Vampire Squid
Overview
The vampire squid is a small, deep-sea cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

 found throughout the temperate and tropical oceans of the world. Unique retractile sensory filaments justify the Vampire Squid's placement in its own order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

: Vampyromorphida
Vampyromorphida
Vampyromorphida is an order of cephalopods comprising one known extant species and many extinct taxa. Physically, they somewhat resemble octopuses, but the eight main tentacles are united by a web of skin, and two smaller tentacles are also present.-Classification:*Order Vampyromorphida**?Suborder...

 (formerly Vampyromorpha), which shares similarities with both squid and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...

es. As a phylogenetic relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....

 it is the only known surviving member of its order, first described and originally classified as an octopus in 1903 by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 teuthologist
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

 Carl Chun
Carl Chun
Dr. Carl Chun was a German marine biologist.Chun was born in Höchst, today a part of Frankfurt, and studied zoology at the University of Leipzig where, after posts in Königsberg and Breslau, he was appointed professor for biology in 1892...

, but later assigned to a new order together with several extinct taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

.
The Vampire Squid reaches a maximum total length of around 30 cm (1 ft).
Encyclopedia
The vampire squid is a small, deep-sea cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

 found throughout the temperate and tropical oceans of the world. Unique retractile sensory filaments justify the Vampire Squid's placement in its own order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

: Vampyromorphida
Vampyromorphida
Vampyromorphida is an order of cephalopods comprising one known extant species and many extinct taxa. Physically, they somewhat resemble octopuses, but the eight main tentacles are united by a web of skin, and two smaller tentacles are also present.-Classification:*Order Vampyromorphida**?Suborder...

 (formerly Vampyromorpha), which shares similarities with both squid and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...

es. As a phylogenetic relict
Relict
A relict is a surviving remnant of a natural phenomenon.* In biology a relict is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas....

 it is the only known surviving member of its order, first described and originally classified as an octopus in 1903 by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 teuthologist
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

 Carl Chun
Carl Chun
Dr. Carl Chun was a German marine biologist.Chun was born in Höchst, today a part of Frankfurt, and studied zoology at the University of Leipzig where, after posts in Königsberg and Breslau, he was appointed professor for biology in 1892...

, but later assigned to a new order together with several extinct taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

.

Physical description

The Vampire Squid reaches a maximum total length of around 30 cm (1 ft). Its 15 cm (6 inch) gelatinous body varies in color between velvety jet-black and pale reddish, depending on location and lighting conditions. A webbing of skin connects its eight arms, each lined with rows of fleshy spines or cirri; the inside of this "cloak" is black. Only the distal half (farthest from the body) of the arms have suckers. Its limpid, globular eyes, which appear red or blue, depending on lighting, are proportionately the largest in the animal kingdom at 2.5 cm (1 inch) in diameter. The animal's dark color, cloak-like webbing, and red eyes are what gave the Vampire Squid its name.
Mature adults have a pair of ear-like fins projecting from the lateral sides of the mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...

. These fins serve as the adult's primary means of propulsion: vampire squid "fly" through the water by flapping their fins. Their beak-like jaws are white. Within the webbing are two pouches wherein the tactile velar filaments are concealed. The filaments are analogous to a true squid's tentacle
Tentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...

s, extending well past the arm
Cephalopod arm
A cephalopod arm is distinct from a tentacle, though the terms are often used interchangeably.Generally, cephalopod arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. Octopuses have eight arms and no tentacles, while squid and cuttlefish...

s; however, they are a different arm pair than the squid's tentacles. Instead, the filaments are the same pair that were lost by the ancestral octopuses.

The Vampire Squid is almost entirely covered in light-producing organs called photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...

s. The animal has great control over the organs, capable of producing disorienting flashes of light for fractions of a second to several minutes in duration. The intensity and size of the photophores can also be modulated. Appearing as small white discs, the photophores are larger and more complex at the tips of the arms and at the base of the two fins, but are absent from the underside of the caped arms. Two larger white areas on top of the head were initially believed to also be photophores, but have turned out to be photoreceptors.

The chromatophore
Chromatophore
Chromatophores are pigment-containing and light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and cephalopods. They are largely responsible for generating skin and eye colour in cold-blooded animals and are generated in the neural crest during embryonic development...

s (pigment organs) common to most cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

s are poorly developed in the Vampire Squid. While this means the animal is not capable of changing its skin colour in the dramatic fashion of shallow-dwelling cephalopods, such trickery is not needed at the lightless depths where it lives.

