Animalia-chordata-amphibia


 * Amphibians media type="custom" key="10991928" width="40" height="40" ** By Jake Secor

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__Characteristics__ The three existing orders of amphibians are Anura (frogs), Urodela (salamanders), and Apoda (caecilians). Members of the order Anura, meaning tail-less ones, are well-equipped for moving on land by hopping. They catch their prey with their sticky tongues. Members of the order Urodela, meaning tailed ones, can live in water or on land. Members of the order Apoda, meaning legless ones, have no legs, as the name would suggest, and are nearly blind. They live in tropical areas and usually burrow in moist forest soil, or live in fresh water. Caecilians generally appear similar to earthworms. These three groups have traditionally been classified together in the Lissamphibia. While adult amphibians usually live on land, their soft eggs must be laid in the water; this is why they were named "amphibian" ("double life"). Young amphibians, like the larval frog or tadpole, spend their early years in the water, breathing through gills in the side of their head almost as fish do. In many ways, they resemble fish more than they resemble amphibians: they have no legs, and swim by wriggling their tail.(SP) The anatomy of an amphibian is that it has an inner skeleton, a vertebrate backbone, webbed feet with no claws, and attached limbs at the shoulders and hips. Frogs and toads have shorter, weaker, front legs and stronger back legs for jumping and leaping. (AR)



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__Acquiring and Digesting Food__ Methods of feeding vary based on type of amphibian. A tadpole, the larval form of a frog, lacks a strong digestive system and is therefore an herbivore. However, once developed into a frog, an Anuran has a more developed digestive system so it can become a carnivore that generally eats insects. Salamanders and Caecilians, on the other hand, skip the tadpole stage and their larvae look similar to the adults. Both the larvae and adults are carnivorous.

The frog's teeth are borderline useless and are present only on the upper jaw. The frog's tongue, however, is very specialized. The tip is folded backward toward the throat, and can flick out to quickly grab any prey. The food passes from the mouth into the stomach through the esophagus, and then into the small intestine, where the majority of digestion occurs. (JP- 5)

__Sensing the Environment__ Frogs and salamanders are able to see the environment with eyes. Caecilians, however, are nearly blind and must rely on feel to navigate. Although all amphibians are usually quiet, frogs become very vocal during mating season. Frogs use vocal signals to defend breeding territory or to attract females. This communication is made possible for frogs by the growth of external eardrums during maturation. Amphibians also navigate using the sky and stars, and use chemical signals to communicate breeding sites to one another.

An amphibian has two eyes to see the surrounding environment, and on land uses its third extra-protective eyelid. Amphibians have brains and a nervous system to sense the environment. (AR) __Locomotion__ Of tetrapods (vertebrates with two pairs of limbs) amphibians were the first to spend a substantial portion of their time on land. In order to do this, they had to adapt to be able to move around out of water. Frogs, salamanders, and caecilians all transport themselves in different, unique ways. Frogs use strong hind legs to hop around on land. Salamanders walk on land by bending side-to-side. Most caecilians burrow in soil and move by squirming similarly to worms. Although the name amphibian suggests a dualistic lifestyle, many amphibians live their entire lives only on land or only in water.

__Respiration__ Most amphibians live in water, close to water, or in a moist environment because moisture is often a key part of gas exchange. Swamps and rain forests can be popular places to find amphibians because of abundant water availability. Even Anurans that are adapted for dry environments spend most of their time in moist areas. The moist skin of amphibians is often used to carry out gas exchange with the environment. Therefore, it is extremely important that amphibians' skin remains wet. Some land amphibians do not even have lungs at all and rely completely on gas exchange through their skin and oral cavity. Because amphibian eggs do not have shells, they dry out easily when they are not in moist areas.

The amphibians have a three chambered heart(MP-3). media type="youtube" key="Nfojq4ikHH0" height="315" width="420"RJ



__Metabolic Waste Removal__ The kidneys of amphibians, similarly to freshwater fish, excrete dilute urine when salts from the fresh water accumulate on the amphibian's skin. Because dehydration is such an important concern for amphibians that live on land, frogs conserve body fluid by reabsorbing water across the epithelium (a type of tissue) of the urinary bladder.5

Wastes excreted by amphibians often take the form of ammonia, due to how easily it can be diluted/eliminated in water. The excretion of ammonia also underscores amphibians' need to be in close proximity to water. (Matt B - Source 4)

__Circulation__ Amphibians have a three-chambered heart consisting of two atria and one ventricle. Their circulatory systems have a pulmocutaneous circuit and a systemic circuit that work together to bring blood to the systemic organs under high pressure. Some oxygen-rich and oxygen-poor blood mixes in the single ventricle.6 7 The ventricle is divided into narrow chambers, so that mixing is relatively low. Fairly pure oxygenated blood is sent to the brain, and fairly pure deoxygenated blood is sent to the lungs and skin. The only blood that has been thoroughly mixed is that that is sent to the body, and, even so, this mix has more than enough oxygenated blood to supply the body with oxygen. (PS Source 8) __Self Protection__ A concern for amphibians is being eaten by larger predators. Many species of amphibian have colored skin that camouflages them with their environment. Amphibians that secrete distasteful or poisonous mucus often have colored skin to send a message of danger to predators. By being a threatening color larger animals will associate the color with danger and avoid the amphibian. The poison of some frogs is so effective that indigenous people would put the poison on their arrows to make them more effective for hunting.

