 Now, we talk about invertebrates and the vertebrates. We also talk about their significance, how they are important for us. Invertebrates, we talk about them first. Invertebrates are the organisms, the animals who do not have a vertebral column. There are lot many groups of invertebrate animals. We talk about them one by one and we start from the simplest. The first group that is categorized into animals and multicellular organisms are called the porifera. Porifera, the organisms which have pores in their body. We commonly call them or also call them sponges. The sponges are included in the phylum, the larger group. The phylum is actually a larger group in classification. So sponges, they are classified into the phylum porifera. These are the organisms which have pores in their bodies, which have porous bodies. These organisms have, usually they are attached on a substrate, maybe a rock, maybe the surface of the bottom of a sea. And on the other side, they have mouth. Mouth is the only opening in these animals through which water may enter or water may go out. They do not have any specialized organs. They are just multicellular organisms, which consist of two layers of cells. The external layer called ectoderm, internal layer called endoderm. Though they do have some specialized cells. There are some special types of cells present in their endoderm and sometimes their ectoderm, which help them in taking their food from the environment, which is of course water. How they actually take their nutrition? Water enters into their body through pores or sometimes through mouth. And their specific cells extract the food material, the phytoplankton or the zooplankton from that water by their ciliary movements. That is movements like cilia, they are actually hair like projections. And they acquire that food from that water and then remove that water back. Sponges, they are important for human beings. We know that we do lot many of our washings with the help of sponges. Sponges are used in the washing processes, these are the pieces of sponges, sponge organisms. Sponges are also used widely in sound proofing the environments. Whenever there is need of sound proofing, sponges, their bodies are made like this, that they absorb the sounds. So these are usually used for sound proofing of the buildings and sound proofing of some other materials like the recording instruments. Then comes the next group called the cilintrata. Cilintrata, for example, jellyfishes. These are mainly marine organisms. That is they live inside the seas and the oceans. They have some simple organs. They do have a mouth, they have specialized organs called tentacles, which help them in their movement as you can see in a picture. There is a jellyfish which have its tentacles below. These help this jellyfish in collecting its food from the environment. And it also help it in the movement. These organisms have a specific property. They have stinging cells, stinging, so dunk marine cells. They can sting. Whenever they have, they go close to a prey. Then upon their tentacles, some specific cells are present, which are called stinging cells. These cells produce a poison and also they have a long filament, which is usually present inside the cell. Whenever a prey comes close to them, they release those cells, those filaments from their cells inside out. These filaments act like injections for the body of the prey and they inject the poison in the body of the prey. The result is that the prey is either killed or may be deactivated. That is paralyzed and then they can easily eat upon it. They do have a mouth and they do have tentacles. Cylindrates also have a specific property. They produce fluorescent light. They are usually present in the lower layers of ocean, where almost no light penetrates. There are very few, we can say, molecules of the light, the photons that they do come. In those parts, these organisms, the jellyfishes and the others, they do live and they produce a fluorescent light. Sometimes they are called lights of the sea, because if the scientists or some people go inside that water in that area and they look at these organisms, they shine, they flourish, they produce light. So this is about the Cylindrates. Now we talk about the next group, which is the worms. Worms are actually categorized into different phyla, but we'll talk about them generally as worms. There are different types of worms which are present in the animal kingdom. Mostly these worms are the parasites. That is, they live inside or outside the bodies of the other organisms. There are different types of worms. Sometimes, as you can see in a picture, they're flat. Their surface or their body is like a flat tape. We call them flat worms. Sometimes they are rounded and they are long with both tapering ends. That is, both ends are pointed. We call them round worms. Sometimes they have a rounded body, but not both ends are pointed. So there are different types of worms. You can see on a site and we commonly see this one called earthworm. Many times when there is a season of rain, we know there's raining. Many brownish colored worms we can see on the surface of like grasses and mud. These are called the earthworms. So there are different types of worms. Worms have many times, they have a regenerative power. This is a specific property. If their one part is cut down and lost, they can again make their body part, the same body part in the same way. We call this property regeneration. So many of the worms do have a regenerative