Porifera and Cnideria - Video Tutorials & Practice Problems
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Porifera and Cnideria
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Hi. In this video, we'll be talking about porifera and cnidaria, 2 phyla which despite appearances are actually animals. Now, porifera are more commonly known as sponges and they're hermaphroditic organisms for the most part, meaning that they are capable of reproducing sexually, but we also often see, sponges or porphyria reproduce asexually. Now, sponges are filter feeders, meaning that they eat particles that are suspended in water and they're going to do this by actually drawing water through their bodies and we can actually, see a little model of a sponge's body right here and they have this central cavity that's known as the spongicle and this opening through which the water moves, that's called the osculum. Now, the actual inside of the spongicle is lined with these cells called choanocytes, and you can see a choanocyte here, and these are flagellated cells. These cells are what the sponge uses to actually feed on those suspended food particles and also bacteria. And they're going to use their flagella to capture the various, particles and then they're actually going to eat them by phagocytosis, which is that process where they, take the particle into the cell and then they're going to perform intracellular digestion. So unlike you and I who actually digest our food outside of ourselves, right, in our alimentary canals, these organisms will digest their food within the cell in the cytoplasm. Now this gray barrier that kind of separates the red and yellow portions of the sponge's body is known as the meso eel. So that is basically a, barrier that separates or I shouldn't say a barrier. It's it's a demarcator between the two regions of the sponge body and it's basically this gelatinous matrix. It's, you know, kind of ooey goopy stuff. And, the amoebocytes are going to be, very important for the meso eel because they create these rigid structural fibers. Can almost think of it like the the skeleton for the sponge in a sense. They give the sponge body some support structures. They also are responsible for transporting nutrients which is going to be super important for any animal. Now, turning to Cnidarians, these are creatures like jellyfish. Probably a little easier for you to think of them as animals as opposed to sponges which are just so alien it's hard to even think of them as living organisms. Cnidarians are also like very evolutionary mystic organisms. And they're going to have a radial body plan, which remember means that if we were to, sort of like look down on it, we could, divide it into 4 quadrants. This is as opposed to the, bilateral body plan that we'll see, later on down the evolutionary line. Now, their bodies are basically just sacs for their cardiovascular cavity, which is basically the cavity that is going to be responsible for gastro, eating nutrient absorption and vascular, as in transporting stuff around. So basically it's it's the big everything cavity. Again these are super basic organisms, you know, they're not going to have closed vascular systems with, veins and arteries, that sort of stuff, like we do. Now, Cnidaria come in 2 flavors. You can almost think of it. It's more like 2 body plans. You have the polyp, which you can see right here. These are polyps. This is a hydra actually. And basically, the pilot body plan is a sort of cylindrical section which you can see right here and then Let me jump out of the frame so you can see what I'm drawing. And, attached to this cylindrical section and we have these tentacles which are used for capturing prey and also, this segment right here that is responsible for, adhering feed while they're clung to a surface, but they are not sessile, meaning They don't say say sedentary forever like a barnacle or something. They can let go of whatever they're clinging to to, escape a predator for example. Now the other form of Cnidarian that we'll see is probably the form you're more familiar with. This is like what jellyfish look like and this is called a Medusa. You can see, Medusa body plan over here and notice that, it's almost like an inverted polyp. Right? Like the tentacles kind of, or rather I mean like an upside down polyp almost. Right? So the tentacles instead of being on the top side are now flipped under the creature, and so is the, entryway into the GastroVascular cavity. Right? It's on the underside, whereas in the polyp it's sort of on the top side. Now, cnidarians have these specialized cells that are used for what we tend to think of as stinging, right? Jellyfish like sting their prey. Well, there's a little more going on here. These specialized stinging cells are called cnidocytes and they contain a structure called a nematocyst. And basically, this is a, a penetrating barb that can be fired out of the cnidocyte, and, the nematocyst is technically an organelle of the cnidocyte. Its main function is to shoot out that barb, penetrate a, you know, some sort of prey for the cnidarian, and it's going to sting it, immobilize it potentially, and allow the cnidarian to then eat it. Now, these guys, you can tell they are mushy. Right? If you've ever seen a jellyfish washed up on the beach or maybe even floating around water, I mean, pretty clear that these are just like gooey squishy organisms, and that's because they have hydrostatic skeleton. Basically their body is this fluid filled cavity, right, filled with water, and it's surrounded by muscles. So the pressure of the fluid in the body, that fluid pressure actually is what gives the body its structure. It basically, the sort of tension between the muscles and the fluid in the body supports the body almost like a skeleton. Now, the last type of cnidarians I want to briefly mention are called Anthozoa, and these are cnidarians that are like coral and sea anemones. What defines a lot of these organisms or or, something that, you know, we can point to that makes them different from the guys we just talked about is, a lot of them have these endoskelet or rather exoskeletons that are made of calcium carbonate. Right? If you've ever seen a coral reef, a lot of the, stuff in the coral reef has like a hard structure to it. Not all of it. I mean, you know, there's like sea anemones that kinda look like those dudes that flop around it like a used car salesman, lot or something. Anyways, this is just the last type of Cnidarian worth pointing out. These are going to be, you know, look different from the Medusa and, you know, like hydras other forms that we might see. Alright, with that, let's turn the page.