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Spookfish have odd eyes, not just odd name, a deep sea creature known as the brownsnout spookfish has been found to be the ….

Matt Ford - Jan 9, 2009 2:24 pm UTC

When you—or your dog, or cat, or child—look at something, you are seeing the light that that is emitted by or bounces off an object after it passes through the lenses in your eye. In fact, all vertebrates were assumed to use lenses in their eyes, at least until the recent discovery that the Spookfish, Dolichopteryx longipes , has eyes that use mirrors to produce an image. A coauthor of the paper that describes this finding, Prof. Julian Partridge, highlights this rarity: "In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes–how to make an image–using a mirror."

bent nose spookfish

It turns out there are actually two eyes, but each consists of two different parts. The top portion of their eyes point upwards to collect as much light as possible from the sun; to keep a (half) eye out for danger below, they have 'diverticular' eyes that appear as small bumps on the side of their heads. It was thought that these diverticular eyes were lensless, and provided only an unfocused glimpse at what may be near without allowing any real spatial resolution.

Although the fish was first identified over a century ago, no one had ever captured a live specimen until recently. When the specimen was being prepared for microscopy in the lab, the uniqueness of the eyes became apparent. The mirrors inside the diverticular portions of the eye were found to be composed of a multilayer stack of tiny crystal plates. What makes this different from the equivalent structure in related species is that the arrangement and orientation of the plates directed light right onto the fish's retina.

These unique eye structures allow the spookfish to see a great deal of detail even at the depths where it lives. Whereas a lens structure would allow a creature to make out the bioluminescent blobs that appear, the mirror has the advantage of being able to produce bright, high-contrast images. At this depth, extra sight can mean the difference between eating dinner and being dinner.

Current Biology , 2009. DOI: 10.1016/j.cub.2008.11.061

* Image credit: Dr. Tammy Frank, Habor Branch Oceanographic Institution

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Sea Wonder: Barreleye

Photo credit: GreenAnswers.com

Barreleye fish ( Macropinna microstoma ), also known as spookfish, are one of those deep-sea species that looks otherworldly. They’ve got transparent heads that reveal their eyes, brains, and other organs, making them a fascination of ocean scientists for generations. Before we had remotely operated vehicles (ROVs) and other equipment that could observe deep-sea life, we barely knew anything about barreleyes beyond their unique appearance.  

Description  

Barreleyes have obvious physical adaptations but their use in helping them survive is still somewhat of a mystery. They get their name from their unusual eyes, which point upward at a 90-degree angle and are large, bright green, and tube-shaped. The eyes are visible through the fish’s “cockpit” or transparent head, which is a fluid-filled area spanning from its mouth to the top of the head. The cockpit gives the fish a submarine-esque appearance while the rest of the fish is brown and pretty ordinary looking. Fully grown barreleyes are barely four inches (10 cm) in length and they have indentations where you might expect eyes to be on a fish, which are used for olfactory sensing.   

The green pigment in their eyes may be helpful in filtering out green waves from surface light and help them see bioluminescence in jellies and other creatures of the deep. In 2009, thanks to observations by the Monterey Bay Aquarium Research Institute (MBARI), we know that barreleyes can rotate their eyes to face forward to see their prey during foraging activities. Another one of their interesting adaptations to deep-sea living is their pair of large, flat pectoral fins which help the fish remain suspended and motionless in the water column and to move very carefully and precisely.   

Diet & Habitat    

The main source of food for barreleyes are likely zooplankton, microscopic animals that are plentiful in the ocean. Biologists can tell what these fish eat because of their elongated intestines and multiple caeca (lateral dilations of the gut), which are common in species specialized to digest these kinds of plankton. Most plankton don’t live as deep as barreleye, but siphonophores and other species of hydrozoans trap plankton in their tentacles and transport them to the depths below. To feed, barreleyes likely pluck zooplankton from the grips of siphonophores using their tiny mouths, which helps them to be precise and selective. We know stinging tentacles of jellyfish and other marine species can be painful, which is at least partly why barreleyes developed their translucent housing – to protect their eyes when feeding.   

Barreleyes live at extreme depths of 1,800 to 2,600 feet below the surface in Pacific waters between Japan, the Bering Strait, and Baja California. In the National Marine Sanctuary System, we’ve seen barreleye fish in the deep waters near Monterey Bay National Marine Sanctuary and they’re likely in the deep waters near the other California sanctuaries. We didn’t observe barreleye fish in their natural habitat, or even alive for that matter, until the 1990s when scientists first captured it on video using an ROV and camera. Most recently, in Monterey Bay, a Barreleye was brought up to the surface in a small mid-water trawl net. This fish stayed alive for several hours in a shipboard aquarium, where most of our current knowledge of the species was recorded.  

