Massive Sea Creatures We Would Not Want To Approach In The Water (Some Are Terrifying!)
The ocean holds some of the largest and most enigmatic creatures on our planet. Since many of these giants dwell far beneath the surface, it’s easy to overlook their presence—but rest assured, they are very real. From jellyfish with tentacles stretching over 100 feet to whales that rank as the biggest animals to ever exist, the sea teems with astonishing life.
Prepare to explore stunning photos and fascinating facts about the ocean’s giants—you might be amazed at what lurks in the depths!
Japanese Spider Crab
Despite their impressive size, Japanese spider crabs are surprisingly gentle creatures. With a leg span that can reach up to 18 feet and a weight of around 42 pounds, they're truly giants of the crab world.
These fascinating crabs inhabit the waters around Japan, particularly near the southern coast of Honshu. While they’re considered a popular delicacy in Japanese cuisine, declining populations have led to protective laws designed to ensure their survival for future generations.
Giant Isopod
The giant isopod is a large marine crustacean, closely related to shrimp and crabs, and it strikingly resembles a gigantic underwater cockroach. The largest individuals, sometimes called "supergiants," can grow up to 30 inches long and weigh close to four pounds.
These remarkable creatures inhabit the cold depths of the Pacific, Atlantic, and Indian Oceans. While fishermen usually steer clear of them, giant isopods aren't so picky—they often feast on fish caught in nets, making themselves unwelcome dinner guests!
Great Hammerhead Shark
Reaching lengths of up to 20 feet, the great hammerhead shark is the largest member of its species. It stands out from other hammerheads thanks to its distinctive sickle-shaped dorsal fin and uniquely shaped head.
Unlike other hammerheads, which have a more rounded, shovel-like head, the great hammerhead's head takes on a pronounced T-shape with a notch in the middle. Yet, like all hammerheads, these giants often swim in schools, moving together through the ocean.
Lion's Mane Jellyfish
Lion's mane jellyfish hold the title as the largest species of jellyfish on Earth. Often called the giant jellyfish or simply the "hair jellyfish," the biggest specimen ever recorded had tentacles stretching an astonishing 112 feet and a bell measuring 7 feet across.
These impressive measurements were documented by scientist Alexander Agassiz back in 1865 off the coast of Massachusetts. Despite their daunting appearance, lion’s mane jellyfish stings typically cause only mild, temporary discomfort and redness in humans.
Great White Shark
The great white shark is famous for both its impressive size and incredible speed. Some of the largest can grow beyond 20 feet long, weigh between 4,200 and 5,000 pounds, and swim at speeds reaching up to 35 miles per hour. Though commonly spotted near the surface, great whites are also capable of diving to depths as deep as 3,900 feet!
These powerful predators have become iconic in popular culture, especially thanks to Steven Spielberg's film adaptation of Jaws, based on Peter Benchley’s novel.
Whale Shark
Whale sharks are easy to recognize by their wide, flat heads and the unique white spots and stripes on their grayish-blue skin. These gentle giants feed by filtering water, swimming near the ocean floor to catch plankton and small fish. In Madagascar, people lovingly call them marokintana, meaning "many stars," because of their star-like pattern.
Even though they are huge—usually about 32 feet long and weighing up to 20,000 pounds—whale sharks are very calm and often let curious swimmers get close. The biggest one ever found was an amazing 62 feet long!
Sawfish
The sawfish, known for its long snout and saw-like teeth, is one of the biggest fish in the ocean. It can grow up to 25 feet long and weigh as much as 1,323 pounds.
Sawfish live in oceans all over the world and usually don't harm people unless they feel threatened. Unfortunately, all five types of sawfish are listed as Endangered or Critically Endangered by the IUCN.
Manta Ray
Manta rays, sometimes called "devilfish" because of the horn-shaped fins on their heads, are easy to spot thanks to their wide, wing-like bodies. These graceful swimmers feed by filtering water and can grow up to 23 feet wide.
Long ago, sailors had scary beliefs about them. They thought seeing a manta ray meant bad luck, and that the ray might grab a ship's anchor and pull it underwater. This is just a myth, but it shows how mysterious and impressive these ocean giants have seemed over time.
