Deep-sea chimaera
Image credit: NOAA Okeanos Explorer Program

The ocean is bursting with life, filled with creatures of all shapes and sizes. Most people recognize iconic marine animals like the bottlenose dolphin or great white shark. But there’s so many more creatures that call the ocean home. Some more unusual animals are often found in deeper waters, as the extreme conditions of this dark and highly pressurized environment force animals to evolve some bizarre adaptations in order to survive. Extra slimy skin, large eyes, flexible skeletons, and bioluminescence are just some of the unique adaptions these creatures use to live in their respective habitats.



Striped anglerfish
Striped anglerfish (Antennarius striatus). Image credit: SEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC.

Dive far enough down into the ocean, and you’ll reach a place devoid of light but full of organisms known for their extraordinary adaptations to this extreme environment. Many, for example, lack eyes or have slimy skin. It is here where you will encounter such creatures as the elusive giant squid, bright red giant tubeworms, and goblin sharks. Perhaps the most fascinating of these creatures, with its fishing pole appendage and bioluminescence, is the anglerfish.

Anglerfish belong to the order Lophiiformes, a highly diverse group of marine fishes with a wide range of body forms ranging from globose to spherical or even elongated to compressed. The heads of these animals are quite large; they houses the fish’s enormous eyes and terrifying mouth, which contains rows filled with numerous small teeth. Their coloration ranges from unmarked gray, brown, or black to multicolored complex patterns. They are distributed throughout all oceans and major seas of the world. Most are benthic as adults, typically occupying depths that range from the surface down to approximately 650 ft (200 m), with a few species extending down even further, living up to 8,200 ft (2,500 m) beneath the surface or more.

The most well-known identifying characteristic of the anglerfish, which inspires its common name, is its fishing rod-like appendage, known as an illicium. Used to lure prey out of the dark so it can strike it with its razor-toothed jaws, the illicium is an extension of the forehead, which evolved from the spines of the fish’s dorsal fin. The end of the structure has an organ that glows to entice potential prey living in the darkest regions of the ocean. Some species also have luminous tendrils that look like seaweed trailing from their chins, which are also used to attract prey.

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Frilled Shark

Underwater picture of a frilled shark
Image credit: © Citron / CC BY-SA 3.0

Upon first glance at this serpentine creature, you may wonder if you are looking at an eel. The long, snake-like appearance of the frilled shark (Chlamydoselachus anguineus) is thought to have inspired the tales of huge sea serpents from long ago. But despite its appearance, the frilled shark is certainly a shark. Named for its strange appearance, this creature has unique gills very similar to the frilly collars worn in the Elizabethan Age (think William Shakespeare, for example).

The frilled shark, also known as the lizard shark or the scaffold shark, has several distinct morphological characteristics. Its slender eel-like shape ends in an elongate caudal, or tail, fin without a lower lobe. It has a single, small dorsal fin located towards the end of its tail, and a terminal mouth with a short, blunt snout and long lower jaw. Its large mouth is armed with rows of needle-sharp, three-pronged teeth used for catching squid, fish and smaller sharks. Frilled sharks are a chocolate brown color with six pairs of frilly gill slits (most sharks only have five). The first pair encircles its entire neck, giving it its unique frilled look.

Frilled sharks are slow-moving in deep waters, among the slowest of all shark species. Found mostly on continental shelves and near the shores of large islands, they are occasionally reported in open waters as well. They mostly are benthic, meaning that they can live at depths ranging from 330 to over 4,200 feet (100-1,300 meters). As bottom-dwellers, frilled sharks’ role in their marine ecosystem may be to remove decomposing carcasses.

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Pelican Gulper Eel

Dried specimen of the pelican gulper eel with its jaw opened wide
Image credit: Alexei Orlov / CC-BY-3.0 (Wikimedia Commons)

The gulper eel, whose scientific name is Eurypharynx pelecanoides, is a bizarre-looking fish that lives deep under the sea. Because these creatures live so far down in the ocean, it’s difficult for scientists to study them well. Almost all the information we currently have about these eels comes from studying specimens that became accidentally entangled in the nets of deep-sea fishermen.