Life History  

Since we’ve had little contact with these fish in their environment and studying them throughout their lifespan, it’s hard to estimate their longevity, mating habits, and age of sexual maturity. With advances in technology, we can better study the species in its habitat and begin to understand it beyond its physical adaptations.   

Threats & Conservation  

More research needs to be done before we can truly understand the barreleye and its ecology and conservation needs. In only a few decades, we have seen incredible advancements in our knowledge of this creature and can expect to learn more as we can find and observe more individuals.   

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Built-In Mirrors Help Spookfish See in the Dark Ocean Depths

The odd-looking spookfish is the only vertebrate known to have mirrors in its eyes , according to a new report. The mirrors gather and focus light better than lenses, which spookfish also have, and appear to be an adaptation for living in the murky depths of the Pacific Ocean. Scientists discovered the spookfish's unusual anatomy after examining the first specimen of the fish ever caught alive. Researcher Ron Douglas found the rare specimen last year

in the deep waters between Samoa and New Zealand, but no one on the research boat knew what it was. "It caught my attention because it looked like it had four eyes, and vertebrates with four eyes don't exist," says Douglas [ New Scientist ].

In fact, the spookfish only has two. Spookfish, also known as barreleyes, are a family of deep-sea fish with tubular eyes, rather like telescopes, that point upwards to capture the minimal sunlight that filters down from above. Each eye also has a part that points downward, forming what looks like a second pair of eyes. When researcher Julian Partridge looked at sections of the spookfish eye under the microscope, he discovered that the downward-pointing parts contain mirrors, made of tiny plates of guanine crystals, that help direct light onto the retina. Partridge explains that the mirrored "diverticular" eyes help capture light emitted by other animals:

"At these depths it is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly" [ BBC News ].

The researchers reported their finding in Current Biology [subscription required] and to the best of their knowledge, it is the first report of a vertebrate eye using mirrors to see.

"In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes - how to make an image - using a mirror," [ BBC News ] said Partridge.

Related Content: DISCOVER: Splendor in the Dark , how fish glow 80beats: Fish Living a 5-Mile Deep Trench Caught on Film 80beats: Curiosities of the Deep Revealed in First Census of Sea Life Image: University of Bristol / Tammy Frank

The eyes of this unusual organism are another example of evolutionary innovation.

"The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten" [ BBC News ]. Reflecting telescopes based on the same idea—using mirrors to focus light—weren't invented by human astronomers until the 17th century.

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spookfish eye

The Fish That Cracked the Mystery of Mirror Vision

  • Javelin spookfish

Sense Light (Visible Spectrum) From the Environment

Living systems constantly receive signals from their environment that help them survive. Light (in the visible spectrum) can come from other living systems (such as fireflies) or from non-living sources (such as the sun). Survival often depends on sensing and responding to challenges like low light conditions or light that has been altered in some way. Because basic survival is at stake, living systems must excel at meeting those challenges. A well-known phenomenon is how water bends light. A stork trying to catch a fish underwater can compensate for this bending effect so that when it strikes at the fish, it has a good chance of catching it.

School of fish

  • Vertebrates

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

Introduction

Deep in the ocean, above the region of total darkness, but below the point where 99% of sunlight is filtered out lives a species of barreleye fish called the brownsnout spookfish ( Dolichopteryx longipes ). Like many other fish that inhabit this mesopelagic (or “middle of the ocean”) zone, it has two eyes that point upward.

This arrangement makes it possible to see shadows of predators, prey, or potential mates swimming above, but it doesn’t help the fish to see in  other directions or detect bioluminescence, a special light given off by other sea creatures.

The mirror reflects light and creates sharp images from a wide field of vision. This allows the brownsnout spookfish to have a clear view of what’s below it and also to detect bioluminescent light produced by other organisms.

The Strategy

Enter the brownsnout’s optical innovation: it has outgrowths from its upward-facing eyes that point downwards. While other mesopelagic fish have similar outgrowths, they lack lenses to reflect and focus incoming light, and as a result they can only see blurry shapes at best. Lenses are useful because they can bend light to focus the rays on the retina and create an image. The brownsnout, too, lacks lenses, but it does have stacks of plates that act as a mirror. The mirror reflects light and creates sharp images from a wide field of vision. This allows the brownsnout to have a clear view of what’s below it and also to detect bioluminescent light produced by other organisms.

Additionally, the plates of the mirror are angled to create a curved shape that allows the maximum amount of light to be reflected, creating the sharpest possible image. It’s also hypothesized that the fish can alter the position of the mirror to focus on objects at different distances.

The brownsnout spookfish’s downward facing eye (1) focuses light on the retina (a) using a mirror made of reflective crystals (b). The main eye (2) more conventionally uses a lens (c) to focus light on its retina (d).