power, but of course not all of them. The flat worms and round worms, these are very important parasites of human beings. These flat worms are present in the intestines of human beings, particularly in the children. And they can actually eat upon all the digested food from the intestine of the child. When child become very weak, just like that round worms, they also live inside the different parts of the digestive tract. And they also feed upon the digested food material present in the intestine. And the person become weak slowly, though we can treat them with different types of medicines. There are different types of medicines which releases these worms from the body of the child or adult human being. How do they survive in that specific environment of the digestive tract? Because it's sometimes acidic, it is sometimes alkaline, and how do they attach there to the surfaces? Otherwise they will be flushed with the food. These worms have some specific mouth parts. With the help of those mouth parts, they attach themselves to the walls of the intestine. And when they are attached to the walls of the intestine, they can survive there. Though these infections are treatable, these infections are acquired from mostly soils, sometimes from water, and sometimes from eating the infected animal meat, which is poorly cooked. So this is very important that if the meat is not properly cooked, then it may causes the transfer of infection from the animal's meat to the human being. There are some other worms called flukes, the flat worms, which are present inside the liver. And these could also be transmitted if the meat that is the liver is not properly cooked. We call it kaleji usually. Kaleji can be infected with flukes. And a common way to check it is that if you cut kaleji into pieces, and press the parts, the pieces with your hands, then if these worms are in it, they will come out. The preference is not to use kaleji like this. So this infection can be transmitted. Then the next group, which is not a parasite, this is worm, earthworm. But this is extremely important because earthworms, they live inside the mud, usually under the trees, the plants. The earthworms are very important because they feed upon the dead organic matter. And when they feed upon the dead organic matter, they convert it into usable form for the plants. So it increases the fertility of soil in which it is present because it makes, for example, nitrogen, phosphorus, and other materials available for the plants. So earthworm is a decomposer which eat upon the dead organic matters. And it is beneficial for the soil because it increases the fertility of the soil. It means that worms, they are harmful and they are beneficial. Now the next phylum, arthropods. Arthropods are very widely distributed. We commonly know insects. Kiremakode, Asharatul earth. The insects, they are one of the most widely distributed and diverse group on earth. Actually, insects have much more species than all other, almost all other organisms. And they are very widely distributed. The phylum arthropoda have four major groups which are important. The arachnida, which includes spiders and ticks and mites. Crustacea, which includes many of the zooplanktons. The insects, which are present almost everywhere. Whenever you look at a soil, you look at water, you look at air, you find some of the insects like mosquitoes, like butterflies, not many others. Then the millipedes and centipedes. Millipedes and centipedes are some specific groups which are long worms and they are segmented and they have lot many legs. Arthropoda, the phylum, have some general characteristics. They do have an exoskeleton. That is, the skeleton, the skeletal support of their, support system of these organisms is present outside rather than inside. We know we have an internal skeleton. We have our bones inside the muscles and the skin. They have their skeleton outside. So we call them the organisms which have an exoskeleton, outside skeleton. They are segmented. Their body consists of segments. That is, it is divided into small parts. If we look at a butterfly, its body, not its wings, then you can find segments. Their body is, Arthur Port's body is generally divided into three regions. First one is called the head region. Second is called the thorax. And the third one is called the abdomen. The head region includes, of course, the head and the neck part. Then the thorax, which is, we can call it, almost the chest part. And then comes the abdomen, the softer part which have its soft organs. Now we talk about its four groups. The arachnida, the spiders, ticks and mites. These are the organisms which have actually four pairs of legs. That is eight legs. Spiders have some very specific characteristics. Many spiders, they are very poisonous. They can kill a person. Many spiders, they are harmless. We can, they are, they cannot actually harm anyone. We can see a lot many spiders in our houses which are making their webs on different places. They do not usually harm us. Spiders, they produce some specific materials with which you can see that they can make very fine threads. These very fine threads or materials sometimes are used in making certain products. Then the ticks and mites. The ticks and mites, they are parasites. They are actually the ectoparasites, mostly of the cattle. So they are important for us because they can harm the cattle which are the livestock of human beings. We culture them for our own purpose, for getting meat, milk, or eggs. They