Most amphibians have developed epidermal glands. These glands are able to secrete protective mucus or toxins. The glands are alveoliform, are extensions of the epidermis, and end as a pore. The mucus that is secreted is used as a defense against microorganisms and reduces moisture loss. Certain toads, newts and salamanders have paratoid glans normally found behind the head and are what people often claim are "warts". The glands can burst when pressure is applied and in some case can excrete or shoot out releasing a toxin inside of the gland. (MS 11)

__Reproduction__ Most species of amphibian use external fertilization for reproduction. The male grasps the female to tell the female to release her eggs. Once the eggs are released into the water, the male spills his sperm over the eggs. The eggs have a jelly coat but no shell so they would dry out if they were released out of water. Some amphibians lay many eggs at once with high mortality rates while others lay few at a time and show some parental investment. Depending on the species, fertilized eggs might be kept on the back or in the mouth or stomach of the male or female. They may also remain in the female's reproductive tract.

The eggs amphibians lay are amniotic, meaning they don’t have shells but have instead gelatinous layers. From these eggs hatch aquatic larvae which respire by the use of gills. The larval stage varies greatly among different amphibians. (TB)

__Osmotic Balance__ Amphibians live either in water or in very wet environments. Dehydration is the most present threat for amphibians because they dry out easily. Therefore, the skin is designed for the exchange of water with the animal's environment. Amphibians also reabsorb water after using it so they can get the most out of the available resources. It is important for amphibians to live in stable environments that face no risk of drought because they must have constant access to a body of fresh water or wet soil. Amphibians in drier areas will even stay on leaves if they provide more water than does the ground.

For example. a frog's bladder in water quickly fills with a hypotonic urine (which transports the water in the environment into the body). On land, the water is then reabsorbed into the blood to compensate for the water lost during the evaporation through the skin. This absorption is controlled through a hormone (similar to ADH in mammals). This is an instance of an amphibian making efficient use of it's water content (RK)

__Temperature Balance__ All amphibians are ectothermic so their normal body temperatures are not effected much by their low metabolic rates. Normal temperature ranges vary dramatically among species of amphibians. Water is important for amphibians because they lose heat rapidly when exposed to air because of evaporation due to their moist body surfaces. When they are cold, amphibians move into the sun. When they are hot, amphibians move into the shade. Some bullfrogs can also secrete varied amounts of mucus depending on body heat to return their temperature to normal.

To protect itself from the harsh temperatures of the summer, the amphibian often hibernates called estivation. A similar phenomenon occurs in the winter to prevent freezing. (AR) Amphibians are cold-blooded animals. This means that instead of having a constant body temperature, they take on the temperature of the environment. While the moist, scaleless skin of frogs helps them to absorb water and oxygen, it also makes them more vulnerable to dehydration. If the skin of amphibians dries out, they die. As a result, amphibians are often found near moist, freshwater environments such as ponds, marshlands, etc. Some amphibians become inactive when conditions are unfavorable for survival. This period of inactivity is called estivation when it occurs during hot, dry weather and hibernation when it occurs in response to cold temperatures. Activity resumes when favorable conditions return. (VN)

When conditions are unfavorable for the survival of the amphibian, such as when the weather is too hot or the weather is too cold, some amphibians enter a period of inactivity to conserve energy and water, which is achieved by slowing down their heart rates, rate of breathing, and other metabolic processes. In unbearably cold weather, the process of entering a period of inactivity is called hibernation; when the weather is too hot or dry, this process is referred, rather, to as estivation, Once favorable conditions return, the amphibians become active again. (MR, Source 12)

Ever Wondered the Difference Between Frogs and Toads? (AP) Frogs tend to have wet skin as well as long hind legs that help them jump. Some types of frogs are also able to jump. Toads on the other hand have dry skin with warts. They are fatter, rounder, and shorter than frogs which forces them to stay close to the grounds. A common misconception is that only frogs are poisonous and not toads, but in fact, a few types of toads are. Toads have a special gland behind their eyes called parotid gland filled with poison. They can use it as a defense mechanism by squirting it at the attacker.

__Review Questions__ How are amphibians able to live on both land and water? (CP) Describe how important water is for amphibians. Be sure to include the effects water has on temperature balance, osmotic balance, reproduction, waste removal, and respiration. (IL) Describe the circulatory system of amphibians. How might the amphibian circulatory system be less productive than that of mammals? (ZJ)

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http://www.baileybio.com/plogger/images/ap_biology/animal_diversity_project_-_must_cite_your_textbook_/amphibian_-_cutaneous_respiration.jpg (MB)

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[] (MM)

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7. Duellman, William Edward, and Linda Trueb. "Chapter 8: Relationships With the Enviornment." //<span style="background-color: #ffffff; font-family: 'Times New Roman',Times,serif; font-size: 16px;">Biology of Amphibians //. New York: McGraw Hill, 1986. 217+. Print. (VN)

http://www.youtube.com/watch?v=Nfojq4ikHH0

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9. <span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 11pt; text-decoration: none; vertical-align: baseline;">"What's the Difference Between Frogs and Toads?: Amphibians: Animal Planet." Pet Guides and Wild Animal Guides:Animal Planet. Web. 29 Oct. 2011. <http://animals.howstuffworks.com/amphibians/toad-info2.htm>. (AP)

<span style="background-color: transparent; color: #000000; font-family: Arial; font-size: 11pt; text-decoration: none; vertical-align: baseline;">10. "Vertebrate Kidneys" [] (RK) 11. "Amphibian Articles - Toxicity and Defense Methods of Amphibians." //Livingunderworld.org | Amphibian Information Resource//. Web. 13 Nov. 2011. <http://www.amphibiainfo.com/amphibianArticles/article0011.shtml>. (MS)

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