Dolichopteryx longipes
Encyclopedia
The brownsnout spookfish, Dolichopteryx longipes, is a species of barreleye
in the family Opisthoproctidae. It is the only vertebrate
known to employ a mirror
, as opposed to a lens
, to focus an image in its eyes. This species probably has a worldwide tropical and temperate
distribution; in the Atlantic Ocean
it is known from Bermuda
, the Bahamas, the Greater Antilles
, and the Gulf of Mexico
, and in the Pacific Ocean
it is known from the California Current
region and the South China Sea
. It is found in the mesopelagic and bathypelagic zones at a depth of 500-2,400 meters (1,600-7,900 ft), but usually occurs below 1,000 meters (3,300 ft). In the Gulf of Mexico it is found shallower, at 310–460 meters (1,000-1,500 ft).
. The eyes are cylindrical and face upward, with an accessory outgrowth to the side, and are covered with a silvery layer called the "argentea" for camouflage. The upper jaw is toothless, and there is a single row of small teeth in the lower jaw. There are 13 fin rays in the pectoral fins, 10-11 ray in the dorsal fin, 8-9 rays in the pelvic fins, and 8-9 rays in the anal fin. The pelvic fins are elongated, and there may be an adipose fin. The body is transparent, covered by thin scales. There are four pairs of blotches on the peritoneal cavity
beneath the gut
, a line of chromatophore
s below the lateral line
to the position of dorsal fin, and two blotches on the base of the tail. The snout is dusky in color. The maximum known length is 18 cm (7.1 in).
s and other small crustacean
s, though as food is scarce in the deep sea it may take anything it can catch. Reproduction is oviparous, with pelagic eggs
and larva
e. The larvoid juveniles and adults are covered in a gelatinous sheath. Flexion (the curvature of the notochord
in the formation of the caudal fin) occurs at around a standard length of 13 mm (0.5 in), and metamorphosis
at a standard length of 30 mm (1.2 in). The pectoral and pelvic fins form early, as does the stomach
on the left side. Adult D. longipes exhibit paedomorphic characteristics found in the juveniles of other opisthoproctids, such as poorly developed muscles (for example the lack of ventral muscles, meaning the gut is enclosed only by the peritoneum and the skin), rudimentary scales and coloration, and the placement of the pectoral and pelvic fins on peduncles that are not connected to the body by muscles. Developed gonad
s have been observed in a 36 mm (1.4 in) male and a 40 mm (1.6 in) female. Their lifespan
is 5 years.
and reflective
optics in sight. The main tubular eye contains a lateral ovoid swelling called a "diverticulum", largely separated from the eye by a septum. The retina
lines most of the interior of the eye, and there are two cornea
l openings, one directed up and the other down, that allow light into the main eye and the diverticulum respectively. The main eye employs a lens
to focus its image, as in other fishes. However, inside the diverticulum the light is reflected and focused onto the retina by a curved composite mirror derived from the retinal tapetum, composed of many layers of small reflective plates possibly made of guanine
crystal
s. The split structure of the D. longipes eye allows the fish to see both up and down at the same time. In addition, the mirror system is superior to a lens in gathering light. It is likely that the main eye serves to detect objects silhouetted against the sunlight, while the diverticulum serves to detect bioluminescent
flashes from the sides and below.
Barreleye
Barreleyes, also known as spook fish , are small deep-sea osmeriform fish comprising the family Opisthoproctidae...
in the family Opisthoproctidae. It is the only vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
known to employ a mirror
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
, as opposed to a lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
, to focus an image in its eyes. This species probably has a worldwide tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
distribution; in the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
it is known from Bermuda
Bermuda
Bermuda is a British overseas territory in the North Atlantic Ocean. Located off the east coast of the United States, its nearest landmass is Cape Hatteras, North Carolina, about to the west-northwest. It is about south of Halifax, Nova Scotia, Canada, and northeast of Miami, Florida...