Spookfish eye

In addition to the upward-pointing eye shown here, the brownsnout spookfish has additional eye structures that allow it to see what's below as well. (Credit: Florida Atlantic University)

The Potential

This strategy provides the spookfish a valuable advantage as it competes with other animals to find food and avoid becoming food in the almost-total darkness of the mesopelagic zone. And it could provide equally valuable advantages to specialty cameras and other human-made systems that would benefit from the ability to form crisp images over a broad field in extremely dim light.

close up photograph of dark brown beetle swimming in water

Eyes Allow Clear Vision in Both Air and Water

Whirligig beetles

Eyes of the whirligig beetle have different surfaces to match the refractive indexes of both air and water.

bent nose spookfish

Eyes Give 360° Vision

The eyes of the chameleon provide 360-degree vision due to unique eye anatomy and an ability to transition between monocular and binocular vision.

Last Updated August 18, 2016

The hidden powers of animals: uncovering the secrets of nature.

26/02/2021 | Dr. Karl P. N. Shuker

Spookfish uses mirrors for eyes

A novel vertebrate eye using both refractive and reflective optics.

Current Biology | 25/12/2008 | Hans-Joachim Wagner, Ron H. Douglas, Tamara M. Frank, Nicholas W. Roberts, Julian C. Partridge

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Shark Eyes Maximize Stereoscopic Vision

Great hammerhead shark

Horizontal eye stalks allow eyes to rotate forward, creating a wider field of binocular vision.

Cataglyphis ant in the Ebro Depression in Spain

How Tunsian Desert Ants Smell in Stereo

The antennae of the Tunisian desert ant create a detailed olfactory map by detecting smells in left and right channels.

Daisies extending their stems towards the sun

Water Pressure Helps Flowers Follow the Sun

Light intensity concentrates hormones that alter the water levels in cells causing plants to bend toward the light source.

close up photograph of reddish-brown ants crawling on sand

Hair Helps Cool the Body

Saharan silver ant

The hair of the Saharan silver ant keeps it cool by efficiently reflecting light and heat energy while also dissipating excess heat.

photograph of grey heron standing on a rock during the day

Head Position Helps Correct for Light Refraction

Western reef heron

The head of the reef heron corrects for light refraction at the water's surface by adjusting position and keeping a constant relationship between real and apparent prey depth.

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Spookfish Uses Mirrors for Eyes

Mirrors give fish diverticular eyes

By Catherine Schwanke | Published Jan 9, 2009 12:08 AM EST

  • Environment

Odd looking? That’s an understatement. But the barrelye, better known as the spookfish, just got its claim to fame. What makes this skinny, sea creature so special? Just look into its eyes. Literally. The spookfish is the first vertebrate discovered to use mirrors for eyes. Instead of using lenses to focus light and create images, the spookfish utilizes reflective mirrors.

At first glance, the fish looks to have four eyes (spooky, right?), but Professor Julian Partridge from the University of Bristol confirms the spookfish has only two. According to Partridge, “In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes – how to make an image – using a mirror.”

The spookfish has “diverticular” eyes which are split into two connected parts. One part of the eye looks upward into the waters above while the other, resembling a dot on the side of the fish’s head, points downward to the sea below. This setup gives the spookfish an advantage in deep waters, allowing the fish to see food above and at the same time, potential threats below.

Last year, scientists from Tuebingen University in Germany caught a spookfish off the coast of Tonga, an island in the Pacific. The spookfish was discovered 120 years ago, but until recently, a specimen had never been caught. Now who’s the cool cat…err…fish in town?

Via: News.BBC.co.uk

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  • Not Exactly Rocket Science

Spookfish eye uses mirrors instead of a lens

In the twilit waters of the deep ocean, beneath about 1000m of water, swims the brownsnout spookfish ( Dolichopteryx longipes ). Like many other deep-sea fish, the spookfish is adapted to make the most of what little light penetrates to these depths, but it does so with some of the strangest eyes in the animal kingdom.

For a start, each eye is split into two connected parts, so the animal looks like it actually has four. One half points upwards and gives the spookfish a view of the ocean above. The other points downwards into the abyss below and it’s this half that makes the spookfish unique. The eyes of all other back-boned animals use a lens to divert the path of incoming light and focus it onto a specific point of the retina. But the spookfish’s downward-facing eye uses mirrors instead, forgoing a lens in favour of hundreds of tiny crystals that collect and focus light.

This bizarre animal was first described 120 years ago, but no one had discovered its reflective eyes until now because a live animal had never been caught. Hans-Joachim Wagner from Tubingen University changed all of that by netting a live specimen off the Pacific island of Tonga.

