Narrow-Mouthed Frogs: Microhylidae

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With 362 species, this large family of narrow-mouthed frogs comes in many shapes and sizes. Most species are brown, tan, or yellow-brown on their backs, sometimes with brighter colors on their undersides. The horned land frog, for example, has a brown back and gray sides, but may have an orange or red underside. The saffron-bellied frog has a black back with yellowish to silvery flecks, and large, bright yellow spots on its black sides and belly. Some, like the rubber frog, stand out even more. The rubber frog has a dark brown to black body with pink or red markings on its back.

Many, but not all, of the narrow-mouthed frog species have a round, wide, often chubby-looking body and a short head that ends in a narrow or pointed snout. This gives these species an overall shape that resembles a pear or a teardrop. Others do not have this body shape. Some are long and thin, and others have rounded bodies with fairly wide heads. The New Guinea bush frog, for example, has a head that is just as wide as its body. Rain frogs of the genus Breviceps are also plump and round. They have such tiny legs that they cannot hop, and walk instead. Another rather plump frog, known as the ornate narrow-mouthed frog, has longer legs than Breviceps and is an excellent hopper.

Many, but not all, of the narrow-mouthed frogs have noticeable, small warts on their backs and legs. The typical member of this family has little or no webbing on its toes. Many have pads on their toe tips. The horned land frog, for instance, has large pads, especially on the toes of its front legs. The eyes of species in this family are frequently small, but some, like Boulenger's callulops frog, have large eyes. A few, including the New Guinea bush frog and the horned land frog, have eyelids decorated with small spines that almost look like thick eyelashes.

The majority of the frogs in this family share a few somewhat hidden characteristics. Unlike other frogs, most species of narrow-mouthed frogs have two or three zigzag folds on the roof of the mouth. The roof of the mouth is called the palate (PAL-ett). The majority of the species in this family also have no teeth. In addition, most narrow-mouthed frogs have smaller bones in the shoulder and chest than other frogs typically have. Some, like the Malaysian painted frog, have no neck bones and, therefore, no neck. In this case, the head almost blends in with the body, which makes the frog look quite chubby. In fact, the nickname of the Malaysian painted frog is chubby frog.

The typical narrow-mouthed frog grows to 1.6 inches (4 centimeters) long from snout to rump, and some never even reach 0.5 inches (1.3 centimeters) long as adults. The largest species, like the Malaysian painted frog, can top 3 inches (7.5 centimeters) long, and some can reach 4 inches (10 centimeters) in length. In most species of narrow-mouthed frogs, females are at least a little larger than the males. In some cases, like Bushveld's rain frog, the female is almost twice the size of the male.


Depending on the species, narrow-mouthed frogs may live in southern North America, central and northern South America, Central America, southern Africa and Madagascar, southeast Asia including the Philippines and the East Indies, and/or northern Australia and New Guinea.


The members of this family live in many different habitats. Most prefer hot and humid rainforests, where many live in underground burrows. Some live along but above the ground, and others spend at least part—and sometimes all—of their lives in the trees. A few species, like those with the scientific genus names of Oreophryne and Oxydactyla, live high in the mountain grasslands of New Guinea. The rain frogs of southern Africa, on the other hand, survive the dry, almost desert-like sand dunes by spending much of their time in underground burrows. These odd frogs, with their exceptionally plump bodies and four tiny legs, will venture out of their burrows during the rain or on humid nights.


Most narrow-mouthed frogs eat only small invertebrates (in-VER-teh-brehts), which are insects and other animals without backbones. Many species have small mouths that come to a point at the end and can only eat tiny invertebrates. Ants are a favorite food for these frogs, but they will also eat other insects that are small enough to fit in their mouths. The Bolivian bleating frog is one of many species that are especially fond of ants. Other narrow-mouthed frogs have slightly larger mouths and are able to eat larger invertebrates. The New Guinea bush frog has a large head and especially wide mouth, which allows it to eat insects, as well as larger animals, like other frogs and lizards.

Scientists have not seen most of the frogs feeding, so they have to guess about how they go about eating. Some of the frogs probably eat insects that they find while they move about in trees or along the ground, but scientists think that many of these frogs may hunt by ambush. In this type of hunting, the frog sits very still. An insect that does not notice the frog may approach closely enough for the frog to grasp it and eat it.

