 Another group of protostomes are mollusks. Now, mollusks, you should probably be thinking, whoa, holy diverse group, and this is. This group has a lot of different kinds of critters. We have slugs, sea slugs and land slugs. We have different kinds of critters that live in shells like bivalves, snails. This is actually a double mollusk fun time cuddle fest because that's actually a little octopus sitting inside this bivalve shell. I would imagine that the octopus probably yumpsulized the bivalve and then stole its house. I mean, you got to do what you got to do. But cephalopods are squids and octopi and those guys have some unbelievable characteristics. But remember, I don't want you to forget where we are. Remember that in our cladogram, we're just grouping these guys all together as protostomes. So look at, this is actually, what is that thing? An octopus we found at the tide pools in Humboldt County and we actually got to see this thing change color. Like it was crazy talk. Right now it's red. You might be looking at it and going like, sure, red, Wendy. And the next thing I knew, it turned the color of the rock and I got to watch it actually happen. So when I observed this, I don't know, three years ago or whatever it was that I found this awesome little octopus in the tide pools, I thought, how does that happen? How does an octopus actually change color like that? And the fact is it has these little structures called chromatophores and take a second and visualize this for me, okay? They have these little bags of pigment inside their cells. So I've got a bag of, let's say, blue pigment or red pigment. This guy has bags of red pigment that are showing. And there are little muscles that are attached to the outside of the pigment. Can you visualize this? The bag. So here's, oh, yikes, I can't do both. Here's the bag and here's the muscle. When the muscle contracts or shortens, you can't even see that anymore. Here's the muscle contracting or shortening. It's going to pull when it contracts and shortens. It's going to pull the bag into a bigger diameter, which means the bag of pigment is going to take up more space. Can you visualize that? If those smooth muscles relax, the bag of pigment is going to shrink down and be smaller. If the bag of pigment is big, you're going to get a lot of that color. If the bag of pigment is small, you're going to get a little bit of that color. And you can see here, these little muscles, here's the pigment. This is inside a cell, and we're just going to change the size of this. Now, you know that I have to show you a video. A video that I will try really hard not to dance to because, dude, this is so awesome. They put, I don't know how they did this. They put, this is the skin of a squid that has chromatophores in its skin, and they actually zoomed in so that you can see little round circles of pigment. And then they're playing music, and it totally matches to the music, but the chromatophores, like, dance. They get bigger, which means those smooth muscles are contracting, and then they get smaller, which means the smooth muscles are relaxing. Okay, just take a minute to be amazed by this, and then in class, we'll actually watch a video of mollusks hiding, cephalopods, hiding because they've got these unbelievable chromatophores. Okay, get ready to dance. Those are chromatophores. I'm loco. I'm loco. What the heck? Dude. Oh, my gosh. There, little, big, big, and all that is, is contracting. Dude, it's awesome. This lets them change color. You gotta go look up chromatophores on YouTube, and you can literally spend the next three hours just watching all the different videos. It's fantastic. And if you're really motivated, go to the TED Talks, and there's a TED Talk on cephalopods that will blow your mind. We'll watch it in class if you don't go watch it, or if you don't come to my class, then you have to go online to find it because it's really cool. Okay, now we're gonna look at arthropods. This class is so awesome. I mean, every piece gets cooler. Arthropods are amazing. Let's go learn about them.