Though it’s called an eel, its appearance is actually quite different from most other animals that are considered a part of the eel family. Unlike most marine eels, this bizarre animal has the following features: a long, wide jaw; a small abdomen; extremely small pectoral fins; no scales; extremely tiny teeth; and a photophore (glandular organ that looks like a glowing spot) on the tip of its tail. In addition to these strange features, perhaps the oddest part about this deep-sea creature’s appearance is its enormous, expanding mouth that earned it several nicknames, such pelican eel, pelican gulper, and umbrella-mouth gulper. They are not to be confused with the Saccopharynx ampullaceus, which is also sometimes called a gulper eel or pelican-fish.

These trademark mouths are loose and hinged in a way that allows them to swallow animals that are far larger than themselves, such as large squid, if necessary. Because they have such tiny teeth, however, scientists believe that they probably don’t often eat big animals; they would probably only do this if there was a food shortage.

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Giant Squid

Two scientists inspect the remains of a giant squid
Image credit: NTNU University Museum

One of the most recognizable deep-sea creatures in pop culture and folklore, the giant squid (Architeuthis dux) has captured the human imagination for centuries. Aristotle, the famous Greek philosopher, wrote a description of the squid as early as 350 BCE, calling it teuthos. Known also as the kraken, the squid earns its name due to its enormous size: Scientists estimate that female giant squids can grow up to 43 feet (13 m) long! Don’t confuse the giant squid with the slightly larger colossal squid (Mesonychoteuthis hamiltoni); they’re two completely different species, although they both belong to the order Oegopsida.

Many could easily point out a giant squid due to its unique appearance. They have extremely large eyes, the largest of any animal with a diameter of up to 10 inches (25 cm). For perspective, that is about the size of a human head! There’s a reason why these eyes are so big; as creatures of the deep, the squid needs massive eyes to see in the dark. Like other species of squid, they have 8 arms and 2 tentacles. A giant squid’s arms have rows of suckers, and their tentacles, which they use to hunt, are longer than the rest of their body. Females are generally larger than males, with females reaching lengths of up to 43 feet (13 m) and males 33 ft (10 m).

Despite being such an easily recognizable creature, we actually don’t know too much about the giant squid since it lives so far down beneath the ocean’s surface. Up until 2013, scientists couldn’t come to a consensus on how many species of giant squid there actually are. Now, however, evidence seems to support that there is likely only one species of giant squid.

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Goblin Shark

Pointy-nosed blue chimaera
A pointy-nosed blue chimaera (Hydrolagus trolli). Image credit: Citron / CC-BY-SA-3.0

When people hear the word “shark,” images of the great white or shortfin mako might come to mind before the elusive goblin shark, a deepwater shark that can live almost 4,000 ft (1,200 m) beneath the surface of the ocean. Also known as the elfin shark, Mitsukurina owstoni is the only known living member of the family Mitsukurinidae. This family stretches back as far as 125 million years, to the early Cretaceous period! For comparison, the Tyrannosaurus lived only about 68 million years ago. This shark is definitely ancient and has some older morphological features, leading to many calling it a “living fossil.”

Just as other sharks are known for their unique appearances, like the hammerhead shark, the goblin shark also has some incredibly distinct physical characteristics that make it stand out. Its nose is perhaps its most recognizable feature, poking far out beyond its jaw. Like other sharks, the goblin shark has electroreceptors in its nose to detect prey and possesses a flexible skeleton, being a cartilaginous animal. It has a long, likely pink or purplish body.

Little is known about the diet of the goblin shark; it is believed, however, that they eat squid and crustaceans. There are no records of any pregnant goblin shark, so scientists know virtually nothing about this animal’s reproductive habits, either. Since it belongs to the order Lamniformes, it could give birth to live pups like others in this classification do. It is unknown what the size of a litter of goblin shark pups would likely be, although shark litters usually range between 2 to 20 pups.

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Ghost Shark

Deep-sea chimaera
Image credit: NOAA Okeanos Explorer Program

When thinking of bizarre deepwater creatures, the iconic anglerfish or blobfish might come to mind. But the deep ocean is home to a wide array of wildlife, and plenty of other fascinating critters also live there, like the spooky-looking chimaera, or ghost shark. Also commonly known as the rabbitfish, the ghost shark is not actually a single species. This term refers to animals in the order Chimaeriformes, which contains three distinct families: Callorhinchidae, Chimaeridae, and Rhinochimaeridae. Together, these three families all contain roughly 50 living species that can be found throughout the world. To make matters even more confusing, the ghost shark isn’t actually a shark, but rather a cartilaginous fish (similarly to how the gulper eel isn’t actually an eel, despite its name). So, when someone talks about ghost sharks, just know that there are a number of different fish they could be referring to.