Electric Eel
Electric eels can give shocks up to 860 volts, making them one ocean creature you definitely want to stay away from. They can grow a little over six feet long and weigh up to 44 pounds.
They also have an interesting way of breeding. The male makes a nest out of his saliva for the female to lay her eggs in. Impressively, as many as 3,000 eggs can hatch from the nest all at once!
Blue Whale
Before the International Whaling Commission put a stop to blue whale hunting in 1967, these massive creatures were nearly driven to extinction. Today, their population is estimated to be only about three to eleven percent of what it was in 1911.
Blue whales hold the title of being one of the largest animals to ever live, growing up to 98 feet long and weighing as much as 190 tons. Interestingly, in this species, the females are actually larger than the males!
Sunflower Sea Stars
Sunflower sea stars are an impressive species, especially compared to the small starfish most people are familiar with. These vibrant creatures can have between 16 and 24 limbs and can grow to an arm span of about three feet.
Sadly, their numbers have plummeted since 2013 due to sea star wasting disease. This illness, which causes their limbs to disintegrate, is linked to rising ocean temperatures. Since sunflower sea stars thrive in the cooler waters of the Pacific, the warming seas have taken a serious toll on their population.
Caribbean Barrel Sponge
Known as the "redwood of the reef," Caribbean barrel sponges can reach up to six feet in diameter. They can typically be found 33-390 feet under the Caribbean sea, nestled in the coral reefs.
This species of sponge is estimated to live for hundreds, maybe thousands, of years, making it one of the best-studied sponge species. They also make for a nice habitat for many fish species. If a diver knows where to look, it is certainly an amazing sight!
Giant Clam
Documentation of giant clams dates back to 1521, with the Italian explorer Antonio Pigafetta. The species can measure up to 47-inches across, weigh up to 440-pounds, and can live in the wild for 100 plus years.
Historically, giant clams are misunderstood. For a long time, the species was thought to be dangerous, being able to close its large shell around people's limbs. The action gave the creature the nicknames "killer clam" and "man-eating clam," even though it's not an aggressive species.
Southern Elephant Seal
Southern elephant seals are known for the elephant-like appendage on the top of males' heads. The "nose" is used to produce loud roaring sounds, especially during mating season. These creatures are massive, weighing six to seven times more than a polar bear!
This species of elephant seal ranges in size depending on the region, but the largest measured is something to behold. The record-setting seal was measured at 22.5-feet long with an estimated weight of 11,000 pounds.
Orca Whale
More formidably known as "killer whales," orcas are considered the largest species of the dolphin family. They're easily spotted due to their long dorsal fin and distinct black and white coloring. This species can measure up to 32 feet and weigh around six tons.
According to National Geographic, orcas are very sociable creatures and live together in pods, typically in the cooler arctic waters. They get their nickname "killer" because of their tendency to prey on any and all sea creatures.
Ocean Sunfish
This funky-looking sea creature is called an ocean sunfish. This is the heaviest known bony fish in the world and can weigh up to 2,205 pounds during adulthood. When its dorsal fins are fully extended, a sunfish can expand its length past the typical six feet to around eight feet!
Even though it doesn't look it, the sunfish does indeed have a tail; it's just not what we normally think of as a tail. Instead of a typical fin, the sunfish has what's called a pseudotail and is used as a rudder.
Fin Whale
After the blue whale, the fin whale is the second-largest known species on Earth. The long and slender whale has a reported maximum length of 85 feet and a weight of 80 tons. Even with all of that weight, this creature is the fastest whale species.
Fin whales can reach up to 18 miles per hour and can even travel at 30 mph if the need arises. They like to live alone or with a tiny pod, and this species can live more than 80 years in the wild.
Marlin
The marlin is best known for its beautiful rigid dorsal fin and its spear-like extended snout. It's said that the common name "marlin" was derived from a sailor's marlinspike, a tool that looks very similar to this fish's "nose." Marlins can measure up to 16-feet in length and weigh a whopping 1,803 pounds.
Aside from its popularity in sport fishing, the marlin is probably best known for its involvement in Ernest Hemingway's novel The Old Man and the Sea.
Giant Squid
Giant squids are creatures with deep-sea gigantism, meaning they're substantially larger than their shallow-water counterparts. The largest giant squid to be recorded was a female that measured 59-feet in length and weighed almost a ton.