The spookfish’s eyes are similar in structure to many other fish that swim in the ocean’s twilight zone, where darkness is heavy but not quite total. The main part of each eye is tube-shaped and points to the surface, like a vertically mounted telescope. In photos A and B below, this upward-facing half has a yellow-orange shine because the camera’s flash has bounced off a reflective layer at the back of the eye.

This shape allows the spookfish to collect as much light as possible from above and spot the silhouette of animals swimming over it. But in doing so, it sacrifices the ability to spot other sources of light around it, especially bioluminescence – light given off by other deep-sea creatures.

To detect that, the spookfish has outgrowths on the side of its eyes that point downwards. The tops of these look black in photos A and B and the bottoms have a red eyeshine in photo C, taken from below the animal. These two parts of the eye – outer and inner – may look distinct, but they are categorically the same structure, united by a common retina.

Other deep-sea fish have similar outgrowths but without a lens to focus the gathered light, they usually provide a blurry image at best. But the spookfish doesn’t need a lens – light entering its outer eye hits a mirror, made of stacks of crystals. The stacks sit roughly parallel to one another, but their angle changes over the surface of the mirror, giving it an overall concave shape.

Wagner used a computer simulation to show that mirror’s curve is perfect for focusing reflected light onto the fish’s retina. It provides the animal with sharp images of what’s below it, from straight downwards to about 50 degrees in either direction. Wagner thinks that the spookfish could even shift the position of its mirror, moving it away from the retina to focus on closer objects, just as humans can alter the shape of our lenses.

Many groups of animals use reflective surfaces to help them form images, but usually, these sit behind the retina and reflect light that has passed through it. This layer – the tapetum – makes the eye more sensitive and is the reason why many animal eyes seem to glow in the dark. But in the spookfish, the mirror sits in front of the retina and its jobs is to focus, not to sensitise.

The fact that the spookfish is a back-boned animal – a vertebrate – makes its eye that much more special. Inverterbrates have a wide variety of eye designs, but vertebrates, from fish to humans, rely on just the one. The spookfish is the exception and the mirrored half of its eyes could even trump the traditional, upward-facing model. By reflecting light, rather than refracting it, these outer eyes could produce brighter images with higher contrasts that lens-carrying eyes normally would. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.

Update: If that last sentence looks familiar to anyone, it’s because it was widely plagiarised . 

Preference: H WAGNER, R DOUGLAS, T FRANK, N ROBERTS, J PARTRIDGE (2008). A Novel Vertebrate Eye Using Both Refractive and Reflective Optics Current Biology DOI:10.1016/j.cub.2008.11.061

Read This Next

Why did humans evolve to blink, this 160-million-year-old fish gouged out its victims’ flesh, see a rare view of a manta ray courtship ritual deep in the sea, naked bearded dragons reveal where vertebrates got their coats.

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Spookfish Have World's Strangest Eyes

bent nose spookfish

The four-eyed spookfish may have seemed strange enough. Now researchers say it doesn't really have four eyes. Instead, it is the known first vertebrate to use mirrors, rather than lenses, to focus light in its eyes.

“In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes — how to make an image — using a mirror," said Julian Partridge from the University of Bristol.

While the spookfish looks like it has four eyes, in fact it only has two, each of which is split into two connected parts. One half points upwards, giving the spookfish a view of the ocean — and potential food — above. The other half, which looks like a bump on the side of the fish's head, points down. These diverticular eyes, as they are called, are unique among all vertebrates in that they use a mirror to make the image, Partridge and colleagues found.

Very little light penetrates beneath about .62 miles (1,000 meters) of water. Like many other deep-sea fish, the spookfish is adapted to make the most of what little light there is. It is flashes of bioluminescent light from other animals that the spookfish are largely looking for. The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.

Although the spookfish was discovered 120 years ago, no one had discovered its reflective eyes until now because a live animal had never been caught.

When Professor Hans-Joachim Wagner from Tuebingen University caught a live specimen off the Pacific island of Tonga, members of his research team used flash photography to confirm the fish's upward and downward gazes.

Photographs looking down on the live fish produced eye-shine in the main tubular eyes that point upwards, but not in the diverticular eyes that point downward. Instead, these reflect light when seen from below.

It was when looking at sections of the eye that had been prepared for microscopy that Partridge realized that the diverticular mirrors where something exciting. The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack. This is not unique in the animal kingdom (it's why silvery fish are silvery) but the arrangement and orientation of the guanine crystals is precisely controlled such that they direct the light to a focus.

A computer simulation showed that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish's retina.

The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.

The research will be published this month in Current Biology .

  • How Your Eyes Work
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This fish has the world’s strangest eyes

Image: Spookfish

The four-eyed spookfish may have seemed strange enough. Now researchers say it doesn't really have four eyes. Instead, it is the first known vertebrate to use mirrors, rather than lenses, to focus light in its eyes.

