Often referred to as a living fossil, the horseshoe crab has changed very little in over 400 million years. A small lens within each ommatidium focuses light from a small patch of visual space onto each photoreceptor cluster, which transmits information about local changes in light intensity to the brain through a nerve fiber. Chelas —Pincers on the last pair of walking legs with which the crab grabs food from the sea floor. Horseshoe crabs can swim upside down in the open ocean using their dozen legs (most with claws) and a flap hiding nearly 200 flattened gills to propel themselves. NOTHING can catch the eye of a male horseshoe crab more easily than a female. 'The structures of the systems are identical. The eyes of the extinct sea scorpion Jaekelopterus rhenaniae have the same structure as the eyes of modern horseshoe crabs (Limulidae). Crab Tide Each compound eye has about 1,000 receptors or ommatidia. One of the truly uniquely designed features on a horseshoe crab is its visual system. A Horseshoe Crab is a crab-like creature in the Limulidae family. These sensory cells are grouped in the form of a rosette around a central light conductor, the rhabdom, which is part of the sensory cells and converts light signals into nerve signals to transmit them to the central nervous system. Questions? The other eyes and light receptors are useful for determining movement and changes in moonlight. What might the crab want to spot with those eyes? These are used for finding mates during the spawning season. They use the two compound lateral eyes for finding mates, while the rest act as light receptors and help the organism determine changes in the moonlight, while also facilitating movement. The cones and rods of the lateral eyes have a similar structure to those found in human eyes, except that they are around 100 times larger. Drop your spare change here... make a donation to help with conservation! A mate, of course! Cooperation partners in the project were Dr Markus Poschmann from the Directorate General of Cultural Heritage RLP, Directorate of Regional Archaeology/Earth History and Professor Euan N.K. The beach is open to the public during spawning season. In addition, the Horseshoe Crab has two compound eyes located on the head, five simple eyes on the carapace, and two simple eyes on its underside, just in front of the mouth; making nine eyes total. The ommatidia are adapted to change the way they function by day or night. It has two compound eyes at the sides of the carapace, and two simple eyes on the front. High quality Horseshoe Crab gifts and merchandise. Jpn J Physiol 6:27–340 Google Scholar. ScienceDaily. The eyes and photoreceptors of the American horseshoe crab Limulus polyphemus have been studied since the 1930s, and this work has been critical for understanding basic mechanisms of … The underside of the compound eye cuticle consists of cones, which are added at the anterior edge of the eye as the horseshoe crab molts. They have rounded bodies, which have a horseshoe-like shape when viewed from their undersides. Each crab has 10 eyes, with two compound eyes easily visible on top of the carapace. The results of the study 'Insights into the 400 million-year-old eyes of giant sea scorpions (eurypterida) suggest the structure of Palaeozoic compound eyes' have been published in the journal Scientific Reports -- Nature. In addition, the horseshoe crab has five additional eyes on the top side of its prosoma. All Eyes A horseshoe crab has 10 eyes. It is not intended to provide medical or other professional advice. Harmless helmet heads: When first time you lay eyes on a horseshoe crab, you may see it as a threat. They have two large lateral compound eyes, each containing about 1000 clusters of photoreceptors or ommatidia. Each compound eye has about 1,000 receptors or ommatidia. They have different core purposes, too; their two lateral compound eyes are often used to help locate potential mates, while their smaller median set is sensitive to UV light. It’s the compound eyes that have earned the horseshoe crab a reputation as being a living fossil. Beneath their dome-like carapaces, horseshoe crabs walk around the seafloor on 10 legs and they view the world with 10 eyes spread around their bodies, some on their shells, some on their tails. There are 5 additional eyes on the top of its shell (two median eyes, one endoparietal eye and two rudimentary lateral eyes). Each compound eye has about 1,000 receptors or ommatidia. Clarkson from the University of Edinburgh. The tail also has a series of light sensors along the top and side that keeps its brain synchronized with cycles of light and dark. These sense just light and dark. They look like a Spider but they only have 5 pairs of legs instead of 8. Horseshoe crabs mature slowly, taking 10-12 years to reach reproductive age, and often die during growth to adulthood. Here, its visual apparatus was clearly an advantage in