 What is the similarity between a butterfly, a dolphin, a jellyfish and a leech? Well, they're all animals, but they're so different, right? That means the animal kingdom is really, really vast. In fact, the total number of animal species is estimated to be about 8.7 million. That's a lot. So how do we even begin to make sense of such a vast kingdom of organisms? And how do we classify them? Fortunately, there are very simple criteria which helps us differentiate them into phyla. So the animal kingdom has several phyla, singular phylum and plural is phyla. So in this video, we will take an overview of all the phyla that are there under the animal kingdom and look at some very basic criteria that we use to differentiate between them. Now, if you're not very familiar with how animals are classified, you will come across the names of a lot of phyla which will be very new to you. We'll come across many unfamiliar names. Don't worry about remembering the names just yet. Just try to understand the basic criteria that are used to classify animals into these different phyla and you will get these names once you go through other videos on each of these different phyla. So one thing that is common between all animals and in fact all living organisms is that they're all made up of cells. You must have studied that cells make up tissues which gather together to form an organ and organs gather together to form an organ system and several organ systems together form an organism. So these are different levels of organization. But there are some animals, in fact the most basic of all animals only have cells. They don't have the tissue or the higher levels of organization. They are that simple. That is the most primitive type of animals and they are the sponges. So there are these animals, some of them are really beautiful like this one, that only have a cellular level of organization and they form the phylum perifera. Perifera because they have pores in their bodies. That's why they are called sponges because sponges are pores, right? So these are the most primitive phylum of animals. Look carefully at this animal. Do you see any symmetry in their bodies? In fact these animals are so primitive that there is no symmetry. So what do I mean by symmetry? Take the human body. So you can imagine a plane passing through the middle of the human body like this. So here I've drawn a line but if you imagine three-dimensionally it will be a plane that will divide the body into two equal halves. So that is symmetry. You can make a plane pass through the body of the organism which will divide it into two equal halves. Bilateral symmetry is a type of symmetry. So this is bilateral symmetry in which there is only one plane that can divide the body into two equal halves. There is another type of symmetry in which there are more than one planes that can divide the body into two equal halves. Like in this flower. It's a type of symmetry that is present in animals as well as flowers. So for example take a look at this flower. You can have this plane divided into exactly two equal halves. Then there is this plane that divides it into two equal halves. Similarly there are three more planes. So there are five planes that divide this flower into two equal halves. So this kind of symmetry where there are more than one planes which divide the flower or the organism into two equal halves is called radial symmetry. So the most primitive type of animals the sponges as you saw they do not have any symmetry but the next most primitive animals they have some type of symmetry. Like our jellyfish over here. So a jellyfish can be divided by many planes into two equal halves. So the jellyfish belong to a phylum called Nideria. The old name for it is Cylinderata but this is the current name Nideria. The sea is silent. And there is another phylum just above Nideria which is made up of these marine animals. They also have radial symmetry and this is called phylum Tinofora. Again sea is silent. They are also called comb jellies. Again don't worry too much about the names if you're seeing them for the first time. When you read in more details about these phyla you will become more familiar with the names. Now these animals not only have some symmetry they also have tissues. Remember the phylum periphera the sponges they did not have any tissues. All they had was cellular level of organization. But these animals are a little more sophisticated. Their cells are organized into tissues and they had two layers of tissues when they were embryos. So this is what they looked like. This is called diplo plastic. Diplo means two. So there are two tissue layers in the embryo. So I can see here three one two and three. So what is the third thing? We'll come to it in a bit. First let's take a look at the two tissue layers. The outer one is called the ectoderm. Derm means skin. Ecto means outer. So it's the outer layer of the tissues. And the inner layer is the endoderm. Endo means inner. Now what is this white thing? It's actually a space. Its position is innermost to all the tissue layers. And that usually happens to be the gut. The digestive tract of the animal. Now phyla, nidaria and tinofora are diplo plastic. But animals which are higher than them they are triploblastic like over here. So this is triploblastic. Means these animals had three tissue layers when they were embryos. So the blue one again it's the ectoderm. The red one is the endoderm. There is another tissue layer in the middle called the mesoderm. Meso means middle. So ectoderm, endoderm and mesoderm are the three layers in triploblastic animals. Now in many textbooks and in videos you will find there is a layer that is shown even in diploblastic animals. That is not a cellular layer okay. There's something called the mesoglia that you'll find in some books that's formed by