Habitat and adaptations

The Vampire Squid is an extreme example of a deep-sea cephalopod, thought to reside at aphotic (lightless) depths from 600–900 metres (2,000-3,000 feet) or more. Within this region of the world's oceans is a discrete habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...

 known as the oxygen minimum zone
Oxygen minimum zone
The Oxygen minimum zone , sometimes referred to as the shadow zone, is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about 200 to 1,000 metres, depending on local circumstances....

 (OMZ). Within the OMZ oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 saturation
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 is too low to support aerobic metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 in most higher organisms. Nonetheless, the Vampire Squid is able to live and breathe normally in the OMZ at oxygen saturations as low as 3%; a feat no other cephalopod, and few other animals, can claim.

To cope with life in the suffocating depths, vampire squid have developed several radical adaptations. Of all deep-sea cephalopods, their mass-specific metabolic rate is the lowest. Their blue blood's hemocyanin
Hemocyanin
Hemocyanins are respiratory proteins in the form of metalloproteins containing two copper atoms that reversibly bind a single oxygen molecule . Oxygenation causes a color change between the colorless Cu deoxygenated form and the blue Cu oxygenated form...

 binds and transports oxygen more efficiently than in other cephalopods, aided by gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s with especially large surface area. The animals have weak musculature but maintain agility and buoyancy with little effort thanks to sophisticated statocyst
Statocyst
The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, echinoderms, cephalopods, and crustaceans. A similar structure is also found in Xenoturbella. The statocyst consists of a sac-like structure containing a mineralised mass and numerous...

s (balancing organs akin to a human's inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

) and ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...

-rich gelatinous tissues closely matching the density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 of the surrounding seawater.

At the shallower end of the Vampire Squid's vertical range, the view from below is like the sky at twilight
Twilight
Twilight is the time between dawn and sunrise or between sunset and dusk, during which sunlight scattering in the upper atmosphere illuminates the lower atmosphere, and the surface of the earth is neither completely lit nor completely dark. The sun itself is not directly visible because it is below...

: The highly sensitive eyes of deepwater denizens are able to distinguish the silhouettes of other animals moving overhead. To combat this, the vampire squid generates its own bluish light (bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...

) in a strategy called counterillumination: The light diffuses the animal's silhouette, effectively "cloaking" its presence from the watchful eyes below. Its own large eyes detect even the faintest of gleams. A pair of photoreceptors are located on top of its head, perhaps alerting the animal to movements above.

Like many deep-sea cephalopods, Vampire Squid lack ink
Cephalopod ink
Cephalopod ink is a dark pigment released into water by most species of cephalopod, usually as an escape mechanism. All cephalopods, with the exception of the Nautilidae and the species of octopus belonging to the suborder Cirrina, are able to release ink....

 sacs. If threatened, instead of ink, a sticky cloud of bioluminescent mucus containing innumerable orbs of blue light is ejected from the arm tips. This luminous barrage, which may last nearly 10 minutes, is presumably meant to daze would-be predators and allow the Vampire Squid to disappear into the blackness without the need to swim far. The display is made only if the animal is very agitated; regenerating the mucus is costly from a metabolic point of view.

Development

Few specifics are known regarding the ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...

 of the Vampire Squid. Their development progresses through three morphologic forms: the very young animals have a single pair of fins, an intermediate form has two pairs, and the mature form again has one. At their earliest and intermediate phases of development, there is a pair of fins located near the eyes; as the animal develops, this pair gradually disappears as the other pair develops. As the animals grow and their surface area to volume ratio drops, the fins are resized and repositioned to maximize gait efficiency. Whereas the young propel themselves primarily by jet propulsion, mature adults find flapping their fins to be the most efficient means (Seibel et al. 1998). This unique ontogeny caused confusion in the past, with the varying forms identified as several species in distinct families (Young 2002).

If hypotheses may be drawn from knowledge of other deep-sea cephalopods, the Vampire Squid likely reproduces slowly by way of a small number of large eggs. Growth is slow as nutrients are not abundant at depths frequented by the animals. The vastness of their habitat and its sparse population make procreative encounters a fortuitous event. The female may store a male's hydraulically implanted spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...

 (a tapered, cylindrical satchel of sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

) for long periods before she is ready to fertilize her eggs. Once she does, she may need to brood over them for up to 400 days before they hatch. The female will not eat towards this culmination and dies shortly thereafter.