Not all narrow-mouthed frog species have a tadpole stage, but in those that do, the tadpoles suck in water, sift out tiny microorganisms, and eat them. Microorganisms (MY-crow-OR-gan-izms) are living things that are too small to see. Scientists call this type of eating filter feeding, because the tadpoles sift, or filter, their food from the water. Some of the tadpoles have funnel-shaped mouths that are perfectly designed for filtering food from the surface of the water.


Most of the narrow-mouthed frogs are active at night, but they sometimes come out during the day. Those that live high in mountains are more likely to be active in the day time. Many of the narrow-mouthed frogs are burrowers and use flat scoops, or spades, on the heels of their feet to help them dig backward into the soil. The Bushveld rain frog, for example, has spades on each of its hind feet to help it dig. This frog can burrow as far as 20 inches (50 centimeters) below the surface. Others that burrow do not have the spades and instead use their front feet to dig into the soil head first. A few, like Boulenger's callulops frog, make their homes in burrows that they probably take from other animals, rather than build themselves. Many of the burrowing frogs stay underground during dry periods, only coming out during heavy rains. This behavior allows desert-living frogs to survive, but even the burrowing species that live in rainforests will crawl underground when the weather is dry.

Like many other frogs, most narrow-mouthed frogs defend themselves from predators by quickly jumping off, perhaps into a shrub where they can hide or into a nearby pond where they can dive out of sight. Some will also disappear into a burrow or try to dig down into the soil. A few narrow-mouthed frogs have more unusual defense tactics. One of the most bizarre is the tomato frog, a plump frog that lives on the northeast coast of Madagascar, a large island that lies east of southern Africa. The males are orange and grow to about 2.5 inches (6.5 centimeters), but the females are red and can reach 4 inches (10.1 centimeters) long and weigh half a pound (227 grams). Like many other frogs, the tomato frogs have skin that oozes, or secretes, a poisonous substance that tastes bad to predators. The substance in the tomato frog's skin goes a step farther. When a snake or other predator bites a frog, not only does the predator get a mouthful of white, bad-tasting goop, but the goop is exceptionally sticky—so sticky, in fact, that it can seal shut the mouth and eyelids of the retreating predator for several hours, sometimes days. Studies have shown that the substance is five times stronger than rubber cement.

Another narrow-mouthed frog with an unusual way of protecting itself is a broad-headed frog of New Guinea, near Australia. When it feels threatened, it holds its ground rather than running away, blows up its body, and opens its mouth to show off its bright, blue tongue. If the predator is not already frightened off by this display, the frog clamps its jaws on the predator and hangs on for several minutes. When the frog finally lets go, the predator often has had enough and leaves the frog alone.

Most of the frogs in this family mate when the weather is warm and rainy. In tropical rainforests, where it is almost always wet and warm, some species may be able to mate any time of the year. Those that live in very dry areas, however, mate only during the very short rainy season. The Bushveld rain frog spends most of its life underneath the dry ground of the desert-like areas where it lives. When the rains come, it comes out, usually at night, to search on land for termites and eat until it is fat. This fat helps the frog survive underground until the next rainy season. It also mates during this rainy period.

Depending on the species, narrow-mouthed frogs may mate in or near the water or on land. In both cases, the males begin calling when they are ready to mate. Some call with single or groups of ringing notes, while some have harsher voices. Many males have a bag of skin, called a vocal sac, on the throats. The vocal sac fills with air and deflates when the male calls. Other species have no vocal sacs, but still manage to call. In 2002, scientists reported that one narrow-mouthed frog, called the Borneo tree-hole frog, actually practices and adjusts its call, making it higher or lower to get the best echo from the tree cavity where it does its singing. The scientists said this was the first time any animal had ever been shown to change its call or song based on the place from which it calls. For other narrow-mouthed frogs, the males simply call. The females hear the calls and follow them to find the males. In the species that mate on land, a male's call may not only attract a female, but may also tell other males to find somewhere else to mate. The male horned land frog is such a frog. Males will often call back and forth, apparently to set up and keep their territories.

