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.

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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.