Hatchlings are c. 8 mm in length and are well-developed miniatures of the adults, with some differences. Their arms lack webbing, their eyes are smaller and their velar filaments are not fully formed. The hatchlings are transparent and survive on a generous internal yolk for an unknown period before they begin to actively feed. The smaller animals frequent much deeper waters, perhaps feeding on marine snow
Marine snow
In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to the aphotic zone below. The term was first coined by the explorer William Beebe as he...

 (falling organic detritus).

Behavior

What behavioural data known has been gleaned from ephemeral encounters with ROVs; animals are often damaged during capture and survive for no more than about two months in aquaria. An artificial environment makes reliable observation of non-defensive behaviour difficult.

With their long velar filaments deployed, Vampire Squid have been observed drifting along in the deep, black ocean currents. If the filaments contact an entity, or if vibrations impinge upon them, the animals investigate with rapid acrobatic movements. They are capable of swimming at speeds equivalent to two body lengths per second, with an acceleration time of five seconds. However, their weak muscles limit stamina considerably.

Unlike their relatives living in more hospitable climes, deep-sea cephalopods cannot afford to expend energy in protracted flight. Given their low metabolic rate and the low density of prey at such depths, Vampire Squid must use innovative predator avoidance tactics to conserve energy. Their aforementioned bioluminescent "fireworks" are combined with the writhing of glowing arms, erratic movements and escape trajectories, making it difficult for a predator to home in.

In a threat response called "pumpkin" or "pineapple posture", the Vampire Squid inverts its caped arms back over the body, presenting an ostensibly larger form covered in fearsome-looking though harmless spines (called cirri). The underside of the cape is heavily pigmented, masking most of the body's photophores. The glowing arm tips are clustered together far above the animal's head, diverting attack away from critical areas. If a predator were to bite off an arm tip, the Vampire Squid can regenerate it.

Copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...

s, prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...

s and cnidarians have all been reported as prey of Vampire Squid. Little else is known regarding their feeding habits, but considering their environment, they are likely to be opportunists. Vampire Squid have been found among the stomach contents of large deepwater fish such as giant grenadier
Giant grenadier
The giant grenadier, Albatrossia pectoralis , is a very large rattail, the only member of the genus Albatrossia, found in the north Pacific from northern Japan to the Okhotsk and Bering seas, east to the Gulf of Alaska, and south to northern Baja California in Mexico, at depths of between 140 and...

s, and deep diving mammals such as whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s and sea lion
Sea Lion
Sea lions are pinnipeds characterized by external ear-flaps, long fore-flippers, the ability to walk on all fours, and short thick hair. Together with the fur seal, they comprise the family Otariidae, or eared seals. There are six extant and one extinct species in five genera...

s.

Relationships

The Vampyromorphida are characterized by such apomorphies as the possession of photophores, a peculiar type of uncalcified endoskeleton
Endoskeleton
An endoskeleton is an internal support structure of an animal, composed of mineralized tissue. Endoskeleton develops within the skin or in the deeper body tissues. The vertebrate is basically an endoskeleton made up of two types of tissues . During early embryonic development the endoskeleton is...

 called "gladius", 8 webbed arms and the 2 velar filaments. Until fairly recently known only from the modern species and some fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 remains tentatively allocated to this group, a batch of Middle Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 (Lower Callovian
Callovian
In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian....

, c.165-164 mya) specimens found at La Voulte-sur-Rhône demonstrated that clearly vampyromorphid cephalopods were in existence for far longer than has been hitherto believed.

These were described as Vampyronassa rhodanica
Vampyronassa rhodanica
Vampyronassa rhodanica is an extinct vampyromorph cephalopod known from around 20 fossils from the Lower Callovian of La Voulte-sur-Rhône, Ardèche, France....

. The supposed vampyromorphids from the Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....

-Tithonian
Tithonian
In the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...

 (156-146 mya) of Solnhofen
Solnhofen
Solnhofen is a municipality in the district of Weißenburg-Gunzenhausen in the region of Franconia in the Land of Bavaria in Germany. It lies within the Altmühl valley....

, Plesioteuthis prisca, Leptoteuthis gigas, and Trachyteuthis hastiformis
Trachyteuthis hastiformis
Trachyteuthis is a genus of fossil teuthid, comprising four species: T. hastiformis, T. nusplingensis, T. teudopsiformis, and T. covacevichi.-Taxonomy:The taxonomic placement of Trachyteuthis is uncertain...

, cannot be positively assigned to this group; they are large species (from 35 cm in P. prisca to > 1 meter in L. gigas) and show features not found in vampyromorphids, being somewhat similar to the true squids, Teuthida.

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