12. Ichthyosaurs

The pre-historic Ichthyosaurs comes off as an innocent-looking dolphin species. In some ways, this is true as they do look nearly like what a dolphin looks like today. Yet they are not early dolphins at all, as the Ichthyosaurs is a marine reptiles. How did this happen? Through a process called convergent evolution. This involves two species that may look alike through evolutionary stages but won’t actually be related.

This creature was quite large for its time and shares traits with a mackerel and tuna. That means that, for its time, this was likely the fastest creature in the ocean. This is held up by their powerful tails and crescent shape. Their look shouldn’t fool you, as Ichthyosaurs were horrifying and as dangerous as they come. If they lived today, they’d make even sharks afraid of them.

11. Jaekelopterus

The Jaekelopterus was an incredibly large sea scorpion that lived just under 400 million years ago. They were among the top apex predators of their time and even ate others of their own species. They were bigger than modern-day humans too, measuring out at 8 feet in length.

The Jaekelopterus were accompanied by massive, spiked claws that were fast and capable of catching anything they wanted. Jaekelopterus are arthropods along with insects, crabs, etc. Thus far, it is the largest ever discovered from this species type. Naturally, you can understand why they are among the most horrifying sea monsters in history.

10. Moby Dick (Livyatan Melvillei)

The author of the story known as Moby Dick, Herman Melville, actually patterned his story after a real event that was claimed to have happened to a crew of men. Few believed their sea tale, but after Moby Dick was published, intrigue began to set in making people wonder if this had some truth to it in some way. Was there truly a whale equal to this in history?

The quick answer is yes, and it’s even named after the author of the Moby Dick story. Named Livyatan Melvillei, this species of whale lived around 12 to 13 million years ago. It was the size of a modern sperm whale that ate other whales and anything else they felt like consuming. Modern sperm whales use suction in the water to grab food. However, Livyatan Melvillei operated like Orcas, using their teeth to bite into and tear their prey apart. That novel was certainly not a complete fiction.

9. Japanese Spider Crab

The Japanese Spider Crab is one of the freakiest sea creatures to date. First and foremost, it is important to note that this is a real crab that you can likely see at some zoos. If not, you can visit the coasts of a few Asian territories like Japan where you can likely come across some of them.

The name of the crab comes honestly, as the legs of the crab look just like regular crab legs. Except for the weird fact that they are insanely long. This makes them come off as spider-like, hence the Spider Crab name. They are horrifying sea monsters to most just based on appearance. However, they are unlikely to go after humans.

8. Leviathan

For centuries, there have been several legends surrounding a creature known as the Leviathan. It is often mentioned by the Jewish in older texts. The Holy Bible even mentions the Leviathan in the Books of Job, Isiah, and Amos as well as in Psalms. Was this creature real, if so, what was it? Some believe Leviathan was used as a metaphor for a powerful enemy.

Others believe it to be very real. Most now believe it was more than likely a giant whale. Centuries ago, there was some speculation that whales were a little larger in some parts of the world, even over what we see now. Levithan likely was one of those larger whales, obviously embellished a bit over time.

7. Bucktoothed Ghost Sharks

The Bucktoothed Ghost Shark ranks as one of the most horrifying sea monsters out there. Funny enough, despite their name, this is actually not a species of shark. Although related to them, they technically belong to the Chimaera family. Many from this family are creepy for sure, but the ghost shark really takes the cake.

There are numerous different versions of ghost shark, but we feel the bucktoothed version is likely the creepiest. It often has a darker coloring, usually black. The teeth are all sorts of jacked up and it looks like it escaped a fish mental facility. It is clearly one ugly fish that will freak you out if you see one in the water.

6. Liopleurodon

The Liopleurodon was a creature that lived during the Jurassic period, several million years ago. Like others, it was not technically a fish or natural sea-dweller. The Liopleurodon was a giant marine reptile. In the water, there were very few predators that could go up against them and live.

They grew up to 30 feet in length normally but there are fossils that seem to indicate that some grew even bigger than this. In studies of the species, we have been able to find that they had some incredibly big and sharp teeth that could rip through anything they chose to attack. They were very fast for their size and even had a great sense of smell that they used to find prey.

5. Loch Ness Monster

For several years, we have heard tales of a creature native to Loch Ness in Scotland. It has been described in numerous different ways, but the most common description paints an image of the long-extinct Plesiosaurs. They are considered the main inspiration for Nessie today, so it is possible that something like it lived in Loch Ness over one hundred million years ago.

There have been cases of animals living longer than originally assumed. Woolly Mammoths are the best example of this. We thought they went extinct well over 10,000 years ago. However, it turns out that they lived thousands of years longer and would not truly go extinct until 4,000 years ago. Could the Plesiosaurs be similar to this? Could one have lived long enough to be seen once by someone who then started the legend?