“In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes — how to make an image — using a mirror," said Julian Partridge from the University of Bristol.

While the spookfish looks like it has four eyes, in fact it has only two, each of which is split into two connected parts. One half points upwards, giving the spookfish a view of the ocean — and potential food — above. The other half, which looks like a bump on the side of the fish's head, points down. These diverticular eyes, as they are called, are unique among all vertebrates in that they use mirrors to make the image, Partridge and colleagues found.

Very little light penetrates the ocean's waters below a depth of about a half-mile (1 kilometer). Like many other deep-sea fish , the spookfish is adapted to make the most of what little light there is. The spookfish largely looks for flashes of bioluminescent light from other animals . The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.

Although the spookfish was discovered 120 years ago, no one had discovered its reflective eyes until now because a live animal had never been caught.

When Professor Hans-Joachim Wagner from Tuebingen University caught a live specimen off the Pacific island of Tonga, members of his research team used flash photography to confirm the fish's upward and downward gazes.

Photographs looking down on the live fish produced eye-shine in the main tubular eyes that point upwards, but not in the diverticular eyes that point downward. Instead, these reflect light when seen from below.

It was when looking at sections of the eye that had been prepared for microscopy that Partridge realized that the diverticular mirrors were something exciting.

The mirror uses tiny reflective plates, probably consisting of guanine crystals, arranged into a multilayer stack. This is not unique in the animal kingdom (it's why silvery fish are silvery), but the arrangement and orientation of the guanine crystals is precisely controlled such that they direct the light to a focus.

A computer simulation showed that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish's retina.

The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.

The research will be published this month in Current Biology.

More on animal vision | deep-sea species

RNZ

Spookfish and Other Deep Sea Sharks

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By Alison Ballance

"They’re just so weird looking. When it was first suggested that I look at deep water sharks I was a little sceptical, because everyone wants to study your big typical pelagic species, the charismatic great whites and whale sharks. But spending a bit of time with them and just looking at them and all the weird features they have - there are some that glow in the dark, they have massive spines, and there’s lots we just don’t know about them so there’s lots of opportunity to learn." Brit Finucci , PhD student and deep sea shark scientist, Victoria University of Wellington

bent nose spookfish

Adult and juvenile Pacific spookfish (Rhinochimaera pacifica) photo Brit Finucci

bent nose spookfish

Beak-like grinding plates in mouth of a chimaera photo Alison Ballance

bent nose spookfish

Black ghostshark (Hydrolagus homonycteris) photo Brit Finucci

bent nose spookfish

Brit Finucci dissecting deep sea sharks photo Alison Ballance

bent nose spookfish

Brit Finucci holding a long nose spookfish and a brown chimaera photo Alison Ballance

bent nose spookfish

Brown chimaera (Chimaera carophila) photo Brit Finucci

bent nose spookfish

Brown chimaera (in front) and long nose spookfishes in the background photo Alison Ballance

bent nose spookfish

Chimaera egg cases photo Brit Finucc

bent nose spookfish

Pacific spookfish (Rhinochimaera pacifica) photo Brit Finucci

bent nose spookfish

Long nose spookfish (L) brown chimaera (centre) Pacific spookfish (R) photo Alison Ballance

bent nose spookfish

Owston’s dogfish (Centroscymnus owstonii) photo Brit Finucci

bent nose spookfish

Paired ovaries and uteruses in an immature female chimaera photo Alison Ballance

bent nose spookfish

Prickly dogfish (Oxynotus bruniensis) photo Brit Finucci

bent nose spookfish

Spiked claspers on male brown chimaera photo Alison Ballance

bent nose spookfish

Tenaculum (sex organ) on head of male Pacific spookfish (Rhinochimaera pacifica) photo Brit Finucci

bent nose spookfish

Tenaculum on male brown chimaera photo Alison Ballance

bent nose spookfish

Unidentified deep sea sharks photo Brit Finucci

 New Zealand deep sea sharks

Brit Finucci holding a long nose spookfish and a brown chimaera

Brit Finucci holding a long nose spookfish and a brown chimaera Photo: RNZ / Alison Ballance

Brit Finucci is a PhD student at Victoria University of Wellington, and she already knows more about six of New Zealand’s species of deep water sharks than almost anyone else in the world. She has spent many weeks this year dissecting more than 500 specimens of chimaeras that were accidentally caught by research boats working on the Chatham Rise and in the subantarctic, trying to find out as much as she can about these mysterious enigmatic creatures.

Chimaeras are ‘perhaps the oldest and most enigmatic groups of fishes alive today.’ Their closest living relatives are sharks, but they parted evolutionary ways about 400 million years ago. Chimaeras are deep sea sharks that are known by a number of different names, including spookfish, ratfish, rabbitfish, elephantfish and ghostsharks.