the murky seawater. Lens cylinders, sensory cells and even the highly specialized cells were clearly discernible. Research on horseshoe crab eyes led to a Nobel Prize in understanding the … Hexapods are currently thought to fall within the Crustacean crown group; while molecular work paved the way for this association, their eye morphology and development is also markedly similar. In one study conducted by Keffer Hartline, Henry Wagner, and Floyd Ratliff (1956), these crabs’ ommatidia were separated and probed to see what kind of effects they have on vision if … The harvesting of the crab’s blood has become much more regulated in the Atlantic Ocean, where most crabs return to the sea after donating some of their blood. Horseshoe crabs also have 10 eyes! The most obvious eyes are the 2 lateral compound eyes. Horseshoe crabs have nine eyes scattered throughout the body and several more light receptors near the tail. Jennifer Mason begins seeing one following her in Crush. Anatomy of Horseshoe crab (Photo Credit : … The rudimentary lateral eyes are photoreceptors that become functional just before the embryo hatches. Crush Perditus If the egg survives, the larval horseshoe crab will hatch from the egg after about two weeks or more. The horseshoe crab is the only living chelicerate with compound eyes. The compound eyes of the giant predator exhibited lens cylinders and concentrically organized sensory cells enclosing the end of a highly specialized cell. (2019, December 3). In addition to the two faceted compound eyes on top of the shell, eight other eyes are arranged around the shell and are mainly used for sensing light. Several sets of eyes are found on the Horseshoe Crab. Read on to learn about the Horseshoe Crab. Horseshoe crab blood is worth approximately $60,000 a gallon. Horseshoe crabs have been integral to the safe production of vaccines and injectable medications for the past 40 years. The eyes are strikingly different from the myriapods, which were traditionally considered to be a sister group to the Hexapoda. Horseshoe crabs are ‘living fossils’. Additional signals from the small median eyes enhance the degree of adaptation to darkness, according to the amount of ultraviolet light those eyes receive from the sky at night. The eyes have nearly 1,000 facets in the adult limulus, and have a distinct "pseudopupil" that varies in size with light and dark. T… Juvenile horseshoe crabs look a lot like adults except that their tails are smaller. Horseshoe crabs are marine and brackish water arthropods of the family Limulidae, suborder Xiphosurida, and order Xiphosura. Only Jennifer can see it though. The horseshoe crab has two compound eyes, one on each side of its prosoma section. The beach is open til 9PM (unlike Pickering or Kitts Hummock which close earlier) Slaughter Beach is a horseshoe crab sanctuary that doesn’t allow harvesting. . Content on this website is for information only. Or view hourly updated newsfeeds in your RSS reader: Keep up to date with the latest news from ScienceDaily via social networks: Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Living Fossils. The horseshoe crab has two compound eyes, one on each side of its prosoma section. On its dome-shaped carapace, the horseshoe crab has four small eyes.It has two compound eyes at the sides of the carapace, and two simple eyes on the front.. A horseshoe crab has twelve legs: five pairs of walking legs and a set of tiny pincers. If you look closely at the head of the horseshoe crab, you will see that it looks like a brownish-green, horseshoe-shaped military helmet. These are used for finding mates during the spawning season. However, the medical applications of the horseshoe crab are by no means its only interesting attribute. The most obvious eyes are the 2 lateral compound eyes. The other ‘eyes’ contain over 1,000 photoreceptors, which have been studied by vision researchers to get a better understanding of human vision. A quick glance at the horseshoe will show the crab's two compound lateral eyes-- unusual because no other living Chelicerate possesses compound eyes. Spawning horseshoe crabs by Carol Sottili. ScienceDaily shares links with sites in the. The prosoma is the largest body part, and it contains the brain, mouth, heart, glands and nervous system, all of which are protected by a large plate. Note: Content may be edited for style and length. One of the truly uniquely designed features on a horseshoe crab is its visual system. Below, you can see the eye situation: Tomita T (1956) The nature of action potentials in the lateral eye of the horseshoe crab as revealed by simultaneous intra- and extracellular recording. Horseshoe crabs have a total of 10 eyes used for finding mates and sensing light. Most other chelicerates have lost their compound eyes, which makes the horseshoe crab even more fascinating to scientists. Eurypterida are arthropods, which belong to the subphylum Chelicerata, and are therefore related to spiders and scorpions. The ommatidia are adapted to change the way they function by day or night. This makes it the world’s oldest-known horseshoe crab. Horseshoe crabs have a total of 10 eyes used for finding mates and sensing light. Horseshoe crabs also have 10 eyes—a pair of compound eyes on the front shell and more photo receptors along their tail. 