Hell vampire, or hell vampire squid (lat.Vampyroteuthis infernalis), – a small deep-sea cephalopod detritivorous mollusc from the family Vampyroteuthidae, allocated to a monotypic genus Vampyroteuthisinhabiting temperate and tropical waters of the world’s oceans. It is the only cephalopod known to science that spends its entire life at depths of 400-1000 m in an area with a minimum amount of oxygen dissolved in water. Due to the presence of unique retractable sensitive whip-like filaments, it is allocated to the order of vampyromorphs (Vampyromorpha), which has common features with both squid and octopus.The infernal vampire is a relict and only modern species of its squad. First described and mistakenly attributed to octopuses in 1903 by the German zoologist Karl Hun, who studied cephalopods.AppearanceThe total length of the hellish vampire is up to 30 cm. The gelatinous body is 15 cm long and, depending on the lighting conditions, takes on a velvety black, red, purple or brown color. Membranes connect all eight tentacles, each of which is covered with rows of soft needles or tendrils. Suction cups are found only at the ends of the tentacles. Transparent bulging eyes, depending on the light, change color (to red or blue), reach a diameter of 2.5 cm and are the largest in proportion to body size among all animals. Original drawing by Karl Hoon, who first described the species in 1903Adults have a pair of ear-shaped fins growing from the lateral parts of the mantle, which serve as their main means of locomotion: the flapping of the fins looks like „flying" through the water column. The beak of a hellish vampire is white. The connective tissue contains two bags that hide sensitive velar flagella, which are able to stretch much further than the tentacles and serve as true „tentacles" for the hellish vampire.Almost the entire surface of the mollusk’s body is covered with glow organs – photophores… They appear as small white discs that grow larger at the ends of the tentacles and at the base of the fins. Photophores are absent only on the inner side of the membranous tentacles. The infernal vampire is very good at controlling these organs and is capable of producing disorienting flashes of light lasting from of a second to several minutes. In addition, it can control the brightness and size of color spots.The chromatophores (pigment cells) available in most cephalopods (pigment cells) in the hellish vampire are practically not developed, since the ability to sharply change the color of the body, which is necessary for cephalopods living on the shelf, at great depths and in complete darkness, does not play a special role.Habitat and adaptationThe hellish is a rare example of deep-sea cephalopods, living, according to modern data, outside the zone of penetration of light at depths of 600-900 meters or more. This area of the world’s oceans has a special habitat known as the oxygen minimum zone. Here the oxygen concentration is too low to support the aerobic metabolism of most higher organisms. However, a hellish vampire can live and breathe normally in this zone at an oxygen concentration of 3% or more. No other cephalopod mollusc known to science and, with rare exceptions, animals of other species are not capable of this.For life at great depths in conditions of high pressure and lack of oxygen, the hellish vampire has formed several important adaptations. The infernal vampire has the lowest metabolic rate of any deep sea cephalopod. The copper-containing blood pigment hemocyanin, which gives the blood of the animal a blue color, effectively binds and carries oxygen. This is also facilitated by the large surface area of the gills. The hellish vampire has poorly developed muscles, but a rather perfect balance system, represented by statocysts, and the body density, due to the high content of ammonia in the tissues, practically corresponds to the density of sea water. This in many ways allows you to maintain buoyancy with the least effort and provides a sufficiently high mobility of the animal.At the top of the hellish vampire’s habitat, the water overhead looks to deep-sea dwellers like the sky at dusk: their sensitive eyes are able to distinguish the silhouettes of other animals floating above. To protect against detection, the infernal vampire emits its own bluish glow (see bioluminescence). The light blurs the outline of the animal, masking it from below. This strategy is called counter-illumination… The hellish vampire’s own large eyes see even the faintest flicker. A pair of photoreceptors located on the top of the head may warn the hellish vampire to move from above.Like other deep-sea cephalopods, the hellish vampire lacks an ink sac. In the event of a threat, instead of ink, it from the tips of its tentacles a sticky cloud of bioluminescent slime containing countless blue glowing balls. The light curtain, lasting up to 10 minutes, is supposed to stun the predator and give the hellish vampire the ability to hide in the dark without floating far. This method of protection is used only in case of extreme danger, since the regeneration of mucus requires high energy costs.DevelopmentLittle is known about the ontogeny of the hellish vampire. In the process of development, they pass through three morphological forms: the youngest individuals have one pair of fins, in the intermediate form, animals grow a new pair, and, finally, in adults, the first pair of fins degenerates and again one pair remains. As the animal grows, the surface area to body volume ratio decreases and the fins change size and position to achieve optimal movement. Juveniles mainly use a jet stream for movement, while adults prefer to use fins. This unique ontogeny has led to the fact that in the past, different forms of an animal were taken for different species of separate families.If parallels can be drawn with other deep-sea cephalopods, the hellish vampire is likely to rarely breed, laying few large eggs. Growth is slowed down due to lack of nutrients at depths typical for the animal’s . Due to the huge volume of the habitat and the rarity of the population, the meeting of two individuals for the purpose of reproduction becomes a random event. The female can store spermatophores hydraulically implanted by the male for a long time before she is ready to fertilize eggs. After fertilization, she can carry them for up to 400 days, until the juveniles hatch. Closer to its appearance, the female stops eating and dies soon after.The juveniles, which are about 8 mm long, are almost fully formed miniature copies of adults. They are transparent, they do not yet have membranes between the tentacles, their eyes are smaller, and the flagella are not fully formed. For some, not yet definite time, the fry, before they begin to feed, live on rich internal reserves of nutrients. Juveniles are often found at great depths, where, presumably, they feed on organic debris falling from the upper layers of the ocean.BehaviorEverything that is known to date about the behavior of the infernal vampire is derived from random encounters with automatic deep-sea vehicles. When caught, animals are often injured and are able to live in the aquarium for no more than two months. In addition, it is difficult to obtain reliable information on non-defensive behavior in artificial conditions.Infernal vampires have been observed to drift along with deep currents, releasing long velar flagella. If the flagella come in contact with an object or feel an external vibration, the animals become agitated, making rapid, chaotic movements. They are able to swim at speeds of up to two body lengths per second, accelerating for about five seconds. Their weak muscles, however, severely limit their endurance.Cephalopods living in more hospitable conditions can afford high energy costs for prolonged acceleration. In contrast, the hellish vampire had to develop other, energy-efficient methods of evading predators. To make hunting difficult, they use the previously mentioned bioluminescent „fireworks" in combination with wriggling glowing tentacles and unpredictable chaotic trajectories of movement.In a defensive posture, the so-called „pumpkin pose", the hellish vampire turns the tentacles with membranes inside out, covering the body, and takes on a visually larger form with threatening needles exposed outward. The inner surface of the tentacles with membranes is pigmented and almost completely hides the photophores. The glowing tips of the tentacles are brought together well above the head, deflecting the attack from vital parts of the body. If the predator bites off the tip of the tentacle, the animal will grow it back.Infernal vampires feed on detritus. More detailed studies of the anatomy of the long filamentous outgrowths made it possible to understand how the hellish vampire feeds. These outgrowths are covered with sticky hairs, and when the mollusk keeps them afloat, all kinds of small things stick to them. He then brushes off what is stuck with the main tentacles that form the cloak, and packs the debris into mucus. After which it remains only to swallow the resulting slimy lump.Genetics Molecular geneticsDeposited nucleotide sequences in the database EntrezNucleotide, GenBank, NCBI, USA: 30 (as of February 19, 2015).Protein sequences deposited in the database EntrezProtein, GenBank, NCBI, USA: 41 (as of February 19, 2015).