The name chimaera (or chimera) comes from Greek mythology, in which it was a fire-breathing monster composed of various animals: a lioness, a snake and a goat. 

Like sharks the skeletons of chimaeras are composed of cartilage, and the males have claspers for internal fertilization of females. Unlike true sharks, chimaeras have just a single pair of gills, and most species also have a mildly venomous spine located in front of the dorsal fin.

“They’re all characterised by having this big giant spine [on their back] which is probably a defensive mechanism,” says Brit.

As well as having flexible claspers with a spiked bulbous end, male chimaeras also have small sexual organs, which resemble a hooked club at the end of a stalk – known as tenaculum - on their forehead and in front of the pelvic fins.

Tenaculum (sex organ) on head of a male chimaera.

Tenaculum (sex organ) on head of a male chimaera. Photo: Brit Finucci

“It’s really odd with the chimaeras, males have this little organ on their head that’s the tenaculum,” says Brit. “When they’re mature the [tenaculum] get these tiny little hooks on them. They think it’s used to attach themselves to the female.”

Chimaeras are deep sea species. “Living in complete darkness at the bottom of the ocean they do have large eyes,” says Brit. “And they also have a tapetum, which is a reflective surface – you see that in cats, too, when you shine lights in their eyes and you get that reflection back.”

Not much is known about the diet of chimaeras. “Their teeth are more like rabbit teeth,” says Brit, “They have these tooth plates they use to grind their food.”

Beak-like grinding plates in mouth of a chimaera

Beak-like grinding plates in mouth of a chimaera Photo: RNZ / Alison Ballance

Sharks are a surprisingly diverse group of animals, ranging in size from the enormous whale shark, the world’s largest fish, to dwarf pygmy sharks (Squaliolus spp). Sharks, batoids (rays, skates and sawfish) and chimaeras form a distinctive group of cartilaginous fishes collectively referred to as the Chondrichthyans. There are more than 500 species of sharks , nearly 650 batoid species and 50 chimaera species, bringing the overall total of Chondrichthyans to about 1200 species.

Te Ara - the encyclopaedia of New Zealand says ‘in 2004 there were 70 known species of sharks, 26 skates and rays, and 12 chimaeras or ghost sharks in New Zealand … and at least four undescribed species.’

Prickly dogfish (Oxynotus bruniensis)

Prickly dogfish (Oxynotus bruniensis) Photo: Brit Finucci

Long nose spookfish (left), brown chimaera (centre), Pacific spookfish (right)

Long nose spookfish (left), brown chimaera (centre), Pacific spookfish (right) Photo: RNZ / Alison Ballance

Brit’s work is focusing on identifying when the six species she is looking at become mature, and she will look at stomach contents to see if she can work out what they’re eating. She is studying six different species:

The long nose spookfish ( Harriotta raleighana ) has a nose that can be up to half its body length. It belongs to a family of long-nosed chimaeras called Rhinochimaeridae , which has 8 known species in 3 genera.

The Pacific spookfish ( Rhinochimaera pacifica ) is another long-nosed chimaera.

The brown chimaera (Chimaera carophila) was only described as a distinct species in 2014. I t is only found in New Zealand, has a very blunt nose and large purple pectoral fins. There has been a resurgence in discovering and naming new shark species, both from existing specimens in museums and from new ones collected as more deep sea research is carried out. American taxonomist Dave Ebert alone has described 24 species, some of which he has found in Asian seafood markets.

The prickly dogfish ( Oxynotus bruniensis) has a thick body, a prominent hump back with two very large sail-like fins and a very rough skin.

The black ghostshark (Hydrolagus homonycteris) lives at depths of 500 to 1,400 metres.

Owston’s dogfish ( Centroscymnus owstonii ) grows to 1.2 metres long, and is caught as by-catch in the orange roughy and oreo fisheries.

  • environment
  • cartilaginous fish
  • deep sea sharks

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First vertebrate eye to use mirror instead of lens

By Jessica Griggs

24 December 2008

The deep sea is full of surprises, and the four-eyed spookfish is up there with the best of them. It is the first vertebrate found with eyes that use mirrors, rather than a lens, to focus light.

In clear water, sunlight can penetrate to a depth of 1000 metres, so some deep-sea fish have developed tubular, upward-looking eyes. “It is like having a telescope on your head that points towards the surface,” says Ron Douglas from City University London.

However, sunlight is only part of the story. The most important source of light at that depth is other creatures, as 80% emit their own light, called bioluminescence.

The unusual spookfish was caught in the deep waters between Samoa and New Zealand, but no one on the research boat knew what it was. “It caught my attention because it looked like it had four eyes, and vertebrates with four eyes don’t exist,” says Douglas.