secretions by cells. But it itself is not made of cells. So that's not a tissue layer. Now animals which are a little more advanced than nidaria and tinofora are all triploblastic. These animals are also bilaterally symmetrical. Triploblastic animals have a few varieties. The first variety looks like this. This is pretty much the same that you saw just now. There are three layers ectoderm, mesoderm, endoderm. Then inside there is the gut. So these animals, the animals which have this type of arrangement of triploblastic tissue layers are called acelomate. And while they are called so we will see in a bit. So the phylum that comes under acelomates, there is only one phylum like that and it's the platyhelminthes. So this is phylum, platyhelminthes. Platy means flat and helminth means worm. So they are also called flatworms. And this example right here is a tapeworm. So tapeworm belongs to flatworms or phylum, platyhelminthes and our acelomates. The next type of triploblastic animals have something else besides the ectoderm, endoderm and the mesoderm. So here we have the ectoderm, here is the mesoderm, the red one is the endoderm. Now what is this blue thing that is something extra in these animals? And this is a space. Now this space is not the same as the white one, not like the gut. It's a body cavity. It's a cavity that is present between the tissue layers. And that is important because it gives the body of the animal some firmness and some resistance to let's say, you know, blows so that it's not squished. And it also is a place to hold internal organs. And in these animals, the body cavity is called a false selum. Why is it called a false selum? We will again see in a bit. So this type of animals are called pseudo selomates because pseudo means false. They have a false body cavity. And the phylum that has the false selum is called phylum nematode or ascalmyntis, the older name. They're also called roundworms because they're kind of cylindrical. And you might have seen many worms in your daily lives. You can see them sometimes in vegetables or in soil and stuff. Many of them are also parasites like ascaris. So these are the nematodes or ascalmyntis. So now I hope you understand why we were calling the previous types of animals as acelomates. Acelomate because they did not have any selum. They did not have any body cavity. That's why they were acelomates and these animals are pseudo selomates. So you must be wondering if there are animals with true selum. Yes, there are. All the animals that are higher than these are true selomates. They have a true selum. So ectoderm, mesoderm, the red one is endoderm, and the blue thing is the true selum. So why do we call this the true selum? And how is it different from the false selum? So the true selum, it is present within the mesoderm. So the orange one here, it is the mesoderm. And you see the blue thing, the body cavity, the true selum that is within the orange layer. So that is true selum. Whereas in pseudo selomates, body cavity was present outside the mesoderm. So here you see there is the ectoderm, the mesoderm, then the body cavity and then the endoderm. The body cavity is outside the mesoderm. Hence it is called the false selum. Another difference is in the false selum, the false selum is fluid filled. It's filled with a watery substance. Whereas the true selum, it's actually a space. Like for example inside human bodies, there is a space which holds all these organs, the heart, the stomach and everything else. That is the true selum. So these animals are called selomates because they have the selum. So what false under selumates? Well all the rest of the animals. All the animals higher to the pseudo selumates are true selumates and there are quite a few of these phylum. So first there is this phylum which has leeches. This is a leech and then it also has earthworms and it's called analida, phylum analida. Then there is the phylum with all the insects and spiders and scorpions and lobsters and prawns, crabs. This phylum is called arthropoda. Then there is the phylum with snails and oysters and octopuses and squids. And this phylum is called mollusca. Next is the one with starfishes and are called echinodermata. There is this phylum with these worm-like creatures which are found under the sea and they are called hemichordata. And finally we have the most evolved phylum of all which has the dolphins, the monkeys, the birds, the fish, the crocodiles and us and it's called phylum cordata. So let's just quickly go through once again what we saw in this video. So we start with the most primitive animals again. They only have the cellular level of organization and are the phylum perifera which has sponges in it. Then there are the diploblastic animals, the ones which have only two tissue layers in their embryonic stage and include the jellyfishes, phylum niteria and these comb jellies or phylum tinophora. Next there are the acelomates, the ones which are triploblastic. They have three tissue layers in their embryonic stage but no ceilum, no body cavity. And they include the platyhelminthes phylum. The flatworms an example is the tapeworm. Then there are the pseudoselomates which have a false ceilum and include the phylum nematode or asculminthes and include the roundworms an example is ascharis. And finally the ceilomates which have a true ceilum and all the more advanced animals. Phylum analida which has earthworms and leeches. Phylum artropoda which has insects, scorpions, spiders, prawns, crabs and many other animals. Then there is phylum mollusca which has snails, oysters, squids etc. Then there's echinodermata which includes animals like starfish. There's hemicor data with worm-like animals present in marine waters. And then there's the most advanced of all phyla. Corr data which includes mammals, birds, reptiles, fish and us.