 Now we talk about the vertebrates, vertebrates, the animals which have a vertebral column. Actually vertebrates have three major characteristics that is they do have a notochod. Actually notochod is a harder structure which makes the vertebral column. They have a collodorsal nerve cord which runs in the vertebral column and they do have pharyngeal slits sometimes called gill slits at any stage of their life. We classify vertebrates into five major classes called fishes, amphibians, reptiles, birds and the mammals. We talk about them one by one their characteristics and their importance. First of all we talk about the fishes. Fishes are the aquatic animals. These are present in freshwater, these are present in marine waters, these are present sometimes in pounds, these are present in lakes, these are present in rivers, in streams, in oceans, seas, even in the frozen seas. These are present in almost all types of water bodies. Fishes are of two major kinds. They may be cartilaginous, they have a softer skeleton and they may be bony. They have a more hard bony skeleton. Fishes, they have some specific characteristics. We can call them adaptations. They have a five-chambered heart which is a single-circuit heart because heart actually pumps blood towards the gills and then towards the body and then blood comes back to heart. We call it a single-circuit heart. Then they have gills for respiration for their respiratory gas exchange. They because they are aquatic they have to live in the water. They have specific organs called gills. Gills are rich in capillaries and when the blood flows through these capillaries and through the gills which are flooded with water, the gas exchange occur. The fishes, they produce usually large number of eggs and they do not provide parental care to their young ones. Fish they have, though some fish do it but most of the fish they do not provide a particular parental care but for its compensation they produce a large number of eggs. They are categorized among the animals called actotherms that is who cannot maintain their body temperature when there is a change in the environmental temperature. If they maintain it, they maintain it with the help of some behavioral mean that is moving from the colder water to the warmer water or vice versa. These animals, the fishes, they also have appendages which are called fins. Fins are the structures which are extended from various body parts in different ways, in different types of fishes and these structures actually help them in swimming and directioning that is changing their direction or so and swimming in the water. Fish are cultured in pounds and in different parts of the different types of like lakes and other water bodies for the purpose of making protein based food because fish protein is categorized in one of the best protein source available on earth. So fishes are very useful for us because they can provide us with a good source of protein in the foods and as we know that many of the people they make their fish farms and in which they grow some specific types of fishes whose meat makes a more good protein and they can grow maybe they can grow fast and there are different types of techniques which are utilized to increase the production of the fishes. Second important thing is this that the fishing industry also actually produce different types of products that is we use the fish muscles actually as the protein source that is for as food but there are a lot many other parts of the fish which we know their scales and their other body parts their fats they are there and these things are used to make different types of products which we call byproducts of the fishing industry. So fishing industry is one of the most important benefit of the fishes to the human beings. There are different types of fishes present on earth called like you know Rahu is a very common fish which is edible which is usually we eat it. There are carps which also grow very well. There are also large fishes which are even carnivore and sometimes they even eat upon they can eat upon human beings the sharks. There are some specific types of fishes called rays some of the rays are called electric rays because they can produce an electric current and that electric current is enough to kill human beings. Some fishes are very very large some fishes are very very small. We also culture fishes for ornamental purposes. We know that we usually keep aquaria in our drying rooms or in different types of public places which actually adds the beauty of that place adds to the beauty of that place. So there are many beautiful species of fishes small fishes usually that we culture for ornamental purposes. There are some very human friendly fishes like dolphin very very common fish the human children of the human and even adults like to play with the dolphins and they are very human friendly. So fishes are a very diverse group which have different types of characteristics and different types of benefits to the human beings. Now we talk about amphibians. Amphibians they are called a transition between the aquatic and terrestrial life. Amphibians includes the frogs the tores, salamanders and different organisms. These are also categorized in the ectothermic animals that is they do not produce usually endogenous heat that is heat from inside of their body by the metabolic reactions. They also warm up themselves if needed with the help of external factors. The amphibians they have usually a four chambered heart which is not whose two chambers called ventricles are not properly separated. They are mixed so the blood which