4. Dunkleosteus

The Dunkleosteus is one of the most unique creatures ever discovered. The species lived around 400 million years ago and were among the top apex predators of their time period. They routinely preyed on sharks and other predators, likely any of those mentioned on this list if they were around.

The Dunkleosteus had armor-like plating, making them impossible for other predators to truly battle against. They had one of the single strongest bites ever recorded. Scientists measured this out and determined they were able to bite with a pressure of 8,000 pounds per square inch. This is on par with the Tyrannosaurus Rex!! That is only measuring from the tip of its fang too. Phew! They were 33 feet long as well. All of this made them one of the most horrifying sea monsters known.

3. Kraken

We’ve all heard the legend of the Kraken. It was a sea monster mentioned for hundreds of years by sailors all over. They were most commonly linked to pirates who told tall tales consistently. Yet the story of the Kraken first began with the Vikings. It is widely believed that the tale of the Kraken comes from real-life accounts of giant squids.

We know it is possible that Vikings would have come across giant squids in their travels. Of course, stories about their sea travels could take on a life of their own. This is likely why the Kraken took off and ended up being used in numerous fictional stories. The fact that the origin began from real giant squids, likely found in the waters of Norway and Greenland, is very compelling.

2. Mosasaurus

If you have seen the movie Jurassic World, it is very likely you are familiar with the Mosasaurus. Remember the animal that jumped out of the ocean to attack another dinosaur flying through the air and even a shark in a Seaworld-like environment? If you do, that was a Mosasaurus.

They were giant reptiles that could choose to swallow prey whole or cut them up with their amazing teeth. The Mosasaurus was bigger than many of the biggest land dinosaurs known. They were also quite different from other reptiles. Scientists found that baby Mosasaurus spent their early life in the open ocean, making some believe that the species gave birth to live young and not via eggs.

1. Megalodon

We always hear about the Megalodon during Shark Week on Discovery Channel, but it is for a good reason. The Megaladon species has fascinated humans for years. Just think, a giant shark? Sharks now are horrifying but if the Megaladon lived today it likely would trump all other horrifying sea monsters in the world.

They measured in often more than 50 feet in length! The jaws of the shark were so large that grown adults could walk through the opening. The species was known to hunt whales, as they were likely the only big meal they could get. It is widely believed that the extinction of the Megalodon is what allowed whales to grow so large. Without another species cutting them down, they were only able to grow. The last known Meg died 3.6 million years ago, which is eery as early humanity began at this time.

BONUS CONTENT

Striated Frogfish

The Striated Frogfish is certainly one of the most horrifying sea monsters we’ve seen. They are found all across the Atlantic Ocean as well as the center of the Pacific Ocean. The Frogfish have even been known to show up in the Gulf of Mexico, the Caribbean, and the western coast of Africa. They tend to mostly live in tropical or subtropical waters, so when it gets cooler in one area they will navigate toward the warmer climate.

Despite only reaching less than 9 inches in length, the Frogfish is certainly startling. You’ll note that its extensible body and awkwardly arranged dermal spinules are freaky. Yet what makes them even odder is the forwardly extended jaw that allows them to swallow prey whole. They can even swallow creatures as big as themselves!! The species can also change color, especially when going into new environments. It takes Frogfish only a few weeks to change to their surroundings.

Green Moray Eels

On their own, eels are creepy. However, the Moray Eel family is known to be possibly the creepiest due to both where they reside and how large they can get. The most notable of the Moray Eel family is the Green Moray. Often called this due to their coloring, they can also be yellow and thus called Yellow Morays. It is a bit complicated, we know.

These particular eels tend to be located in the Atlantic Ocean from roughly New Jersey to Bermuda while also being spotted in the Northern sector of the Gulf of Mexico to South America. They are capable of reaching 2.5 meters in length or slightly over 8 feet. You’ll also see them usually in the mid-depths of the ocean, around 40 meters in or just over 131 feet deep. They can startle even the most seasoned deep divers, with their razor-sharp teeth that could rip through them if it wanted.

Giant Japanese Salamander

While some might claim that using a salamander for an article about horrifying sea creatures is cheating, we could not disagree more. This salamander is often found in the waters of Japan and happens to be closely related to the Chinese Giant Salamander too. Usually, Salamanders can look a lot like lizards but people may not be able to tell them apart.

However, the best way to do so is pretty much the skin and environment they inhabit. Their skin will be soft and almost feel like waterproof coatings. That is due to their watery habitat. Lizards do not live in or very near the water. The Giant version in Japan is capable of getting up to 5 feet and weigh around 55lbs. This is compared to the normal salamander that gets to maybe a foot or two and less than 10lbs. Coming across one of these guys in the wild could be horrifying.