It turns out that the spookfish ( Dolichopteryx longipes ) actually has just two eyes, but each eye has two parts, one looking upwards and the other down.

Getting reflective

The team found that the part looking down uses thousands of tiny reflective crystals – acting like mirrors – that are angled in slightly different directions to focus light onto the retina. This is completely different to a typical fish eye, which uses a single lens to bend light onto a focal point, similar to the way the human eye works.

Other tubular-eyed fish do use optical techniques to look sideways and downwards but these mechanisms have no way to focus light into a clear image.

The spookfish is the only deep-sea fish with eyes that have been shown to produce a focused image when looking both up and down. “This is the first demonstration that vertebrates are not as optically boring as we thought,” says Douglas.

Mike Land from the University of Sussex, UK, thinks the eye is “intriguing” and could be unique to the spookfish. “I doubt we’ll see this in other vertebrates – surely we would have discovered it by now.”

Journal reference: Current Biology , DOI: 10.1016/j.cub.2008.11.061

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Spookfish Uses Mirrors For Eyes

A remarkable new discovery shows the four-eyed spookfish to be the first vertebrate ever found to use mirrors, rather than lenses, to focus light in its eyes.

Professor Julian Partridge from the University of Bristol, said: “In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes – how to make an image – using a mirror.”

While the spook fish looks like it has four eyes, in fact it only has two, each of which is split into two connected parts. One half points upwards, giving the spookfish a view of the ocean – and potential food – above. The other half, which looks like a bump on the side of the fish’s head, points downwards into the abyss below. These ‘diverticular’ eyes are unique among all vertebrates in that they use a mirror to make the image.

Very little light penetrates beneath about 1000m of water and like many other deep-sea fish the spookfish is adapted to make the most of what little light there is. At these depths it is flashes of bioluminescent light from other animals that the spookfish are largely looking for.  The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.

Although the spookfish was first discovered 120 years ago, no one had discovered its reflective eyes until now because a live animal had never been caught. When Professor Hans-Joachim Wagner from Tuebingen University caught a live specimen off the Pacific island of Tonga, members of his research team used flash photography to confirm the fish’s upward and downward gazes.

Photographs taken by Dr Tammy Frank looking down on the live fish produced eye-shine in the main tubular eyes that point upwards, but not in the diverticular eyes that point downward.  Instead, these reflect light when seen from below.

It was when looking at sections of the eye that had been prepared for microscopy that Professor Partridge realised that the diverticular mirrors where something exciting. The mirror uses tiny plates, probably of guanine crystals, arranged into a multi-layer stack. This is not unique in the animal kingdom (it’s why silvery fish are silvery) but the arrangement and orientation of the guanine crystals is precisely controlled such that they direct the light to a focus. Partridge’s computer simulation showed that the precise orientation of the plates within the mirror's curved surface is perfect for focusing reflected light onto the fish’s retina.

The use of a single mirror has a distinct advantage over a lens in its potential to produce bright, high-contrast images. That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.

The research will be published this month in Current Biology.

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Text by Victoria Zavyalova. Edited by Joe Crescente, Alastair Gill. Design and layout by Victoria Zavyalova. Images credits: Aeroflot press service, Ruslan Fayzulin / Russia Beyond The Headlines. © 2015 All Right Reserved. Russia Beyond The Headlines [email protected]

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COMMENTS

  1. Brownsnout spookfish

    The brownsnout spookfish or brown-snout spookfish ( Dolichopteryx longipes) is a species of barreleye in the family Opisthoproctidae. [1] [2] [3] It and the glasshead barreleye fish are the only vertebrates known to employ a mirror, in addition to a lens, to focus an image in its eyes.

  2. Spookfish have odd eyes, not just odd name

    Science — Spookfish have odd eyes, not just odd name A deep sea creature known as the Brownsnout spookfish has been found to be the … Matt Ford - Jan 9, 2009 2:24 pm UTC

  3. Rhinochimaera pacifica

    Rhinochimaera pacifica, commonly known as the Pacific spookfish, knifenose chimaera, narrownose chimaera, Pacific long-nosed chimaera, or Pinocchiofish, is a species of chimaera in the family Rhinochimaeridae. [2] It lives in various parts of the Pacific Ocean and can be characterized by its long snout. Description

  4. Spookfish

    Category: Animals & Nature Related Topics: barreleye Argentinoidei See all related content → spookfish, any of about 11 species of small marine fishes constituting the family Opisthoproctidae (order Salmoniformes), with representatives in each of the major oceans.

  5. National Marine Sanctuary Foundation

    Barreleye fish (Macropinna microstoma), also known as spookfish, are one of those deep-sea species that looks otherworldly. They've got transparent heads that reveal their eyes, brains, and other organs, making them a fascination of ocean scientists for generations.