Species that mate on land usually do so in various hidden-away spots. These may include burrows that the males dig themselves, piles of leaves on the ground, tree holes, or plants that grow on the sides of the trees. The male Fry's whistling frog, for example, moves to the top of the pile of leaves where it lives and calls from there. Boulenger's callulops frog, on the other hand, calls from inside or near the entrance to its burrow, which it does not make but instead takes over from another burrowing animal. More than half of the narrow-mouthed frogs mate in or near water. The water may be a stream or other body of water that remains filled with water all year, or it may be a pool of water that dries up once the rainy season ends. Some frogs use very small pools of water that they find inside tree holes or within plant leaves that grow together to form small cups. Boulenger's climbing frog is an example of a frog that makes use of puddles inside tree holes.

Little information is available about reproduction in most of the 362 species in this family. Scientists assume, however, that the males and females of most if not all narrow-mouthed frogs mate like many other frogs: the male climbs onto the female's back as she lays her eggs. This piggyback position is called amplexus (am-PLEK-sus). In some species, like Bushveld's rain frog, the females are much larger than the males of the same species, which would make it difficult for the male to hold on if he didn't have some help. The help comes in the form of a sticky substance that oozes from the skin. It glues the pair together while they mate. In other species, like Boulenger's climbing frog, the males have sharp spines on one toe of each front foot. They probably use the spine to hang onto the females during mating.

In the species that mate on land, the females lay their eggs in a moist spot. In the Bushveld rain frog, the stuck-together male and female pair dig backward into the soil until they find a moist spot and she lays her eggs there. The eggs of this frog and most other land-mating species of narrow-mouthed frogs develop right into froglets, rather than turning into tadpoles first. The froglets usually look like miniature versions of the adults. Scientists use the term direct development to describe the growth of eggs right into froglets instead of tadpoles and then froglets. The food for each developing egg comes from a large yolk. Because the yolk is so large, the females usually lay only a few eggs at a time. A female Fry's whistling frog lays seven to twelve eggs, while a female Timbo disc frog lays just four to six eggs at a time. The males typically stay behind to watch over the young, sometimes even carrying them around on their backs. The males nab and gulp down insects that would otherwise eat the eggs and may also huddle with the eggs to keep them moist.


A tarantula could easily kill a frog, so why does the Great Plains narrow-mouthed toad make its home inside the large spider's burrow? This frog, which lives in parts of the United States, has formed an unusual relationship with the spider. The tarantula does not bother the frog, which is quite safe from other predators in the spider's home. At the same time, the frog eats ants and other insects inside the burrow that might harm and possibly devour the tarantula's eggs.

In the species of narrow-mouthed frogs that mate in the water, the females of some species drop their eggs in a pond or stream, while others lay their eggs in a pool of water inside a tree hole or within water held in plant leaves. The saffron-bellied frog is a species that mates around small pools that fill with water after a heavy rain. The females lay their eggs in the pools. The eggs of water-mating species may clump together as they do in the Bolivian bleating frog; they may float on the surface as they do in the ornate narrow-mouthed frog, or they may sink or float in other patterns. Frogs that mate in the water often lay hundreds of eggs at a time. One of these frogs, the ornate narrow-mouthed frog, lays several hundred. The Bolivian bleating frog lays about two hundred at a time, but the female may lay several clutches in a single season. One female Bolivian bleating frog was found with more than two thousand eggs in her body.

Once most water-mating narrow-mouthed frogs lay their eggs, both adults leave the eggs to hatch on their own. The females that lay their eggs in larger bodies of water, like streams or ponds, lay small eggs. For instance, two hundred eggs of the Bolivian bleating frog can fit into a cluster just 4 inches (10 centimeters) in diameter. These eggs hatch into tadpoles, sometimes in as little as a day and a half, and the tadpoles search for food in the water. In some species, like the ornate narrow-mouthed frog, the tadpoles have see-through bodies that make them nearly invisible. This helps them avoid predators.

Those water-mating frogs that use small pools of water for mating have eggs with yolks that are larger than the pond or stream species. Even after the tadpoles hatch from the eggs, they continue to rely completely on the egg yolk for food. This is important, because their tiny pools would likely not have enough food in them to keep the tadpoles alive. In some species, like Boulenger's climbing frog, the male stays in the tree hole with the eggs until they develop into froglets.


