From Aristotle describing crustaceans and mollusks on papyrus scrolls to researchers using crowdsourcing and genetic testing to identify the latest species of sunfish, humans have long been fascinated with creatures of the sea.

“It’s the unknown,” says Erich Hoyt, author of Creatures of the Deep: In Search of the Sea’s Monsters and the World They Live In. “You look out on the ocean and you might see a dolphin or a whale, but you don’t see what goes on beneath,” he says. “We know only a fraction of the number of species down there.”

Whether it’s their stunning appearance or their ruthless quest for survival, these are some of the most captivating species of sea animals explorers and marine biologists have identified.

Vampire squid

Despite their ominous name, vampire squids are relatively small, growing up to about 12 inches in length. They have a gelatinous body with webbing between their arms, giving them a cloak-like appearance.
PHOTOGRAPH BY SOLVIN ZANKL, NATURE PICTURE LIBRARY

The first thing to know about vampire squid is that they’re neither vampires nor squid, says Bruce Robison, a senior scientist at the Monterey Bay Aquarium Research Institute, who has been tracking the cephalopods for decades.

So, how did this gentle, deep-sea scavenger earn the fearsome moniker? German teuthologist Carl Chun first described the vampire squid in 1903. He named it Vampyroteuthis infernalis, meaning “vampire squid from hell.”

“I suspect that the red eyes and the cape led him to say, ‘that looks like a vampire,’” Robison says. “So he had some fun with the name.”

Instead of blood, the vampire squid feeds on what is known as marine snow—floating debris such as algae, dead plankton, and fecal matter. But it would be a mistake to underestimate this tiny cephalopod. Vampire squid can squirt mucus with luminous particles from pores at the ends of their arms, enveloping themselves in a glowing cloud to avoid predators.

Hoodwinker sunfish

Unlike the vampire squid, the hoodwinker sunfish is a newly discovered species. Classified as Mola tecta, this elusive fish was first identified in 2017 by Ph.D. student Marianne Nygaard and her team in New Zealand. “Tecta” derives from the Latin word “tectus,” meaning concealed or hidden.

“I was pretty impressed that this fish had managed to escape recognition for all of these years, despite an enormous interest in them, numerous species described, and a messy taxonomy,” Nyegaard says.

Known to inhabit cold waters in the southern hemisphere off the coasts of New Zealand, Australia, Chile, Peru, and South Africa, the blob-like mola tecta, which some estimate can weigh 2,000 pounds, has since been spotted along the coast of California and as far north as Alaska.

Sunfish can vary significantly in appearance within the same species and change morphology as they grow, making identification tricky. The latest sighting was on June 3, when a sunfish measuring 7 feet, 3 inches washed up on a beach in Oregon. Initially mistaken for the more common ocean sunfish, Nyegaard was alerted and confirmed that it was indeed Mola tecta hiding in plain sight once again.

 “I feel they’re hoodwinking me constantly,” she says.

Pram bug

A pram bug, a deep-sea amphipod, hollows out a gelatinous salp to use as protective shelter for its eggs and young.
PHOTOGRAPH BY MAGNUS LUNDGREN/ NATURE PICTURE LIBRARY

Pram bugs, known as Phronima, inhabit the twilight zone of oceans worldwide, typically 200 to 1,000 meters below the surface. Despite their maternal-sounding name, derived from the British word “pram” for stroller, these amphipods, also known as barrel shrimp, are cunning parasites.

Measuring typically less than an inch long, pram bugs prey upon salps, gelatinous creatures that resemble jellyfish. The mother pram bug uses her crab-like front claws to eat out the salp’s insides, inhabit its hollowed shell and lay her eggs inside. Once she exits, she propels the salp forward like a pram, hence the name.

When her offspring hatch, they continue the cycle by consuming the salp from the inside, while the mother also takes a bite. “The killing and hijacking of another creature is a very nice contrast to devoted motherly love,” Hoyt says.

Flower hat jellyfish

Found off the coasts of Japan, Brazil, and Argentina, the stunning flower hat jellyfish, also known as Olindias formosa, uses brilliant, multicolored tentacles to lure small fish, says Hoyt. At most six inches wide in diameter, this jellyfish alternates between the sea floor and coastal waters, according to the Monterey Bay Aquarium.

The flower hat jellyfish, though rare, sometimes appears in large groups known as blooms. This occurs when rising water temperatures create more food for jellyfish, leading to a population increase. While the sting of the flower hat jellyfish isn’t deadly to humans, it is pretty painful and can cause a rash. These beautiful yet dangerous creatures have inspired both artwork and warnings for swimmers off the coast of Argentina.

Gulper eel

The gulper eel’s large mouth allows it to engulf prey whole, including fish and invertebrates, adapting well to the scarcity of food in the deep ocean.
PHOTOGRAPH BY NORBERT WU/MINDEN PICTURES

With their black coloring and sinuous tails, gulper eels swiftly navigate the midwater zone of the eastern Pacific Ocean. However, what truly sets the gulper eel apart—and inspired its name—is its gigantic mouth.

Despite its slender body, the gulper eel’s mouth can suddenly expand like a soap bubble, allowing it to scoop up much larger prey. This adaptation serves as a backup plan for when food is scarce. However, the eel, also known as the pelican eel because its scoop-like feeding method resembles that of a pelican, primarily consumes small crustaceans due to its tiny teeth.

In 2018, a video watched more than five million times captured explorers on the Nautilus E/V observing the Muppet-like juvenile gulper eel of the related Eurypharynx pelecanoides species in action at the Papahānaumokuākea Marine National Monument in Hawaii.

Colossal squid

The colossal squid, not to be confused with the giant squid, is the largest invertebrate ever identified. Known scientifically as Mesonychoteuthis hamiltoni, this deep-sea creature was first identified in 1925 by zoologist Guy Robson after he found two of its tentacles in the stomach of a sperm whale that washed up on the shores of the Falkland Islands.

In February 2007, fishermen in the Ross Sea, located south of Antarctica and often called “the last ocean” due to its remoteness, accidentally caught one of these creatures. According to Hoyt, this colossal squid weighed approximately 1,090 pounds and was among the largest ever found.

Before this incident, live specimens had yet to be observed in their natural habitat. However, in 2023, deep-sea explorer Matthew Mulrennan captured video footage that may depict a live baby colossal squid in the Southern Ocean, hundreds of miles off the coast of Argentina. Ongoing analysis is being conducted to confirm this observation.

Archerfish

The archerfish, typically found in Southeast Asia and north of Australia, is renowned for its unique hunting abilities both in and out of the water. In the ocean, these tropical fish pursue crustaceans, but they also adapt their hunting techniques underwater to spot and shoot down spiders, bugs, and other insects found on branches and leaves in mangroves.

“They can shoot down the food by taking water into their mouth through their gills,” says Eileen Caro, a biologist at The Florida Aquarium. “Then they have an indentation on the roof of their mouths so they can shoot the water out.”

While other fish can expel water, the archerfish is known for its accuracy. Typically ranging in size from 4 to 11 inches, these fish can also leap up to a foot out of the water to capture their prey.