hi everybody and welcome back today we're going to be looking into animal diversity in this video i'm going to cover the different ways in which we allocate subdivisions of animals so how we look at their symmetry their body tissue layers and their celiums and then we're going to look at the specifics of the major animal groups now a really important skill that you are going to need for animal diversity is to be able to read off a phylogenetic tree which is what we have in the camera in front of you now and what i'm going to do is i'm just going to zoom in on a particular part of this so that we can see a little bit closer and basically what a phylogenetic tree is is a timeline of how organisms have appeared and along the way there are different physical characteristics that appear and so if we look at the very very base of this animal diversity tree we will see that everybody contains a multi-cellular common ancestor now that multi-common ancestor probably is something like a protest and from there outwards we have all of the animal groups that we see today now what's important to understand about phylogenetic trees is that they show us common ancestors and common ancestors are often located at these points of divergence so there would be a common ancestor here there would be another one over here and so on and so forth if we look a little bit higher there would be a common ancestor over here but there would also be one over here and so essentially what you're doing is you are looking for how many common ancestors do animals have in common the more common ancestors they share the closer they are in relation to one another now this particular phylogenetic tree is quite useful because what they have done is along each of the divides they've told you what the animal has so if we go back to the beginning and we look at this first common ancestor they are saying that this particular individual split into two possible groups one that had no tissues and one that did have tissues the one that went with no tissues continued on this pathway which if we look a little bit higher you'll actually see it becomes sponges and if we go the tissue root there was then another point of change this common ancestor resulted in either having radial symmetry or bilateral symmetry and so on and so forth but how do you actually calculate how related an individual is well you need to look at how many common ancestors that they have in common with one another so if we were to zoom out a little bit and move to the higher part of this phylogenetic tree we are going to see how many common ancestors these individuals have so let's say for example the question wants to know who is more closely related and let's say the question is who is more closely related mollusks or you know snails and that kind of thing and annelids or mollusks and arthropoda so who's more closely related to one another so here's the thing we need to see how many common ancestors they share now what you could do is you could go all the way back to the beginning of the tree and you can count how many common ancestors we share so we have one two three four let's move this up four we have number five over here and then we get to number six now up until number six everybody shares these six common ancestors out of the three uh of the mollusks the annelids and the arthropods what's important here is if you notice at point six we branch off into the mollusk branch and then we also branch off to the right here and there's another common ancestor so this would be technically common ancestor number seven so now that means that who has the most common ancestors shared with one another while mollusks have six in common with analysts and arthropods but annelids and arthropods have seven in common with one another they have this extra one that happened after mollusks appeared or at least started their evolution and therefore annelids and arthropoda are more closely related to each other because they share more common ancestors and so that's what you're going to need to do is count how many ancestors they share and the more ancestors they share the more likely they are closer in relation to one another so when classifying an organism we need to first of all look at its symmetry because this is going to allow us to put it into one of three categories now the first category that we can find in terms of symmetry is going to be something like asymmetry or in this particular picture they just say it has no symmetry none asymmetrical organisms there is only one asymmetrical organism and that is peripheral or sponges the second option is radially symmetrical which means that no matter which way you cut the individual as long as you cut it through the center you will always have the same half on either side and this is very clearly seen in examples like nadaria or jellyfish and see an enemies the final kind that we are used to seeing is bilateral symmetry and this is where the majority of animals on earth lie and that is simply because if you cut them down the center of their bodies from the anterior end to the posterior end they will make two identical copies or there will be two mirrored sides to each of the organism now this symmetry reveals certain things about the organisms there are certain advantages for different kinds of symmetry so let's look at asymmetrical structures like sponges they have a blind ending gut which means that technically any food that goes in to their body cavity actually enters through exactly the same opening so they don't actually have a complete digestive system they have no true tissues they're the only one that we know of in the animal kingdom that possesses no true tissues in actual fact they're only made out of two cell layers they don't