Even when scientists have never actually seen a particular frog species' eggs develop, they can predict whether they will turn into tadpoles or whether they will skip the tadpole stage and change right into froglets. The clue is in the yolk. Some frogs, including many of the narrow-mouthed frogs, lay eggs with a lot of yolk. This yolk feeds the frog developing inside. If the yolk is large enough, it can contain enough food for the developing frog to hatch right into a froglet. If the egg has a small yolk, scientists assume that the egg hatches into a tadpole, which must then find food on its own.


Some native people in South America, New Guinea, and perhaps some other areas eat narrow-mouthed frogs, but they do not take enough of the frogs to threaten the survival of any species. A few species, such as the Malaysian painted frog, are fairly common in the pet trade. Most, however, are rarely seen by humans in the wild or in the pet trade.


The World Conservation Union (IUCN) considers six species are Critically Endangered, which means that they face an extremely high risk of extinction in the wild; twenty-five species are Endangered and face a very high risk of extinction in the wild; thirty-six are Vulnerable and face a high risk of extinction in the wild; seventeen are Near Threatened and at risk of becoming threatened with extinction in the future; and 155 are Data Deficient, which means that scientists do not have enough information to make a judgment about the threat of extinction.

The Critically Endangered species include the beautiful nursery frog, which is also known as the elegant frog, and five others known only by their scientific names. These are Albericus siegfriedi, Microhyla karunaratnei, Parhoplophryne usambarica, Scaphiophryne gottlebei, and Stumpffia helenae. Most of these live in very small areas that are changing as people clear the land for purposes such as farming. Often, the frogs cannot survive these changes. Some of the species are also in danger from pollution and from global warming. Scientists believe that global warming in the future will cause weather-related problems, such as especially long-lasting, dry spells, that will harm the frogs and may lead to extinction for some species.

Since many of the narrow-mouthed frogs live in rainforests, and people continue to cut down rainforests, many environmentalists are worried about the future of these frogs, many of which scientists know little about. If the frogs have no place left to live, they will likely die off.

The U.S. Fish and Wildlife Service does not list any United States species of narrow-mouthed frogs to be at risk.


Physical characteristics: The Wilhelm rainforest frog has a dark brown or purplish brown body with yellowish tan spots and blotches on its back and legs. The snout is short and slightly upturned at the end. Its long, thin legs have lengthy toes that are tipped with wide, triangular-shaped pads. This species grows to 2 inches long (5 centimeters) from snout to rump.

Geographic range: The Wilhelm rainforest frog lives in the mountains of Papua, New Guinea, between 6,000 to 9,000 feet (1,900 to 2,800 meters) above sea level.

Habitat: This species hides among rainforest trees and in holes along the ground in steep areas, especially on the edges of roads, and sometimes in grass near streams.

Diet: Scientists are not sure what specific kinds of food these frogs eat. If they are like many other members of the family, however, they eat some types of invertebrates.

Behavior and reproduction: Wilhelm rainforest frogs may be found in many areas in the rainforest. They often climb high into trees, where they hide away in tree holes or inside plants that grow on the sides of the trees. They may also spend time along the ground, frequently tucked into burrows on the sides of stream banks or other steep areas. The males call females from inside ground burrows or from hiding spots high in the trees. They mate in either place. Females lay strings of two dozen or so eggs in the burrow or high in the trees. Scientists have little information on their reproduction, but one report noted a string of 27, 0.2-inch (5-millimeter) eggs in a burrow, along with a frog—probably the male—staying with them. Instead of hatching into tadpoles, the eggs hatch right into froglets.

Wilhelm rainforest frogs and people: People rarely see this frog in the wild. It is not common in the pet trade.

Conservation status: The World Conservation Union (IUCN) does not consider Wilhelm rainforest frogs to be at risk. This frog lives in a fairly small area, but the area is in good shape and the frog is quite common. ∎


Physical characteristics: The eastern narrow-mouthed toad has the typical teardrop-shaped body common to many members of this family. Its back and legs are light brown, gray, or reddish brown with patterns of darker brown lines or spots. The sides have a more faded color than the back. The frog's snout comes to a point, and it has a fold of skin that crosses the head just behind its small eyes. Its feet are unwebbed, and each of the hind feet has a spade for digging. Males have a dark throat, but the females do not. The frogs can reach 1.5 inches (3.8 centimeters) long from snout to rump.