The first recorded image of these creatures in their natural habitat didn't take place until 2004, with the first film recording happening a few years later in 2012. Both instances took place off the coast of Japan. It wasn't until 2019 that scientists filmed a giant squid in U.S. waters.
Saltwater Crocodile
The saltwater crocodile is believed to be the largest of its species. Males can reach up to 20 feet in length and weigh upwards of 2,370 pounds. Salties, as they're informally called, are considered to be dangerous for anyone who intrudes on their habitat, which means if you see one, its best not to get in the water!
Since they are large creatures, there has always been speculation about the actual size of the largest. Many hunter tales speak of finding a saltie that was 33 feet long!
Basking Shark
Coming in right behind the whale shark, basking sharks are the second-largest living shark species. These sea creatures are plankton-eating and have a megamouth that houses multiple rows of tiny teeth that curve backward. Basking sharks can reach up to 26 feet in length, making them look very threatening.
Despite their large size, basking sharks lead a very go-with-the-flow lifestyle. These creatures, while rarely seen by humans, are harmless and non-aggressive toward people.
Sperm Whale
Sperm whales are the largest toothed whales, coming in at a solid 68 feet. While females will nurture their calves, male sperm whales live alone outside of the mating season.
Birthing happens every four to 20 years, with the whales living to be around 70 years old.
Leatherback Turtle
The teardrop-shell leatherback turtle is the largest living turtle species and the fourth-heaviest modern reptile. These sea creatures can grow up to a total length of seven feet and weigh a whopping 1,540 pounds.
Some form of this species has been around for over 110 million years, evolving into the modern-day leatherback turtle. These creatures prefer open ocean, following their jellyfish prey throughout the day in deeper waters and coming up to shallower waters at night when the jellies rise in the water column.
Walrus
The funny-looking tusked creatures known as walruses can grow to weigh 4,400 pounds and be around 11.8 feet long! This species is divided into two subspecies, the Atlantic and Pacific. Both are equally massive.
Walruses are typically defined by their elongated teeth, also known as tusks. These teeth can be as long as three feet and weigh up to 12 pounds. Can you imagine having an extra 12 pounds of weight in your mouth?
Manatee
Manatees, or sea cows, are herbivorous creatures known for eating up sea plants and having an almost lazy swimming style. Manatees can grow up to 13 feet long and weigh 1,300 pounds, with the females tending to be a bit heavier.
To go along with their swimming style, manatees spend around 50 percent of their day sleeping, coming up for air every 20 minutes. Sea cows are thought to be reasonably smart, having shown signs of associative learning and long-term memory.
Coral Reef Sea Snake
Coral reef snakes are highly adapted to aquatic living and hardly ever move on land. Unlike a majority of sea creatures, sea snakes do not have gills, meaning they have to surface regularly for air. They look like eels with long bodies and tails, growing up to almost five feet.
Although these creatures look extremely horrifying, they are not known to attack. They're actually considered to be pretty mild-tempered and hardly ever bite.
Atlantic Wolffish
The Atlantic wolffish is known for the natural antifreeze it produces to ensure their blood doesn't freeze in their cold environment of 30-50 degree water. These creatures can grow to be five feet long and weigh around 40 pounds.
Wolffish are extremely important in controlling sea urchin and green crab populations, two species that would run amok if not kept in check. Their large heads and strong jaws make it easy for wolffish to break through the exoskeleton of both creatures.
The Bowhead Whale
The bowhead whale is known for its large mouth, which takes up one-third of the creature's 13.1 foot-long body. With a life-span of an estimated 200 years, it is the longest-lived mammal on the planet.
Unfortunately, this species was a prime target for whalers, and the population has been severely reduced. Out of the five bowhead species, three are listed as Endangered, one as Lower Risk, and one as Conservation Dependent, with the last being most vulnerable.
Narwhal
The narwhal is known as a real-life unicorn due to the tusk protruding from its head, technically an upper canine tooth. This sea creature is considered to be a medium-sized whale, measuring around 18 feet and weighing up to 3,530 pounds.
The narwhal species lives in the arctic waters surrounding Canada, Russia, as well as Greenland. The issue here is that the water freezes over, trapping the animals underneath with no way to get air.