actually have specific tissues they have no sealant which means they have no body cavity on the inside for organs to grow in and and be independent we'll go into more detail later what a selim is and lastly they are scissile which means that they do not move around and so some of these advantages is that they can grow almost anywhere in water in particular they're simple filter feeding organisms and they lack the majority of a nervous system so they can't sense anything around them now in terms of radially symmetrical organisms we are going to see organisms that can sense in a multitude of directions they don't necessarily have a very specialized sensory organs yet that comes much later but however they are able to search for food in all directions now they are made out of tissue layers and they have two tissue layers we're going to get to what those are soon they often comprise of a hydrostatic skeleton which means that their skeleton is made out of water and that their skeleton is kept under pressure and most organisms that are rarely symmetrical actually have to live in water because their body needs to be supported by the water around them they have no selena either which means they have no body cavity and if you don't have a body cavity you are not going to have specialized organs and last but not least they have a single or also what we call a blind ending gut as well it means the opening that goes into their body is the same opening that waste would leave their body finally bilateral symmetry now the advantages of that is that you have something called cephalization cephalization essentially means that at the anterior end which is basically where the head is of an organism you will find a cluster of sensory cells in other words you will find a brain and you will have sensory organs and it's not just limited to eyes and ears there are many other sensory organs that other animals possess that perhaps humans don't another thing about bilateral symmetry is that anyone who is bilateral will have three tissue layers and because they have three tissue layers they will have some form of celium in other words they'll have a body cavity in which they can have very specialized organs that allow them to do specialized functions now once we've classified our organism by their symmetry we're going to look at their tissue layers and besides sponges sponges are the only ones who don't have either diplo or triploblasts they're just cell layers so they don't actually have any tissues um they fall into one of these two other categories now as far as we are going to know the only organism that is a diploblast is nadarians which we'll get to soon diploblast means di means two and so that means that there are only two uh tissue layers and the two tissue layers that we see in diploblasts are going to be the endoderm which is this very central layer that is what is going to grow into the digestive system so think the stomach the intestines and then the outermost layer is going to be the ectoderm and this would grow into the skin but if you're a slightly more complex organism you actually have a few more of these structures and that's why you're called a triploblast triplo meaning try you are made out of three tissue layers starting yet again you do have an endoderm because you need an endoderm to form your digestive system right in the center and then you have a middle layer which we call the mesoderm now the mesoderm is a really important layer because that's the layer that you grow all your other organs out of so that means that lungs heart liver kidneys they grow in this particular layer and if you don't have this layer you can't grow those organs which means you're not that very complex as an organism and then last but not least the triploblast also has an ectoderm and that ectoderm like i said grows into the skin and possibly the nervous system of that organism now the one thing i didn't mention for now is this non-living layer that you may be able to find in diploblasts and this non-living layer is sometimes what we see in organisms with hydrostatic skeletons like nadarian so like jellyfish and basically it's a place for them to store water to give their body shape now let's look into celiums so at this point we've classified organisms by their symmetry and if they have bilateral symmetry they will be a triploblast if they are a triploblast which means they have three tissue layers they will then have a form of a selene now as we look into a more detail of the sealant we can see that you need to know the tissue layers before you understand this next topic and so each of these organisms has an ectoderm on the outside and it has an endoderm on the inside representing its digestive system the other layer the mesoderm as you see in the pink here is slightly differently arranged depending on which of the columns that you have and so as we move from left to right i'd like you to take note of how complexities increase in other words if you are starting at the beginning you have a very very simple body plan but as you slowly move towards celamates and then finally sorry pseudocolomates and then celamates you'll see that the organism was become bigger and more complex so let's start off with celamates an example of a selamat would be like a flatworm and these flatworms which we'll speak about later they're very very simple organisms and you'll notice that their tissue layers are somewhat solid there's no empty spaces in between them until we get to the digestive cavity in the middle that's the only hollow space and so what that means is is that any organs they do grow are within these actual tissues and so they will sit in this space and what that means is that the organ itself actually runs through the entire