Geographic range: Eastern narrow-mouthed toads live in the southeastern quarter of the United States. They have also been introduced to two islands in the Bahamas and to Grand Cayman Island.

Habitat: Although members of this species can survive in many on-land habitats, they prefer areas along the coastline. They usually stay off mountains and out of dry places.

Diet: Eastern narrow-mouthed toads eat mainly small invertebrates, especially ants, termites, and beetles that are 0.25 inches (6 millimeters) long at most.

Behavior and reproduction: During the day, eastern narrow-mouthed toads usually stay beneath leaves, under stones, or in other hidden spots along the ground. When discovered, they typically try to hop quickly away. They come out at night, which is when they eat. By remaining active at night and hiding during the day, the toads can avoid many of their predators, including garter snakes, bullfrogs, and large wading birds called egrets. When they are attacked, however, the toads can ooze a bad-tasting substance from their skin. This substance may be poisonous to a predator. The substance provides protection from the predators as well as the biting ants that the toad eats.

During wet periods of the year, the males begin calling for females from ponds and small rain-filled pools of water or from hidden places on land along shore. In southern areas, such as Florida, the males call from April to October. In cooler areas, they begin calling later and stop earlier. The calls last about 4 seconds and sound like the "baa" of a lamb. When a female finds a male, he holds onto her back with his front arms and makes a gluey substance with his belly that helps him stick to her. The female then lays her approximately five hundred eggs in several batches. The eggs float on the top of the water, hatch into tadpoles, which then turn into froglets. In warmer areas, the tadpoles may change into froglets in as little as twenty days, but in colder places, they may need as long as sixty-seven days to make the change.

Eastern narrow-mouthed toads and people: For most of the year, people only see this species in the wild if they search for them by flipping over rocks, logs, and piles of leaves that lay on the ground. The toads' loud mating calls, however, may help people find them during the mating season.

Conservation status: Neither the World Conservation Union (IUCN) nor the U.S. Fish and Wildlife Service consider this species to be at risk. It is very common throughout the southeastern United States, including suburbs where people live. ∎


Physical characteristics: The Malaysian painted frog is also known as the painted or Asian bullfrog, chubby frog, rice frog, and bubble frog. It has the teardrop-shaped body common to many narrow-mouthed frogs. This frog has no neck bones and, therefore, no neck, which gives it a chubby look. Its back is mostly chocolate brown with a wide, light yellowish to cream-colored band on each side of the body. The band is outlined with a thin, dark brown line. The yellowish cream color also covers the top of its snout between its large eyes. The frog has rather short legs, which are mottled with brown, light gray, and cream colors, and barely webbed feet. Each of its back feet has a spade for digging. The toes on its feet end in small pads. Malaysian painted frogs are one of the largest species in this family and grow to 3 inches (7.5 centimeters) long from snout to rump.

Geographic range: The Malaysian painted frog lives in southeastern Asia, including China and Taiwan, and parts of Indonesia. Populations also live in Borneo and Sulawesi, but people probably brought the frogs to these areas.

Habitat: The Malaysian painted frog is different from most frogs, which tend to stay away from towns and other places where people have moved in and made changes to the environment. Instead, this species lives in and around towns and avoids quiet, people-free areas.

Diet: The Malaysian painted frog eats a variety of small insects, especially ants.

Behavior and reproduction: For much of the time, the frogs stay out of sight by digging backward into underground burrows, into piles of trash, and into other secretive spots they find along the ground. When the rains come, however, the frogs come out to mate in pools that have filled with water. The males float in the pools and blow up their bodies to make calls that sound like loud honks. Females arrive and mate with the males. The female's eggs quickly turn into tadpoles, which rapidly change into froglets. This speedy growth is important because the water in their pools usually dries up in a very short time after the rains end.

Malaysian painted frogs and people: This species is fairly common in the pet trade. Although it lives near homes and buildings, people rarely see this usually underground frog in the wild. Some people, however, do hunt it for food.