live upon the body surface of the cattle and they feed upon their blood. So ticks and mites should be controlled in the livestock. The lices. Jume. Jume is in the hair. They are also one of the arthropods. And we know that they have specific characteristics that they stick to the hair. They release some material that attaches and stick them to the hairs of the head or maybe some other body part. And when the sticky material is removed, they are flushed away. Then the crustaceans. Crustaceans are very important because these are present in lakes and fresh waters, mostly in some marine waters. They make the very important part called zooplankton of the food chains or the food webs. They are actually the link between the producers and the larger animals, the consumers of water ecosystems. Then the insects. Insects are very widely distributed. There are some very, very useful insects. Like we know that honeybees, they produce honey for us and for use of our children for us, ourselves. Honey is a product of honeybee and there are different types of honeybees, a small one, a large one, which makes different types of honeys which have some, their own characteristics, which are good for health and which are also useful for certain medicines. There are very harmful insects like, those insects like dragonflies, which can damage our crops. There are other damaging athopods like termites, which can damage our buildings, damage our wood, wood-based structures. So insects and spiders, the crustaceans, athopods, sometimes they are very beautiful. They're very like the butterflies, which makes or which actually adds a lot to the beauty of the nature. Sometimes they are very harmful for us. Sometimes they are very useful for us. We know the silkworm, which produces silk for us. There is a lac insect, which produces a material called lac, which is used in bindings and different types of other materials. So athopoda is a very diverse group and it is very widely distributed group on the planet Earth. Then comes the mollusks, phylum mollusca. These are the organisms which have shells and a soft body. Their body is soft inside and they have a harder shell. It includes snails, lobsters, there are certain lobsters we know which makes pearls for us. There are different types of shells which we use to make ornaments. This is also a very important group which is mostly marine, that is it is present mostly in the oceans and provides actually, say different types of products for us like the ornamental products. And sometimes their soft bodies are also eaten soft bodies are also eaten by some people for some medicinal purposes. We also grow lobsters for making pearls for us. Then comes the last group of the invertebrate called the echinoderms or the spiny skinned animals. Echinoderms, spiny skinned animals. Echinomene spiny, dermis, dermis the skin. These are exclusively marine. These are the animals which are present only in the oceans and seas. They have specific extensions of their skin which looks like spine and these spines actually help them into capturing their prey or handling with the environment. These organisms for their movement have a very specific type of system called the water vascular system. The water vascular system is a very specific system of tubes. Towards their ventral side of the body they do have lot many tubes which have a fluid that is its composition is just like that of the sea water. And these extensions are called tube feet. They actually, when they attach to a specific surface they produce a vacuum and due to that vacuum they attach to that surface and then by a thrush the whole organism, the animal moves towards that substratum with which they are attached. Then they are redirected and they attach to the next part. This is how the animal move. Echinoderms are thought to be the link between invertebrates and the vertebrates because they have certain specific characteristics which match them with the invertebrates and they have some other characteristics which match them with the vertebrates. So sometimes we call them a link between the invertebrates and the vertebrate animals. Examples are the starfishes, very common, you can see very beautiful starfishes present in our museum, different types of musia if you observe them. Other ones are called like sea cucumbers, sea animals which are very beautiful. Some are called feather stars which looks like in their appearance like a feather of a bird. So they also add to the beauty of the oceans. If we go down the ocean and towards its bottom we can see lot many Echinoderms adding to the beauty of the ocean and makes the very important part of the food chains and food webs of the seas and the oceans. So invertebrates, they are very important for us. For human use, sponges are widely used in soundproofing, in washing, worms are important because they are parasites of domestic animals and the human beings themselves. Insects are pests of many crops. So they are harmful, we have to handle with them. There are many useful insects like honeybee, lag insect, silkworm. There are different types of other invertebrates like lobsters which make pearls for us, culture them for making pearls. They are components of the food webs. They are components of the particularly aquatic food webs. They are components of terrestrial food webs. As the part of the food webs in the chains, they actually maintains the stability of those ecosystems. So this was about the invertebrates. They are important for us from various respects.