, the Bahamas, the Greater Antilles
Greater Antilles
The Greater Antilles are one of three island groups in the Caribbean. Comprising Cuba, Jamaica, Hispaniola , and Puerto Rico, the Greater Antilles constitute almost 90% of the land mass of the entire West Indies.-Greater Antilles in context :The islands of the Caribbean Sea, collectively known as...
, and the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, and in the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
it is known from the California Current
California Current
The California Current is a Pacific Ocean current that moves south along the western coast of North America, beginning off southern British Columbia, and ending off southern Baja California. There are five major coastal currents affiliated with upwelling zones...
region and the South China Sea
South China Sea
The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...
. It is found in the mesopelagic and bathypelagic zones at a depth of 500-2,400 meters (1,600-7,900 ft), but usually occurs below 1,000 meters (3,300 ft). In the Gulf of Mexico it is found shallower, at 310–460 meters (1,000-1,500 ft).
Description
The body of D. longipes is slender, the depth 12.6-14.3% of the standard length. The head comprises 29-32.4% of the standard length, with a long, pointed snoutSnout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
. The eyes are cylindrical and face upward, with an accessory outgrowth to the side, and are covered with a silvery layer called the "argentea" for camouflage. The upper jaw is toothless, and there is a single row of small teeth in the lower jaw. There are 13 fin rays in the pectoral fins, 10-11 ray in the dorsal fin, 8-9 rays in the pelvic fins, and 8-9 rays in the anal fin. The pelvic fins are elongated, and there may be an adipose fin. The body is transparent, covered by thin scales. There are four pairs of blotches on the peritoneal cavity
Peritoneal cavity
The peritoneal cavity is a potential space between the parietal peritoneum and visceral peritoneum, that is, the two membranes that separate the organs in the abdominal cavity from the abdominal wall...
beneath the gut
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...
, a line of 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 below the lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
to the position of dorsal fin, and two blotches on the base of the tail. The snout is dusky in color. The maximum known length is 18 cm (7.1 in).
Biology and ecology
The diet of D. longipes consists primarily of copepodCopepod
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 and other small crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, though as food is scarce in the deep sea it may take anything it can catch. Reproduction is oviparous, with pelagic eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. The larvoid juveniles and adults are covered in a gelatinous sheath. Flexion (the curvature of the notochord
Notochord
The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...
in the formation of the caudal fin) occurs at around a standard length of 13 mm (0.5 in), and metamorphosis
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
at a standard length of 30 mm (1.2 in). The pectoral and pelvic fins form early, as does the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
on the left side. Adult D. longipes exhibit paedomorphic characteristics found in the juveniles of other opisthoproctids, such as poorly developed muscles (for example the lack of ventral muscles, meaning the gut is enclosed only by the peritoneum and the skin), rudimentary scales and coloration, and the placement of the pectoral and pelvic fins on peduncles that are not connected to the body by muscles. Developed gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s have been observed in a 36 mm (1.4 in) male and a 40 mm (1.6 in) female. Their lifespan
Maximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...
is 5 years.
Eyes
D. longipes is unusual in that it utilizes both refractiveRefraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
and reflective
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
optics in sight. The main tubular eye contains a lateral ovoid swelling called a "diverticulum", largely separated from the eye by a septum. The retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
lines most of the interior of the eye, and there are two cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
l openings, one directed up and the other down, that allow light into the main eye and the diverticulum respectively. The main eye employs a lens
Lens (anatomy)
The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...
to focus its image, as in other fishes. However, inside the diverticulum the light is reflected and focused onto the retina by a curved composite mirror derived from the retinal tapetum, composed of many layers of small reflective plates possibly made of guanine
Guanine
Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...
crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
s. The split structure of the D. longipes eye allows the fish to see both up and down at the same time. In addition, the mirror system is superior to a lens in gathering light. It is likely that the main eye serves to detect objects silhouetted against the sunlight, while the diverticulum serves to detect bioluminescent
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...
flashes from the sides and below.