Vampire Squid

We actually did not use the entire name for this creature in the header, but it’s worth noting that it is actually called “The Vampire Squid from Hell.” As one can tell, it has many fans. It does not get very large but it’s often hard to tell what it is. It looks like a cross between an octopus and a squid and even has a higher connection to octopuses. Why is it called a squid? It is thought to appear like some types of squid from the past.

In fact, it’s the only surviving creature of the Vampyromorphida family. It is widely assumed that this creature, due to being in the extreme deep sea, never truly evolved. That is why many call it a phylogenetic relict. It is often called a “Vampire” Squid for one reason. Its coloring gives it the appearance of a black coat or cloak like Dracula. It does not suck blood but you never know with some of these deep-sea creatures.

Deep-Sea Dragonfish

Few know how the Dragonfish got its name, but some feel it is due to the coloring that gives it an eerie appearance. Yet some point to the teeth it has, which are massive and capable of ripping into human flesh if it so desired. It is highly unlikely a human being would come across one in the wild, however. The Deep-Sea Dragonfish earned its name honestly, as it’s located deep in the ocean.

They do not get very large, as they reach roughly 15cm to 26cm or around 5 to 10.5 inches. In spite of their small size, they are considered apex predators in the deep-sea. This is due to their absolutely massive jaws, that are completely filled with teeth sharp enough to cut through just about anything it chooses. Due to their cranium and upper-jaw, they can open their mouths up to 100 degrees, allowing them to kill and swallow large prey. Even those more than 50% larger than it.

Stargazer

The Stargazer fish species is relatively large, with around 51 confirmed types known. They are only in saltwater and tend to be found in both shallow and deep water. Thus, they have come across humans quite often. The Stargazer gets its name from the eyes located on the top of their heads. Although, we like to think it also looks up at the stars sometimes too. The name also comes from how it catches prey!

They have a large, upward-facing mouth that they hide while burying themselves in the sand as they wait for prey. Just their weird-looking eyes will be visible and they’ll ambush prey that comes by. The species is also venomous due to its large spines just above their pectoral fin sector. It is said that their venom likely could not kill a human unless they are cut open by a lot of Stargazers or the person is allergic. Yet they are still horrifying sea creatures to look at!

Ottoia

While there are actual Ottoia creatures out there, for a long time they became the nightmare creature to think about. Why? Due to how they were utilized in books or movies. Ottoias are relatively small but what if they became gigantic?!? In the movie Deep Rising, an Ottoia creature named Argonautica showed up and scared a lot of 90s kids in 1998.

The concept of the character in the film is that it is simply an evolved version of the Cambrian Worm, which we know as the actual Ottoia. Yet if you see the movie, what they do with the character makes it one of the most horrifying sea creatures imaginable. They give it the traits of an actual giant Cambrian Worm while also making it come off similar to the Kraken. Oh my!

Gyarados

We know what you’re thinking, did they just add a Pokemon to this list? Yes, yes we did. The Gyarados is often used in Anime, which kind of takes away a lot from how horrifying it would be in real life. This is why we wanted you to see a more realistic version of the creature, should it be seen in person. As you can see, it is quite large.

This Water Type Pokemon is capable of using water abilities to take down opponents or prey. While it is quite a notably fast swimmer and impressively strong in the water, the Gyarados can also fly. Thus making it a dual-threat! It typically reaches a little over 6 feet in height as well as 230lbs+ in weight. Overall, it is not one to mess with. In real life, it would likely result in the extinction of mankind.

Jörmungandr

Those who know about Norse Mythology know all about the Jörmungandr. Of course, those who play the God of War video games might also know of it too. Those games revolve around the Greek/Roman Gods in Mythology, so connecting Norse Mythology to things made sense. The versions you might read about differ depending on where it’s used.

You might also know it a bit from Marvel Comic books or films involving Thor, due to his connection in mythology to it. In Norse Mythology, the Jörmungandr (also known as the Midgard Serpent) is so long that he can wrap all the way around Earth or “Midgard.” He keeps his tail in his mouth, almost as a protecting shield. As the offspring of Loki and Andrboda, once the serpent releases its tail, “Ragnorok” begins. In Mythology, Thor battles and slays the serpent, dying in the process.

Colossal Squid

While we’ve had a lot of fun discussing some biblical, mythological, or fictional nightmare creatures of the ocean, there is one that is very real and capable of dealing a lot of damage if it desires. Originally discovered in 1925, most did not believe it was true. We found out over the years that they are very real and they tend to be located in the cold, Southern Arctic Ocean.

They can reach a little over 1,000lbs or 490+ kilograms on average. Meanwhile, the largest known have weighed between 1,300 to 1,500lbs or 600 to 700 kilograms. In length, they have been known to reach between 30 to 33 feet or 9 to 10 meters. While one would assume they’d kill prey easily due to their size, they actually tend to be ambush predators and use bioluminescence, or the production of light, to capture prey.