organism it's not necessarily separate from other organs if we look at pseudocoelomates an example of these could be round worms some round worms we're familiar with would be like parasitic ones that perhaps lift live inside your digestive system they're a little bit more complex because now what you find is they have a pseudo selamate and so what that means is they have this empty space over here which is a cavity it's basically an empty space that you can put organs inside of it but these organs are not very complex because unfortunately they can move around a lot on the inside they're not very stable and they might be repeated throughout the organism as well but we are getting a little bit more specialized the organs are definitely getting a better higher more complex function but the final picture in this story is going to be celamates and this is where the majority of organisms or animals actually lie and you'll notice that they also have yet again an ectoderm and a endoderm with the mesoderm but you'll notice that the mesoderm actually sits almost like an outer ring and then an inner ring so if this over here is the outer ring and here is the inner ring what it does is it provides this c-shaped or this semi-circular space on either side and why is that important what function would that hold well it's important for it to be there because that is where we are actually going to grow our organs and not just grow them we're going to keep them separate from each other they are going to be independent and they're going to function independently of one another and why is that so important because if organs are separate from each other they can grow bigger they can be more complex and specialized which means that they can do functions that are a lot harder for organisms that don't have this now if it's difficult to imagine what this is like you need to imagine the inside of your body being like a lunch box and inside of a lunchbox you have sections that have been divided by plastic on the inside and then i want you to imagine your organs being like pieces of your lunch like a sandwich or a piece of fruit and they're going to be separated from one another with cling film so you're going to individually wrap the organs you're going to place them in the cavities of the lunch box and then you're going to put the lid on top and that's basically how the inside of the body is structured where you have these individual cavities with individual organs so what is the advantage of having a sealant well the first of all thing is that you need to know that our organs are going to slowly get bigger and that makes sense because as the organs get bigger the organism actually gets bigger as well because it means that there are more complex reactions that can take place which then leads me to the fact that our organs grow independently of one another and what that means is um the heart can grow separately from the lungs they're not like attached to one another it's not like as the heart gets bigger the lungs get bigger they can do their own thing they can repair themselves separately of one another and another thing is that we can also have more complex digestion which means that there's a bigger range of foods that can be eaten which is a great advantage because what it means is that if one food is missing you can go out and find something else that's similar and still get the same nutritional value and if you can eat more foods it also means that you can actually live in more places it means that you are adapted to suit more than one environment which makes you a lot more successful the first of the animal phyla we're going to look into is peripheria and peripheria are also known as sponges and sponges come in a variety of places and particularly in aquatic environments uh fresh water and salt water and they are our simplest and oldest animal and they have been very unchanged for a very long time it's important to know that they do not move so they are sessile which means that they are stuck to whatever they are growing on in this photograph here we can see they're growing on a rock alongside also with some coral sitting in the center here and we'll get to coral soon what's really important about periphery is that they ought to sell layers thick they are not to tissues layer thick and that's a really important one that's one that a lot of people get wrong um intestine exams and they confuse um cell layers with tissue layers remember cells and tissues are not the same thing and finally we know that peripheral are filter feeders and essentially what that means is they pull water in through these little pores so these holes on the side so they suck water in they filter feed and they have these cells on the inside that trap the food and then any excess water with any food particles they don't want or any wastes will come out of the top of these holes so that's the opening at the top where we have any waste products and this is also why they don't actually have what we'd call a gut because they simply just feed through the openings on the sides of their body so we wouldn't even call it a blind ending gut although some textbooks do refer to them as that because they only have one way in and the same way out um just depends on the textbook that you have the next phyla we're going to look at is nadaria now nadaria come in a multitude of varieties the some that we are familiar with are jellyfish corals like you can see in the photograph alongside and see an enemies and what a lot of people don't realize when they look at coral like in the photograph alongside is that this entire structure is a collection of nadarians living together and so we can't see in this picture but if you were to zoom up a little bit closer on each