 So the character that defines everybody that's coming next is it relates to the body symmetry of the animals, and all of them after this point are bilaterally symmetrical. And think about that. All that means is down the midline of a bilaterally symmetrical organism, the critter is the same on each side. So if you think about most familiar organisms, that's totally accurate, like especially vertebrates. They're definitely bilaterally symmetrical. There are some exceptions. If you think about jellyfish, are they bilaterally symmetrical? No, they're round. They're radially symmetrical. So the bilaterally symmetry everybody has. Now we're going to divide off this group that I have labeled protostomes, and you're probably like, what is this protostomy you speak of rigs? Let me tell you, everybody beyond this point has this character called protostomy, protostomy. And pro means first. So I'm going to tell you, there's actually three critters, three groups that we're going to talk about from this point, and I did not plan well here, because look, I'm doing this. There, we'll do that, and then we'll do that. Okay, and all of them are protostomes, and you can imagine that that is distinguished from these other guys who are going to be something that's not protostomes. And I'm going to leave it. You can have a hint by looking at the outline. What do you think those are? But let's talk about what the protostome, deuterostome, what? Why are we even talking about this? It goes back to our blastula. If you look at the development of an animal, you can actually tell a lot of stuff. The blastula changes, right? You don't look like a blastula anymore. You develop over time. And some of the development, some of the stages that you go through as an animal are conserved, so the more closely related you are to someone, the more likely it is that you went through the same process of development. Well, one of the things that happens to that hollow ball of cells is that you get this pore. You get like, like, it's almost like an invagination of the hollow ball of cells. And you can see that happening here. And there's all like holy entire lecture, entire course on embryology and how this happens, which dude's so freaking cool. But regardless, we get this little like hole in that hollow ball of cells. And that hole is called the blastopore, okay? So the blastopore, right? You can imagine, this is my blastopore in my developmental process. If the blastopore becomes the mouth of an organism. So think about this. We indented, we started making this little hole that eventually is going to connect through the other side. What? And you have a hole on one end and you have a hole on the other end, right? And a tube in between, no problem. Well, that actually shows up super early in development. That you have a hollow ball of cells that then creates a hole through the middle like a donut. The hole, the part of the hole that develops first is the blastopore. Now, if the blastopore becomes the critter's mouth, that critter is a protostome. Pro means first. Stome means mouth, mouth first. But the blastopore could have another fate, right? The blastopore could become the other end of the tube, the anus. If the blastopore becomes the anus, then the critter is a deuterostome. I remember deuterostomes had blastopores that became anuses because anuses make doodoo for the deuterostomes. Anuses make doodoo for the protostomes, too. But the anus came first in the deuterostomes. Okay, super cool. So who are these critters that are protostomes? Well, let's lay them out there and then I'll show them to you. So there's actually three groups. We have the anilids, which are segmented worms. We have the mollusks, which are like clams, oysters, octopi, squids. Squids are cool. And then we have one more, one more. Oh, how could I ever forget these guys? The arthropods. I mean, I could do an entire course on each one of these groups. They're so freaking cool. So let's look at the anilids. Segmented worms, great diversity. I want that one. Like, that's a freaking earthworm. It's huge. Earthworms are the most common. Tube worms in the ocean. There's these really cool, like, whatever that thing is that lives in the ocean of polychaete. Those are all anilids. Mollusks, great diversity in molluskland as well. You've got from clams and things like octopi, squids, cuttlefish, nudibranchs, which are sea slugs. These things are so cool. And they can, whatever, I could go on for forever. And then the arthropods. The arthropods have jointed legs. And this is a fascinating fast fact. That almost 80% of all animal species are arthropods. So arthropods are incredibly diverse. You, most arthropods are insects. Insects are freaking everywhere. But look at all those groups of arthropods. And check it out. It includes scorpions. It includes this, like, horseshoe crabs, spiders, ticks. I just have to blow your mind just once. Just once, just once. Take a look at the tick. Point right now to the head of this tick. I know you pointed right here, right? Do you think it has eyes on there? Like, you know, maybe that's an eyeball or that's an eyeball. No, I'm going to blow your mind. You ready? This is almost creepy how this happens. This is actually its mouth. And if you look right here and right here, those are its eyes. So the tick actually inserts its mouth, its entire mouth part into you. And, like, that's what then sucks your blood out. But its eyes are here on the side, like that. Ticks, man. I don't know about ticks. Oh, millipedes. I love millipedes. Centipedes kind of make me go, ee. But millipedes are super cool. My kids used to collect millipedes when we'd go camping. And one time, I don't know, Kai was maybe three or four. He's out there collecting millipedes and he loves all the animals. And he sometimes loved them to death. And the next morning, he gets up and I'm getting him dressed. Like, get out of your jammies, son. Let's go have a day. We're camping. This is awesome. And out of his jammies falls a dead millipede. Like he had been, like, it was in there, in his jammies with him. And I'm sure that he, like, slept on that thing. It did not survive the experience. I don't know how he survived the experience. If I had a millipede, like, in my jammies, I would not, you would see some action. But he apparently was fine with that. All right, crustaceans. What barnacles? These are all arthropods, you guys. Like, this is crazy talk. The salbug or the pillbug or the roly-poly, that thing is the only land crustacean. I mean, tons of parasitic crustaceans. That's, like, a little thing that you can buy that you can, like, grow in your house. Yeah, we've done that, too. My children love animals. And then, of course, you have all of your insects. And insect diversity will blow your mind. So I, what else can I say? I don't know. Let's look at the Deuterostomes next. We know that Deuterostomes have a blastopore that became the anus. And that's how they are classified as Deuterostomes.