The deep sea is a very inhospitable place with no light and barely any oxygen in the water. The plant life, which is the primary energy producer, is virtually non-existent. Anything that is not a predator has to live on dead particles drifting down from the top layers of the sea. Yet life thrives there far more diverse and numerous than anywhere else on Earth. The extreme conditions of deep sea have led to extreme evolution and bizarre characteristics. Here are some facts about deep-sea creatures that illustrate the strangeness of life at extreme depths.

1 There is a fish called the Atlantic wolffish which produces its own antifreeze to keep the blood flowing. 

Atlantic wolffish are primarily found in the east and west coasts of the Atlantic. They love cold waters at depths of 20 to 500 meters (66 to 1,640 feet) at temperatures -1 to 11 degrees centigrade (30 to 52 degrees Fahrenheit). As they live in near-freezing temperatures, they can naturally produce antifreeze to keep their blood moving smoothly.

Another interesting fact about the wolffish is that they do not eat fish. Instead, they eat hard-shell mollusks, crustaceans, and echinoderms such as large whelks, cockles, sea clams, and sea urchins. They have very strong jaws with an extensive teeth structure which gives them the name “wolffish.” They also have scattered, serrated teeth in their throat. Their appetite for hard-shelled sea creatures has earned them the name “steinbítur” in Iceland, which literally means “stone biter.” (source)

2 When anglerfish mate, the male latches onto the female’s body and fuses to her losing all his internal organs until they share a bloodstream. 

The male anglerfish are considerably smaller in size than the females and do not have bio-luminescent lure above their mouths. Instead of constantly searching for a female to mate, the male anglerfish have evolved into a permanent parasitic mate. So, when a young male finds a female, it latches onto the female’s body with sharp teeth. Gradually the male physically fuses with the female’s skin and bloodstream. It also loses its eyes and all internal organs except the testes. The female anglerfish often have six or more males latched onto them like this. (source)

3 There is a deep sea cephalopod called the “vampire squid” which can literally turn itself inside out when under attack.

The vampire squid is a small cephalopod reaching up to 30 centimeters long with a gelatinous body that is either velvety jet-black or pale red in color. It is mostly found in extreme deep-sea conditions of tropical and temperate oceans. Its body is almost completely covered in light-producing organs that produce flashes of light to disorient its prey. It has eight tentacles which are connected by a webbing of skin.

Whenever there is a threat, the squid assumes a threat response called a “pumpkin” or “pineapple” posture. It bends its webbed tentacles backward making itself look larger than it is. The underside of the webbed skin is heavily pigmented. When it’s inverted, it covers all its critical body parts and masks the bioluminescence. The glowing tips of its tentacles reach far above its head diverting its attacker. If the tips are bitten off, the squid can simply regrow them. (source)

4 Upon reaching adulthood, the male flabby whalefish fuses its mouth shut and stops feeding. It loses its stomach and esophagus and uses the energy from previous meals to grow a massive liver which supports the fish for life. 

Flabby whalefish are one of the most deep-living fish found in depths ranging from 1,000 to 4,000 meters (3,280 to 13,123 feet). The adult whalefish show extreme sexual dimorphism. The females have flexible stomachs and long jaws which allow them to eat prey that is otherwise too large for them. The males fuse their mouths shut during their transformation from the juvenile phase to adulthood. They continue to metabolize the shells of the prey they ate in juvenile form, a trait which might have evolved in response to food scarcity at such depths. Without any feeding taking place, the stomach and esophagus become redundant. The energy from the mixture of saliva and previously consumed copepods is used to form a large liver which supports them throughout their adult life. (source)

5 The blobfish actually looks as normal as any other fish. It just decompresses when its taken out of extreme depths in which it lives. 

The blobfish lives at depths of 600 to 1,200 meters (2,000 to 3,900 feet). At such depths, the pressure is almost 60 to 120 times that of pressure at sea level. Many bony fish have two, gas-filled sacs called “swim bladders” which control their buoyancy. It helps them stay at their current depth without having to spend energy swimming. But a swim bladder is inefficient for maintaining buoyancy for blobfish at the extreme depths it lives in. Instead, its flesh is made of a gelatinous substance that is slightly less dense than water. This allows them to float over the sea floor without spending energy on swimming. So, when its taken out of the deep sea, its body decompresses and, not being bony, it loses its shape. (1, 2)

6 Because of their extremely narrow posterior, the anus of slender snipe eels is actually located on its throat. 

As their name suggests, the slender snipe eels have narrow bodies which taper towards their posterior. This is also why, despite reaching 1.5 meters (5 feet) in length, they weigh only a few ounces. Their narrow body consists of 750 vertebrae; that’s more than that of any other animal on Earth. However, their narrowness also caused their anus to move forward during their evolution and is now on their throats. Visually, their distinguishing feature is the mouth which looks just like that of the snipe bird, after which the eels were named. They also have very large eyes for their body size. (1, 2)

7 There is a deep-sea fish called “barreleye” that has a see-through head and green cylindrical eyes that can rotate.

The barreleyes or spook fish are commonly found in the waters of the Atlantic, Pacific, and Indian Oceans. They have large, barrel-shaped, telescoping eyes that are directed upwards or forwards. The eyes have an exceptionally high number of rod cells but no cone cells. In addition to their excellent vision, the barreleyes have a transparent, dome-shaped head with a refractive index similar to that of salt water. This allows the eyes to collect even more light as well as protect them from stinging cells on fish from which the barreleyes are believed to steal food. (source)

8 As they mature, the olfactory organs of the male gulper eels become enlarged while their teeth and jaws degenerate. The enlargement is to help them locate their mates by sensing the pheromones released by the females. 

The gulper eels, or pelican eels, can be found in the temperate and tropical regions of all oceans. They are named after pelicans because their large mouth which is almost a fourth of its total length and resembles the beak of the birds. Unlike the males which undergo enlargement of olfactory organs and degeneration of teeth and jaws, the females remain relatively unchanged as they mature. Scientists believe that soon after reproduction, the eels die. (source)

9 There is a species of worm known as “pigbutt worm” or “flying buttocks,” and it resembles a disembodied pig’s butt. 

Pigbutt worms are usually found at depths between 875 and 1,200 meters (2,800 and 4,000 feet) where oxygen levels are extremely low. They are roughly the size of hazelnut. Like all worms, they have a segmented body. Their round shape is because the two middle segments are highly inflated. They have no ability to swim and are observed just floating around with their mouths facing downward and the rear end facing upward. They produce clouds of mucous to capture food particles which they suck back into their mouths and digest. (source)

10 There is a creature called “thieving pram bug” which devours the insides of a salp before crawling inside and laying eggs. It propels the hollowed nursery to provide her larvae with fresh food and water. 

The thieving pram bug, or phronima, is found throughout the world’s oceans except in the polar regions. Though they are commonly called parasites, instead of constantly feeding off a living host as parasites usually do, the females use the hollowed out gelatinous shells of salps as prams for the larvae. Salps are barrel-shaped creatures that look similar to jellyfish. The female thieving pram bugs hook their claws into the salp’s exoskeleton to propel it through the water as the larvae develop. (1,2)