of these little spikes you can see there's these tiny little bumps and each one of those little bumps is an individual nadarian polyp and i'm going to go through the different body structures that they come in very soon but that links to my next point in that they are aquatic and they live with two different body forms and now these two body forms that they have have either been a medusa or a polyp i'm going to go through what those are in the next slide they are diploblastic so they've got two tissue layers they have two true tissue layers they have a hydrostatic skeleton some of them do whereas for example our coral alongside here actually just uses a a calcium compound in order to grow themselves on top of it that's what makes coral hard that's often why people think that coral is actually not alive but it is and the most defining thing that nadaria have is they have something called a nemotocyte which are stinging cells and we're very familiar with these in jellyfish and these are the cells that sting you if a jellyfish tentacles touch you but coral and an enemy also have these stinging cells essentially the cell is sort of a rectangular shape and sitting inside of it is a spring-like tail with a barbed very sharp sort of pointy end to it and basically this very sharp structure will shoot out of the cell so if this is what the cell looks like and this is what it looks like when it shoots out basically what happens is because it's bobbed it means that these little ends so i'm talking about these little ends over here because they're points they point inwards like that what happens is is that when they go into your skin they can't be pulled out because in the barbs flare outwards and it's very painful and so that's also why you also experience some pain when you're stung by jellyfish is that those bobs get stuck in your skin and often many of them have some kind of toxin in them that's what the dorians use to catch fish and what they feed off of and they basically sting their prey in order to kill them now as i said before nadarians come in two body forms and so the two body forms that they come with are either going to be the polyp form which is what we see most coral and in enemies and if you see a jellyfish it's in the medusa phase but what you'll notice is that these arrows indicate that they can actually swap between the two phases and that's actually very true the weird thing about nadarians is that we don't really know how long some of them last for because what they're actually doing is when they go in between these two body forms they're going from a juvenile which is dev just generally what the polyp is it's a juvenile nadarian and they become a medusa and they can swim around and move around and so for example a baby jellyfish will be a polyp it will then grow into a medusa but here's the weird part that adult jellyfish can reverse itself a group of itself and go back into being a polyp and it can essentially live forever and in some instances we don't know how long jellyfish actually live for because they can do this now that doesn't mean that all nadarians can do this and that is also why when you look at um coral coral is permanently in the polyp stage it's not moving around and you just have to imagine it being like an upside down jellyfish it's got all of its tentacles floating out towards the outside of the body because that's where the fish are going to be swimming it's got its mouth in the center and you'll also notice that it's got its gastrointestinal cavity sitting in the middle here and so what that means is food can come in here but it also means that food is going to exit out the same place which means that it's a blind ending gut it means its mouth and its anus are technically the same place now because it is a triple a diplo blast excuse me it's got two tissue layers it's got an ectoderm and an endoderm it doesn't actually have a mesoderm what it does have however is something called a mesogly and if you remember way back at the first slide i spoke about this like non-living like layer that some organisms have that are diploblastic this is the non-living layer the mesogli is a jellish layer that's filled with a gel and it keeps the body shape of our nadarians in place and gives them structure the next phylum is platyhelminthes now this is the most unusual phylum only because it has a mixture of strange characteristics that doesn't make it as complex as its round worm and annelid cousins other worms but it doesn't also make it as simple as perhaps a jellyfish nadorians and so they have some characteristics but they lack others now an example of uh platyhelminthes are most commonly flatworms and flatworms are free living worms that live mostly in aquatic environments so saltwater and freshwater and what's unusual about them is they have some complex aspects to them but also some not so complex things which is what puts them sort of in the middle of all the filer and they do have a single gut which means that the structure they feed with is also the structure that they will remove solid wastes with so it's the same opening they are free living which means that they can live out in the wild and they don't need to like live with other organisms um these examples along in the picture here are sea flat worms so you would find these in the ocean but some of them are actually parasites which means that they may actually live inside of you and an example of this would be a tapeworm now this is the unusual part so platyhelminthes have a single gut which means they don't have a very complex body structure but they have cephalization which means that they have a anterior end if you remember it's the it's the where the head would be and that means they actually have a cluster of specialist sensing cells they have a very very basic nervous system with a very very simple brain we don't want to really call it brain at this point because that's not what it is in terms of their tissue layers they do have three tissue layers and that then means that they have some form of uh or may have some kind of selamat but because they don't have um any space in between their layers their tissue layers we call them acelamates as we've mentioned before in our previous slide now a step up from our platyhelminthes is analeta and analida are our segmented worms um examples of these can be earthworms that we're familiar with and also leeches but there are many others and now we've got slightly more complex we're now getting closer to organisms we're more familiar with now analeta are well known for having hydrostatic skeletons because of their hydrostatic skeletons they also need to be very careful with their water and they need moisture to live often you will find that a lot of these analeta live in wet aquatic environments but some of them for example like earthworms they live in soil but the soil actually needs to be damp and the reason for that also is because a lot of analytica they breathe through their skin they don't actually have lungs and so moisture is really important for gaseous exchange now they are triploblastic which means they have three tissue layers and because of that it also means that they do have a sealant remember that means they have a cavity where they can have lots of specialized well-developed organs and the last component is that they do have cephalization think of it like this the more complex your organs are the more likely it is that you will have a brain and you will have specialized sensory organs the less likely your organs are specialized the less likely it is that you will have a brain and so civilization essentially means that there is an end a head and a tail to the organism and the head has the majority of the sensory organs in it which in adelaide's they do and it's fairly well developed the second last phyla we're going to look at is arthropoda and arthropoda are yet again one step closer to being a more complex organism they are actually very complex because they share a lot of characteristics that our own animal group have and examples of arthropoda are insects spiders and crabs and what makes them so defining is their exoskeleton and remember that's this hard structure on the outside that provides them with protection it also means that they have to shed their exoskeleton once a year it means they have to molt i mean that's because their skeleton doesn't grow with them in other words they outgrow their exoskeleton every year and they have to grow a new one now um arthropods are the most successful organisms on earth they live in every environment they have managed to live everywhere from the ocean to soil to rainforest sky it doesn't matter they literally live anywhere and they are so successful because they can avoid dehydration and remember even in extreme cold and extreme heat there is still a lack of water or liquid water available and arthropods are really good at living in places without any water now they are triploblastic so they have three tissue layers which means they have a celium and that comes along with having cephalization and we can we can imagine cephalization a bit better in other pods because we can actually see their head with their eyes and their antenna and that makes them the second most complex group that we're going to look at last but not least we have chordata and this is the group that we fall into it's the most complex organism it's also the phylum that has the largest organisms as well and that's because as you grow bigger you need more complex organs and so they go hand in hand with one another and so who falls into this category well some examples are bird fish and mammals and the defining characteristic of chordates is that they have an endoskeleton which means their skeleton is on the inside and it's made out of either bone or cartilage the second thing that's really defining is that we have a spinal cord and that spinal cord runs along the dorsal side of our body in other words along our back um and you can see this in birds fish reptiles the vertebral column with the spinal cord on the inside runs along the back part of us now this means that we actually have advanced cephalization it means that we have the most well-developed sensory organs the most well-developed brains as well most of us have around four appendages and so that means we're actually sort of segmented as well just like we have segments in worms and we have segments in insects humans and other animals are also segmented and we've got sections to our body so our abdomen our thorax our arms and legs are technically segments of one another so we have at least four appendages and we are also triploblastic so we've got three tissue layers and because we have threo tissue layers we have a true and that then means that our organs can be very well developed and that we can be very very well specialized now normally at this point of the video i would be doing a terminology recap but there is an enormous amount of terminology in this subject in the specific topic so what i suggest is going back having a look at the specific screenshots of each one and you know taking record of all of the words we've gone through there's also a lot of repetition of each of the words that i've gone through and so to be successful at this specific topic you need to be really well versed in your terminology you need to understand how to use it correctly i hope this video has been helpful to you today and that you use it for your revision and i will see you all again soon bye