Conservation status: The World Conservation Union (IUCN) does not consider the Malaysian painted frog to be at risk. This frog lives in a large area, and the area is in good shape. Moreover, even though it is collected as food and is seen in the pet trade, the frog remains very common in the wild. ∎


Physical characteristics: Pyburn's pancake frog has a wide rather flat back and a pointy snout that makes it look somewhat like a dead leaf. The frog is brown to yellowish gray with scattered, tiny, blue to cream speckles and sometimes dark stripes or other markings. It also has two, thin, light yellow to cream stripes, each of which begins at the snout and runs down the side of the body to the hind leg. The stripe widens onto the back where it has a ragged edge. The pancake frog's legs are short. The females can reach 2.2 inches (5.6 centimeters) long from snout to rump, while the males are a bit smaller.

Geographic range: Pyburn's pancake frog lives in northern South America, from southeastern Colombia in the west to French Guiana in the east.

Habitat: For most of the year, this frog moves along sandy ground in the rainforest. When it breeds, however, it enters the water of a nearby stream, which is also where the eggs hatch and tadpoles grow.

Diet: Scientists are not sure exactly what this frog eats, but they think it probably eats ants, which is what other closely related frogs eat.

Behavior and reproduction: Scientists know little about this frog outside of its breeding behavior, but they think the frog remains tucked away underground most of the time. When it breeds, the males call females from hidden spots near a stream. These hiding places may be underneath piles of leaves or inside tangles of plant and tree roots that poke up from the ground. The females lay eggs, which can be
0.2 inches (5 millimeters) across, in the quiet ponds of water or nearby. The eggs hatch into tadpoles that have sharp teeth, which they perhaps use to sift out sand as they suck water into their mouths. They then filter out tiny organisms from the water and eat them. The tadpoles scoot among leaves in the small stream where they were born until they develop into froglets and hop onto land.

Pyburn's pancake frog and people: People very rarely see this frog in the wild.

Conservation status: The World Conservation Union (IUCN) does not consider Pyburn's pancake frog to be at risk. This frog lives in a fairly large area. Logging, farming, and other activities are under way in part of its area and may be hurting the frogs that live there, but people have still not bothered most of the frog's habitat. Currently, Pyburn's pancake frog remains a common species. ∎


Physical characteristics: The banded rubber frog is black and pear-shaped with a wide body that becomes increasingly narrow toward the head. Two wide, red to orange red stripes run down the sides of the body from the snout over the eye and to the front of the hips. A red to orange red splotch also colors the rump. The body is smooth and quite shiny. Its short, front and back legs have numerous red spots. Its toes, which have almost no webbing, end in small pads. The front toes are quite long. Its underside is decorated with small white spots. Banded rubber frogs grow to about 2.75 inches (6.8 centimeters) long from the tip of the snout to the end of the rump. The tadpoles have a rather fish-like look, because their eyes are on the sides of the head rather than on top, like many other tadpoles' eyes are.

Geographic range: The banded rubber frog lives along the far eastern side of central to southern Africa.

Habitat: Even though they do not have spades on their feet like many other digging frogs have, banded rubber frogs are burrowers. They spend much of their time in underground burrows that they dig themselves.

Diet: The adults eat small insects, especially ants and termites. Tadpoles suck in water and sift out tiny organisms, which they eat.

Behavior and reproduction: During the day, they dig backward into the soil or into termite hills. Sometimes, they simply climb into holes in trees. They are active at night, when they come out on land. Instead of hopping, they either walk or run. By remaining underground during the day, they avoid most predators. When necessary, however, they can also protect themselves by oozing a substance from their skin that predators find to be bad-tasting.

In rainy times of year, the males move into or alongside puddles and small pools of water and begin making their calls. The call is a high-pitched trill that lasts several seconds and then repeats. Like other frogs, the males and females mate when the male crawls up onto the female's back. The female can lay up to 1,500 eggs, which drop into the water and stick to underwater plants. The eggs hatch into tadpoles that float heads up in the water, while wiggling their whip-like tails below. In about a month, the tadpoles change into half-inch (1.3-centimeter) tadpoles.

Banded rubber frogs and people: People rarely see this burrowing frog, except in the pet trade, where it is fairly common. If a person handles the frog, it may ooze from its skin the same substance it uses to protect itself from predators. This substance may bother human skin.

Conservation status: The World Conservation Union (IUCN) does not consider the banded rubber frog to be at risk. This frog lives in a large area and has a large population, even though it is a fairly common pet species. ∎



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Narrow-Mouthed Frogs: Microhylidae

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