The ghost shark is an exclusively deep-sea marine fish that can live thousands of feet beneath the surface of the ocean, with most living at or beneath 660 ft (200 m). Scientists have recorded the pointy-nosed blue chimaera (Hydrolagus trolli), for example, at depths of almost 6,560 ft (2,000 m), and some species can have been recorded even deeper than this!

The ghost shark earns its name for its distinct appearance. Its eyes, particularly, play a large role in its naming; they contain a reflective tissue layer, making them look pale and somewhat ghostly. Other noticeable features of this fish include its gills. Unlike most real sharks, the ghost shark does not have five gills, but only one on each side. The various species of ghost shark come in many different colors, from pale off-white to bluish to even speckled brown.

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Black-and-white illustration of the blobfish
1918 illustration of the blobfish (Psychrolutes marcidus) by Alan Riverstone McCulloch. Image available courtesy of the Internet Archive.

Many people know about the blobfish (Psychrolutes marcidus) from the viral memes and other images that showed up on newsfeeds and dashboards a couple of years ago. These pictures introduced the Internet to a sad-looking, large-nosed, gelatinous fish that was voted the “World’s Ugliest Animal” in a 2013 Ugly Animal Preservation Society poll. These images were a bit misleading about this animal’s real appearance, however. The reason this particular blobfish, Mr. Blobby, looked so sad and floppy was because he was removed from his highly pressurized environment and submerged in chemicals to aid in preservation. This made his skin color grayish and pale and tightened his skin, resulting in his nose looking droopy.

Blobfish don’t normally look like sad old men, despite what the Internet may have initially said. Since they live several thousand feet under the sea (600 to 1,200 m), they have evolved to be well adapted to handling the pressures of the ocean present at this depth and subsequently lack a swim bladder. As such, taking them out of their specialized environment vastly changes their appearance due to decompression. Blobfish typically have small eyes and gills and a pinkish, rounded body that is much shapelier than poor Mr. Blobby. Scientists have recorded males reaching almost a foot in length (30 cm).

Psychrolutes marcidus are difficult creatures to study because scientists can’t exactly study them well in their natural environment and Mr. Blobby is a testament to what happens to their appearance when removed from the ocean depths. Despite the scientific community not knowing all that much about this fascinating creature, it seems that Psychrolutes marcidus is a pretty chill animal. Like most other deepwater creatures, it moves at a relatively slow pace. This sedentary lifestyle seems to work for them! You do you, blobfish, you do you.

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Giant cuttlefish with an Eastern Blue Groper fish in its mouth
Cuttlefish consuming an Eastern Blue Groper. Image credit: Elaine de Jager by CC-BY-SA 4.0

The term “cuttlefish” does not refer to a single species, but rather all animals belonging to the order Sepiida. To make matters just a bit more misleading, cuttlefish aren’t even fish, much like how the ghost shark is not a shark or how the pelican gulper eel is neither an eel nor a pelican. These creatures actually belong to the phylum Mollusca, a large phylum that includes land snails and clams, and the order Cephalopoda, which also contains squids and octopuses.

These cute little guys are curious creatures that are well known for both their high intelligence and advanced camouflaging capabilities (Kaufmann, 2007). Their large, sophisticated brains that allow them to possess high intelligence for invertebrates. Like other cephalopods, cuttlefish can alter the pigments in their skin to camouflage themselves, ward off predators, and even win mates. These creatures’ camouflaging capabilities is impressive not just for how rapidly they can change colors but also because they are technically colorblind. Scientists believe that their well-developed eyes can better perceive contrast (through light polarization sensitivity), aiding them in camouflaging themselves.

Other prominent features of these animals include their w-shaped eyes (with wide-ranging vision capabilities) and cuttlebones. Unique to these animals, cuttlebones are internal structures that are used for buoyancy. Because of the delicate nature of these structures, cuttlefish will typically remain in shallow waters to avoid excess pressure, although scientists have recorded them reaching depths down to 600 m beneath the surface of the ocean (Lu, 1991).

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