  6. Built-In Mirrors Help Spookfish See in the Dark Ocean Depths

    The odd-looking spookfish is the only vertebrate known to have mirrors in its eyes, according to a new report. The mirrors gather and focus light better than lenses, which spookfish also have, and appear to be an adaptation for living in the murky depths of the Pacific Ocean. Scientists discovered the spookfish's unusual anatomy after examining ...

  7. WATCH: Deep-Sea Spookfish Is One of The World's Most ...

    This spookfish belongs to the family Rhinochimaeridae, commonly known as long-nosed chimaeras. Their characteristic elongated snouts can be conical or paddle-shaped, and they're covered in a series of sensory nerve endings to help them track down prey.

  8. Brownsnout spookfish

    The brownsnout spookfish or brown-snout spookfish is a species of barreleye in the family Opisthoproctidae. It and the glasshead barreleye fish are the only vertebrates known to employ a mirror, in addition 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 ...

  9. Pacific Spookfish, Rhinochimaera pacifica (Mitsukuri, 1895)

    Pacific Spookfish, Rhinochimaera pacifica (Mitsukuri, 1895) - The Australian Museum. Goldspotted Sweetlips, Plectorhinchus flavomaculatus (Ehrenberg, 1830) Sailfin Tang, Zebrasoma veliferum (Bloch, 1795) Imperador, Beryx decadactylus Cuvier, 1829. Leaf Scorpionfish, Taenianotus triacanthus Lacépède, 1802.

  10. 'Spookfish' has mirrors for eyes

    Spookfish is a name often given to Barreleyes - a group of small, odd-looking deep-sea fish species, found in tropical-to-temperate waters of the Atlantic, Pacific, and Indian Oceans. A rare live brownsnout spookfish, Dolichopteryx longipes , was caught last year between New Zealand and Samoa, by Professor Hans-Joachim Wagner, of Tuebingen ...

  11. The Fish That Cracked the Mystery of Mirror Vision

    The brownsnout spookfish's downward facing eye (1) focuses light on the retina (a) using a mirror made of reflective crystals (b). The main eye (2) more conventionally uses a lens (c) to focus light on its retina (d).

  12. Spookfish Uses Mirrors for Eyes

    The spookfish is the first vertebrate discovered to use mirrors for eyes. Instead of using lenses to focus light and create images, the spookfish utilizes reflective mirrors. At first glance, the ...

  13. Spookfish eye uses mirrors instead of a lens

    The fact that the spookfish is a back-boned animal - a vertebrate - makes its eye that much more special. Inverterbrates have a wide variety of eye designs, but vertebrates, from fish to humans,...

  14. Spookfish Have World's Strangest Eyes

    Fish Spookfish Have World's Strangest Eyes News By Live Science Staff published 8 January 2009 View of a spookfish from above. Inset shows a section through the diverticulum eye showing the way...

  15. This fish has the world's strangest eyes

    Scientists say the spookfish is first known vertebrate to use mirrors, rather than lenses, to focus light in its eyes.

  16. Spookfish and Other Deep Sea Sharks

    The long nose spookfish (Harriotta raleighana) has a nose that can be up to half its body length. It belongs to a family of long-nosed chimaeras called Rhinochimaeridae, which has 8 known species in 3 genera. The Pacific spookfish (Rhinochimaera pacifica) is another long-nosed chimaera.

  17. First vertebrate eye to use mirror instead of lens

    24 December 2008. The deep sea is full of surprises, and the four-eyed spookfish is up there with the best of them. It is the first vertebrate found with eyes that use mirrors, rather than a lens ...

  18. Spookfish Uses Mirrors For Eyes

    A remarkable new discovery shows the four-eyed spookfish to be the first vertebrate ever found to use mirrors, rather than lenses, to focus light in its eyes. Professor Julian Partridge from the ...

  19. Never Forget a Deep-Sea Fish Exists That Looks Just Like Tim Burton

    This spookfish belongs to the family Rhinochimaeridae, commonly known as long-nosed chimaeras. Their characteristic elongated snouts can be conical or paddle-shaped, and they're covered in a series of sensory nerve endings to help them track down prey (no Tim Burton-style glowing red nose that we know of though, sorry).

  20. Tasty Peach Moscow Mule Recipe

    Peach vodka is what primarily gives this Peach Moscow Mule its peach flavor. However, if you don't want to buy peach vodka or simply want a stronger peach flavor, you could one of two things: Muddle 1/3 cup chopped peaches or 1/2 of a peach at the bottom of the mug as the first step, OR. Puree 1/3 cup chopped peaches or 1/2 of a peach in a blender.

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    Country of origin: Russia Location: Elektrostal, Moscow Oblast / Saint Petersburg Status: Active Formed in: 2013 Genre: Brutal Death Metal/Goregrind Themes: