 We humans have a kidney for excretion. Our kidneys are efficient in filtering out all the waste from our body. And this is also true for all the vertebrates. All vertebrates have kidneys. But when we talk about the invertebrate world, we get to see a diverse kind of excretory system. And invertebrates are simple organisms, right? So their excretory system is also very simple. Talking about the simplest protozoa, the amoeba, they just diffuse out all the waste that is produced inside the cell. Because they are single-celled organisms, right? We cannot talk of special structures inside them for excretion. Because they themselves are just single-celled organisms. But as the complexity of the invertebrates increased, we started seeing special structures for excretion. And the very first structure appeared in platyhelmets. Platyhelmets we know are flat worms. They could be endoparasites or free-living. And their special structure for excretion is called a flame cell. Or we also call it protonephridae. And this is how a single cell looks like, okay? This is the nucleus. The black dot is the nucleus. And the white thing that's hanging down here are cilia. Let me label it. These are cilia. And this complete structure is called a flame cell. And where are these flame cells located? Well, they are located on the entire body on the literal sides. On both the sides, you will see flame cells lining on the body of all platyhelmets. Now, how do they function? Well, the upper part of this flame cells are towards the inner part of the body. It is placed like this, okay? And this broader part, it collects ammonia and waste products from the body fluid and sends it down through this canal kind of thing and leaves it into the excretory duct, okay? So all the flame cells will collectively remove the waste from the body and will release it into the excretory duct. So this is the excretory duct. Now, talking about how it got the name the flame cell. Well, when the waste gets into this flame cells, the cilia here, they help the liquid to go down into the excretory duct. And while doing so, the cilia moves so fast that it looks like a flickering flame. And that's how it got its name, the flame cell. Well, coming to the next name, protonephridae. Why is it called so? Well, that again has another story. If you look at the flame cells, you will see that it has no opening towards the inner side of the body to collect the waste, right? All the waste or water or ions get into the flame cell through diffusion. And such excretory structures are called protonephridae. But as the complexity of organism increases, as we move from pletihelminth to anelids, we will see that they have excretory structures that has opening on both the sides towards the inner body surface and also an excretory pore. So such excretory structures are called nephridae. But since flame cells don't have any such opening, it is called protonephridae, okay? Now again, here we have taken the example of planaria, which is a free-living, aquatic pletihelminth. And since it has abundance of water in its surrounding, it can afford to excrete ammonia. But there are endoparasites as well like tape, warm or fluke, which are also pletihelminth, right? And they do not have enough water in its surrounding to excrete ammonia. So they excrete urea, okay? So pletihelminthes can both be ammonotelic and ureotelic, okay? And again, these flame cells, flame cells or protonephridias, they not just help in excretion, but they also help in maintaining the fluid balance and ionic concentration inside the body, right? So we can say that they help in osmoregulation of the body, right? Okay, so this was about the excretory structures of pletihelminthes. Now let's move towards a little more complex organism, which is anilids, and we will look at the excretory structure of the earthworm. Now if you look at the earthworm closely, you will see that it has segments in its body, right? And each segment, or I should say most segments, except for very few, they have their separate excretory structure. I mean whatever waste is produced in each segment, it has a structure that throws out directly from that particular segment, okay? And that structure is called nephridia. Now here is a thing to note. Few anilids can also have protonephridia in their body, but most anilids, they are seen to have nephridias. And this is how a single nephridium looks like, okay? Now let's talk about how it functions, okay? As we discussed, each nephridium is present in a single segment of earthworm, right? And the opening, the funnel-shaped opening, is towards the body cavity or the silo, right? And this funnel-shaped opening is called a nephrostome. And as you can see, it has cilia surrounding it. This cilia helps to bring in the fluid into this nephrostome, okay? And the nephrostome proceeds towards this funnel kind of area, which is also called the neck. The neck also has cilia inside it, right? They help to send the fluid down towards the rest of the coiling part of the nephridium, okay? Now here I have made just three loops in the nephridium, but in reality it is highly coiled, very highly coiled, okay? And this coiling or the length of the nephridium actually helps in reabsorbing the water and ions into the body of the earthworm, okay? So whatever important ingredients were sent out is actually reabsorbed in this coiling part. And whatever remains, it proceeds through the slope and gets out of the body of the earthworm through a pore, which we call the nephridiopore. So this nephridium, the excretory structure of anelida, it helps in excreting the nitrogenous waste and also helps maintain the body fluid and ilic balance, that is osmoregulation, okay? And just like pletihelminthus, even in anelida if there are enough water in its surrounding, they will excrete ammonia, they will be ammonotelic, and if they have less water in their surrounding, the nitrogenous waste will be urea and they will be ureotelic, okay? Now let's talk about the excretory structures of orthropoda. Here is our mosquito, for example, and these tubes hanging from the gut or the elementary canal of the mosquito, these are the excretory structures of the orthropoda and they are called malphigian tubules. And where exactly are they present in the elementary canal? Between the mid-gut and the hind-gut, okay? And they look like finger-like projections and they could be present between 60 to 150 in numbers. Now let's talk about how do these malphigian tubules function. So here I have enlarged a single malphigian tubule and as you can see, it is open only towards the gut area, only towards the elementary canal, right? Now we know orthropodes, they excrete uric acid, right? In the form of pallet or a paste and they do that by sending out the uric acid into these malphigian tubules, along with water, ions and all the stuff that's in the hemolymph. They don't have red blood like us, they have hemolymph. And from the hemolymph, the uric acid, water and ions. They are all sent out into the malphigian tubule, okay? Now as the uric acid gets into these malphigian tubules, the pH here is acidic and that precipitates the uric acid in the malphigian tubule, okay? And that is how we get a paste or pallet kind of excreta from orthropodes, okay? And whatever important stuff that was sent into the malphigian tubule like water, ions are absorbed back into the body. So this is how the malphigian tubule works and that is how orthropodes excrete. Moving ahead, let's talk about the excreta system of crustaceans. And here is an example of prawn, which is my favorite seafood and this is often cooked at our place, okay? And I often see my mom cutting and cleaning it properly before they are cooked and she particularly cleans the head area really well. And later in life, I understood that crustaceans, they pile up their waste somewhere in the head area underneath the antenna, okay? And upon closer look at their excretory part, it would look somewhat like this and we call it the green gland. And they are called green gland because of this green portions that you see, a pea-shaped portion which is green in color and that's why the whole thing is called the green gland, okay? And these two are present on either sides of the prawn, okay? We have a pair, we can say. And this is not the end of the excretory part, okay? These two parts, they extend down into a sac kind of thing, but we will not discuss about that in this video. We will only limit our discussion to these green glands, okay? So the green gland composes of this part called the end sac. Then attached to the end sac, you have these tubular connection-like thing, which we call the labyrinth. Now let's talk about how they function, okay? So crustaceans, they have hemolymph, right? So the nitrogenous waste is all absorbed into the labyrinth and the end sac, okay? And the nitrogenous waste and all other waste produced inside the body goes down the labyrinth into this, this part, which is called the bladder. And the excretory portion is all stored in the bladder before they are excreted out through these pores that you see. These pores are called ureter. Ureter or excretory pore, okay? And these are present underneath the entenal coxa. And that's the reason this green gland is also called entenal gland. And again, since crustaceans or prawns, they are present in abundance of water. They are aquatic. They excrete ammonia and they are ammonotelic. And this is their excretory structure. So in this video, we'll look at the four special excretory structures of invertebrates. The flame cells, malfeasant tubules, nephridia and green glands or entenal glands.