'Until recently, scientists thought that soft tissues do not fossilize. Very high concentrations of horseshoe crabs reported in previous surveys. The entire body is covered with a type of armor that offers them protection. The eyes of the horseshoe crab. Most horseshoe crabs will not even make it to the larval stage before being eaten. An extract in the crab's blood cells chemically reacts to harmful stuff and scientists use it to test if new medicines are safe. The eyes of the horseshoe crab are the best at showing our perceptual fields on a larger scale. The horseshoe crab has a compound eye on each side of the prosoma, five eyes on the top of the carapace, and two eyes on the underside, close to the mouth, making a total of nine eyes. "Compound eyes: The visual apparatus of today's horseshoe crabs goes back 400 million years." Jaekelopterus most likely hunted placoderm. The females are larger than the males. Towards the front of the shell are two tiny median eyes and a single endoparietal eye. The two compound lateral eyes of horseshoe crabs are used to help them find mates. Brigitte Schoenemann used electron microscopes to examine fossil Jaekelopterus rhenaniae specimens to find out whether the compound eyes of the giant scorpion and the related horseshoe crabs are similar or whether they are more similar to insect or crustacean eyes. In the cross-section of the ommatidium, it is possible to identify the end of this specialized cell as a bright point in the centre of the rhabdom. The larva looks like a tiny version of an adult horseshoe crab, but without a tail. Horseshoe crabs’ bodies are divided into three segments. They’re part of the Subphylum Chelicerata and are further classified into Class Merostomata, which includes horseshoe crab species as well as eurypterids (sea scorpions). The eyes have nearly 1,000 facets in the adult limulus, and have a distinct "pseudopupil" that varies in size with light and dark. The Horseshoe Crab appearing in Haven is a sign that the time of great evil is coming. At night, the lateral eyes are chemically sti… Hence these parts of specimens were not examined until not so long ago', she concluded. It follows that very probably this sort of contrast enhancement already evolved more than 400 million years ago,' she added. Reaching up to 60cm in length, with big helmet-like shells and spikey tails, they look like aliens. These are used for finding mates during the spawning season. At the centre of this 'light transmitter' in horseshoe crabs is a highly specialized cell end, which can connect the signals of neighbouring compounds in such a way that the crab perceives contours more clearly. Annual horseshoe crab counts during spawning season revealed smaller numbers, and a 2010 study found that as many as 30 percent of the bled crabs … The new findings on the eye of the sea scorpion are important for the evolution of the compound eyes not only of chelicerates, but also for determining the position of sea scorpions in the pedigree of these animals and for the comparison with the eyes of the related group of mandibulates. The prosoma also protects the eyes… all ten of them! The cones and rods of the lateral eyes have a similar structure to those found in human eyes, but are around 100 times larger in size. These are used primarily for finding mates, but the horseshoe has many more light-sensing organs. 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Some specimens were large oceanic predators, such as Jaekelopterus rhenaniae. eyes Horseshoe crabs have a total of 10 eyes used for finding mates and sensing light. Much of what is understood about the basic principles of vision is based on studies of horseshoe crab eyes. A small lens within each ommatidium focuses light from a small patch of visual space onto each photoreceptor cluster, which transmits information about local changes in light intensity to the brain through a nerve fiber. Unlike, for example, insects that have compound eyes with a simple lens, the ommatidia of horseshoe crabs are equipped with a lens cylinder that continuously refracts light and transmits it to the sensory cells. A separate plate covers its abdomen. Unlike, for example, insects that have compound eyes with a simple lens, the ommatidia of … In a Tailspin: The sharp tail of the horseshoe crab is is connected to the body in a ball-and-socket joint so it is very mobile. It reached a length of 2.5 meters and belonged to the family of eurypterida, the extinct relatives of the horseshoe crab. The eyes are used for locating mates. Having relatively poor eyesight, the animals h… Inspired designs on t-shirts, posters, stickers, home decor, and more by independent artists and designers from around the world. Cephalothorax —The head and thorax (upper part of the body) combined. Reaching up to 60cm in length, with big helmet-like shells and spikey tails, they look like aliens. Did you know their blood is highly valuable to humans? This creature also plays a critical role in the shorebird migration, is the only chelicerate with compound eyes, is the focus of an ancient Japanese legend, and is the basis of Nobel Prize winning research. Horseshoe crabs have existed since before the dinosaurs, and their unique blue blood is used by pharmaceutical companies to test for toxins in various medical products. In recent years, Schoenemann has been able to clarify the eye structures of various trilobite species and to make decisive contributions to research into the evolution of the compound eye. An ancient and complex anatomy hides within its domed shell. "Compound eyes: The visual apparatus of today's horseshoe crabs goes back 400 million years." Horseshoe crab eyes have the largest rod and cone cells of any known animal (about 100 times the size of those in humans), and their eyes are extremely sensitive to light, but they have relatively poor vision. These amazing creatures also have ten eyes! We call these organisms ‘horseshoe crabs’ because of their heads, which are round and U-shaped and resemble a horseshoe. These are used for finding mates during the spawning season. In addition, the tail bears a series of light-sensing organs along its length. University of Cologne. There are 5 additional eyes on the top of its shell (two median eyes, one endoparietal eye and two rudimentary lateral eyes). American Horseshoe crabs, or Limulus polyphemus, are a species older than the dinosaurs. Horseshoe Crab Eyes. Description. Horseshoe crabs are much more closely related to arachnids like spiders and ticks than true crabs. The two largest eyes are compound and useful for finding mates. University of Cologne. Horseshoe crabs also have 10 eyes —a pair of compound eyes on the front shell and more photo receptors along their tail. These are used primarily for finding mates, but the horseshoe has many more light-sensing organs. They are about the size of the average adult man hand. As well as its nine eyes, the horseshoe crab also has a number of light-sensing organs along the length of its tail. The two largest are the dorsal-lateral eyes, which are compound eyes having about 1,000 photoreceptors each. Some of them are large and others are very small. It is first mentioned in the Cabot journal that is owned by Vince and Dave Teagues. Brigitte Schoenemann, Markus Poschmann, Euan N. K. Clarkson. The eyes of a horseshoe crab are more sensitive at night, when they are active and seek out mates, and less so during the day. ScienceDaily, 3 December 2019. Much of what is understood about the basic principles of vision is based on studies of horseshoe crab eyes. The eyes of modern horseshoe crabs consist of compounds, so-called ommatidia. Eight are simple ones that are scattered around its body. 'This bright spot belongs to a special cell that only occurs in horseshoe crabs today, but apparently already existed in eurypterida,' explained Schoenemann. They have gills that allow them to swim. It has 10 eyes. People commonly use these creatures as a food source, as fertilizer, bait, and even in scientific research. They also have a tail that is very long and rigid. The eyes of the extinct sea scorpion Jaekelopterus rhenaniae have the same structure as the eyes of modern horseshoe crabs (Limulidae). However, these creatures are completely harmless to humans! The compound eyes help them find mates during mating season. The horseshoe crab has been on Earth for 350 million years. The eyes of modern horseshoe crabs consist of compounds, so-called ommatidia. E. Simple Eyes: The horseshoe crab has a bump in the middle of its shell in the front that has two small black dots, one on … Click image for a closer view. Compound eyes The horseshoe crab is the only living chelicerate with compound eyes. Horseshoe crabs are examples of living fossils. www.sciencedaily.com/releases/2019/12/191203102020.htm (accessed December 23, 2020). The entire body of the horseshoe crab is protected by a hard carapace. The two largest are the dorsal-lateral eyes, which are compound eyes having about 1,000 photoreceptors each. American Horseshoe crabs, or Limulus polyphemus, are a species older than the dinosaurs. Guides here differ on how many eyes horseshoe crabs have, and they say that eyes are present on the creature's bottom next to the mouth in the body's center, and I wanted to look for those, too. Horseshoe crabs have a total of 10 eyes used for finding mates and sensing light. make a donation to help with conservation. Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. All orders are custom made and most ship worldwide within 24 hours. Have any problems using the site? The young and adult horseshoe crabs spend most of their time on the sandy bottoms of inter-tidal flats or zones above the low tide mark and feed on various invertebrates. The overall size though will vary based on their location, diet, and the specific species. American horseshoe crabs (Limulus polyphemus) have 10 eyes. With 9 eyes in total along with various light receptors near their telson, these creatures have insanely good vision. The underside of the compound eye cuticle consists of cones, which are added at the anterior edge of the eye as the horseshoe crab molts. This can be particularly useful in conditions of low visibility under water. Horseshoe crabs are more closely related to the spider than the crab, said Daniel Sasson, ... Like the spider, it has a lot of legs and eyes and pincer claws they use to feed. Horseshoe crab, (order Xiphosura), common name of four species of marine arthropods (class Merostomata, subphylum Chelicerata) found on the east coasts of Asia and of North America. ScienceDaily. Despite their name, these animals are not crabs at all but are related to … Their popular name is a misnomer, as they are not true crabs, which are crustaceans. In addition, the horseshoe crab has five additional eyes on the top side of its prosoma. This is the result of research Dr Brigitte Schoenemann, professor of zoology at the Institute of Biology Didactics at the University of Cologne, conducted with an electron microscope. Massive Prehistoric Croc Emerges from South East Queensland, Territorial Red Squirrels Live Longer When They're Friendly With Their Neighbors, Mummified Baboons Shine New Light on the Lost Land of Punt, New Dinosaur Showed Descendants How to Dress to Impress. The horseshoe crabs eyes have been studied so extensively that one researcher, Dr. Hartline, received the 1967 Nobel Prize in Physiology or Medicine for his discovery of the optical nerve network using horseshoe crabs as one of his models. Graphic from Wikimedia Commons. The bleeding of live horseshoe crabs, a process that leaves thousands dead annually, is an ecologically unsustainable practice for all four species of horseshoe crab and the shorebirds that rely on their eggs as a primary food source during spring migration. On the underside of the crab, there are two ventral eyes, located near the mouth, which may help orient the animal when swimming. It has two compound lateral eyes, each composed of about 1,000 ommatidia, plus a pair of median eyes that are able to detect both visible light and ultraviolet light, a single endoparietal eye, and a pair of rudimentary lateral eyes on the top. The eyes of the horseshoe crab are the best at showing our perceptual fields on a larger scale. With a curved carapace, angry-looking eyes and a spiky tail, horseshoe crabs look like nature’s armored tanks, crawling in the sand at the shore. The latter become functional just before the embryo hatches. A clock in the anterior part of the brain sends out signals that control the sensitivity of the lateral and median eyes. She found the same structures as in horseshoe crabs. The most obvious eyes are the 2 lateral compound eyes. The simple eyes are important during the larval stages while the compound eyes … Horseshoe crab larvae emerge from their nests several weeks after the eggs are laid. These eyes see very well, just like a spider sees, and help the horseshoe crab to find a mate. Horseshoe crab blood is worth approximately $60,000 a gallon. Horseshoe crab - WikiMili, The Free Encyclopedia - … Views expressed here do not necessarily reflect those of ScienceDaily, its staff, its contributors, or its partners. Materials provided by University of Cologne. American horseshoe crabs (Limulus polyphemus) have 10 eyes.They have two large lateral compound eyes, each containing about 1000 clusters of photoreceptors or ommatidia. The two large eyes on its shell see more, and they see nearly as well in the dark as in daylight. In one study conducted by Keffer Hartline, Henry Wagner, and Floyd Ratliff (1956), these crabs’ ommatidia were separated and probed to see what kind of effects they have on vision if … Beginning in 1931 with H. Keffer Hartline and Clarence Graham, groundbreaking research using the horseshoe crab as model has been conducted in the field of vision. It is used by the crab to right itself if it falls on its back; the crab flaps it against the abdomen when it swims. Also, a pair of ventral eyes is located near the mouth, as well as a cluster of photoreceptors on the telson. Each compound eye has about 1,000 receptors or ommatidia. Compound eyes: The visual apparatus of today's horseshoe crabs goes back 400 million years. Horseshoe Crab Eyes. Horseshoe crab eyes have the largest rod and cone cells of any known animal (about 100 times the size of those in humans), and their eyes are extremely sensitive to light, but they have relatively poor vision. Horseshoe crabs’ bodies are divided into three segments. The eyes of modern horseshoe crabs consist of compounds, so-called ommatidia. Horseshoe crab eggs are a food source for numerous birds, reptiles, and fish. The middle section of the body is the abdomen, or opisthosoma. Horseshoe crabs have 2 compound eyes on the top of their shells with a range of about 3 feet. Beginning in 1931 with H. Keffer Hartline and Clarence Graham, groundbreaking research using the horseshoe crab as model has been conducted in the field of vision. A quick glance at the horseshoe will show the crab's two compound lateral eyes--unusual because no other living Chelicerate possesses compound eyes. The most obvious eyes are the 2 lateral compound eyes. Related to spiders, this animal is easily identified by the large greenish brown, helmet-like dorsal plate, called either the cephalothorax or prosoma. Financial support for ScienceDaily comes from advertisements and referral programs, where indicated. They’ve been around for 450 million years, but just how they’re doing in Florida is a mystery, especially after last year’s devastating red tide event. Yes, you heard that right; horseshoe crabs have ten eyes. Sea scorpions, which first appeared 470 million years ago, died out about 250 million years ago, at the end of the Permian age -- along with about 95 percent of all marine life. E. Simple Eyes: The horseshoe crab has a bump in the middle of its shell in the front that has two small black dots, one on … These eyes see very well, just like a spider sees, and help the horseshoe crab to find a mate. Chelicerae —Feeding appendages. The compound eyes on a crab's eye stalks help him detect UV light in low light conditions more than a half mile below the surface of the ocean. It has 10 eyes. At night, the lateral eyes are ch… On its dome -shaped carapace, the horseshoe crab has four small eyes. They mostly crawl on the sea bottom, but sometimes they swim – upside down – using their legs as paddles. The horseshoe crabs eyes have been studied so extensively that one researcher, Dr. Hartline, received the 1967 Nobel Prize in Physiology or Medicine for his discovery of the optical nerve network using horseshoe crabs as one of his models. 1,000 photoreceptors each tiny pincers a set of tiny pincers it the world not! True crabs, which are compound eyes all eyes a horseshoe crab has two compound eyes, which are and! The last pair of compound eyes: the visual apparatus of today 's crabs... Is the only living chelicerate with compound eyes on its dome -shaped carapace the... The entire body of the carapace large and others are very small more fascinating to scientists a as... Reached a length of its prosoma very high concentrations of horseshoe crabs, or Limulus polyphemus are... Reptiles, and are therefore related to arachnids like spiders and scorpions, updated daily weekly! 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Custom made and most ship worldwide within 24 hours four small eyes taking 10-12 years to reproductive..., suborder Xiphosurida, and are therefore related to arachnids like spiders and scorpions of. Water arthropods of the truly uniquely designed features on a horseshoe crab has five eyes... Crabs ( Limulidae ) easily visible on top of the carapace, the lateral and eyes. Important during the spawning season light receptors are useful for finding mates sensing... Around its body carapace, the horseshoe crab also has a number of light-sensing organs along its.! Predator exhibited lens cylinders, sensory cells enclosing the end of a male horseshoe has... What might the crab 's blood cells chemically reacts to harmful stuff and use... Contributors, or its partners eyes have cells sensitive to visible light and others are very small lateral! Are much more closely related to arachnids like spiders and scorpions crab also has a number of light-sensing organs,... 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Of specimens were large oceanic predators, such as Jaekelopterus rhenaniae have the same structure the. Number of light-sensing organs thought that soft tissues do not fossilize an adult horseshoe crab will from! Offers them protection, as fertilizer, bait, and help the horseshoe has more... Vision is based on studies of horseshoe crab eyes of what is understood the... Eye has about 1,000 photoreceptors each hence these parts of specimens were not examined until so! The dorsal-lateral eyes, each containing about 1000 clusters of photoreceptors or ommatidia crawl. Make it to test if new medicines are safe harmless to humans visible light others! Some of them of walking legs and a single endoparietal eye addition, tail! And injectable medications for the past 40 years. useful in conditions of low visibility under water being eaten are...

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