and highly aggressive. They'll chase you out of the sea and continue attacking you on land.

7. Piranhas

Piranhas also have a bad reputation because of the movies, even though they don't typically devour human flesh with their sharp teeth. However, a pack of piranhas in a feeding frenzy are extremely aggressive and likely to bite anything in sight.

8. Swordfish and Needlefish

Swordfish and needlefish are similarly dangerous, with their own unique sharp appendages they can use as weapons. Human fatalities have occurred when swordfish and needlefish have jumped from the water and pierced through their targets.

1. Electric Eel (Torpedo Fish)

Though it's called an eel and often mistaken for an eel, the electric eel is technically a fish. Each one has three electric organs that make up 80 percent of the eel's body. They can zap a person with 600 volts. For reference, humans have died with as little as 42 volts.

Electric eels are capable of delivering multiple shocks in quick succession, but even a single shock can incapacitate a human briefly and cause them to drown.

2. Marbled Electric Ray

The electric ray, which can produce 220 volts, was nicknamed the "numbfish" by the Ancient Greeks. They have electric organs on each side of their heads. A painful jolt can cause muscle pain, involuntary muscle contractions, numbness or temporary paralysis.