is oxygenated and the blood which is deoxygenated mixes up but they do have a double circuit heart that is the heart receives blood from the body and it sends blood towards the lungs. The amphibians they respire through lungs in their adult life most of the part of their life is in on terrestrial that is on land they have lungs for respiration but for many times they go to water for example for reproduction they have to go to the water. They adapted certain mechanisms they carry out cutaneous respiration that is their skin is actually richly supplied with blood vessels and a gas exchange could occur with these through these capillaries skin and with the water. So we say that the carry out a cutaneous respiration through skin. Amphibians they actually go to water to reproduce. They produce large number of eggs sometimes even thousands of eggs they lay eggs in the water and these eggs they are for after some time of development converted into larvae. Lavae are aquatic structures they we can say aquatic form of this organisms they always live in water they are voracious feeders they eat a lot and we know that a lot many of these larvae actually eat upon the mosquito larvae which are present nearby. These larvae have gills for respiration because they live in water they have gills external gills when they grow up and they we call by a process called metamorphosis when they grow up and they are becoming the adults they start losing their gills and they depend upon the lungs for their further respiration. Frogs are very important because actually the amphibians they are very important because they also makes a very important part of the food chain they eat upon lot many of insects we know that larvae for example we know that larvae of frogs they grow in different types of water bodies and we know that larvae of different insects particularly mosquitoes also grow in the same bodies in water bodies like pounds in the same season and the larvae of the frogs they eat upon the larvae of the mosquitoes so actually they reduces the number of mosquitoes to be produced by those larvae so they are helpful for human beings and other organisms if they are frog larvae they'll eat upon the mosquito larvae the number of mosquitoes will be reduced if there are less frog larvae they will of course will eat upon less mosquito larvae and mosquito population will increase so they are very important part of the food chains and the webs of different ecosystems now we talk about the next group called reptiles the reptiles these are also ectotherms previously called cold-blooded animals reptiles are a diverse group of organisms which are actually adapted to tolerate the harsh environments mostly the dry and humid environments reptiles are though very common in habitants of almost all the ecosystems but particularly the thrive that is they grow very well in the deserts which are dry humid environments we know the different types of lizards snakes chameleons turtles tortoises they grow well in various harsher environments particularly in the deserts they have a four-chambered heart and two chambers are totally divided and the other two chambers the ventricles they are though divided but there is a small septum there's a small part the lower part which remains and which is not actually separated by this the division of the septum of the ventricles so some part of their blood mixes up with each other that is deoxygenated and oxygenated they also have a double-circuit heart that is their heart actually receives blood from the body and send words towards the lungs to oxygenated and from the body they receives actually the blood which is deoxygenated so they have a double-circuit heart for respiration they use as lungs because they are more precisely land animals they use as lungs for their aspiration for the gas exchange they also produces large number of usually large number of young ones and not usually and normally they do not provide a parental care to those organisms to compensate those that is to continue their race they produces lot many young ones there are a lot many reptiles very important for us like for example these lizards chameleons turtles tortoises they are very important parts of the food chains and food webs of different ecosystems snakes we know that snakes could be very highly poisonous they can kill different types of animals and even they can kill the human beings but there are certain snakes which are not poisonous and they feed upon the insect pests the pests different types of pests present in our crops like rats they eat upon the rats and they are not poisonous they eat upon the insects and this is how they help in say saving our crops from the pests but we cannot easily identify that whether a snake is it is poisonous or not but we know that snake venom that snake venom is actually used to make different types of medicines and particularly the treatment for the snake venom itself so snake venom is also important for an important thing for us because we use it in different types of medicines and treatment for snake venom itself. Some frogs the amphibians are also poisonous some amphibians also have poisons and some African frogs are that much poisonous that their poison can kill human beings and the even a horse so the amphibians and reptiles they are very important part of the ecosystems and sometimes they are harmful or they are harmless for us but indirectly sometimes they are useful for us like snake venom is used for making medicines you can see different types of reptiles a turtle can see a lizard very poisonous snake and you can see an alligator.