 So we know that what we're dealing with next, we talked about protostomes and branched them off, and now we're going to look, everything beyond that we're going to look at is a deuterostome, D-E-U-T deuterostome. Deuterostomes, the blastopore becomes the anus, and there are two groups of deuterostomes that we're going to look at. The first group, and we're going to spend a little bit of time right now talking about them, are echinoderms. And probably our quintessential group of echinoderms would be like C-stars. But then the other group of deuterostomes are the chordates. And chordates, we're going to talk about in the next lecture. Chordates include vertebrates. All chordates at some stage in their life cycle, have what's called a notochord. And the notochord is a structure that in some critters becomes the, really, I want to say vertebrae, but it's not the vertebrate, the spinal cord. I think it was somewhere in there. It's embedded, or it's protected by the vertebrae. So, okay, so the notochord is the pre-vertebrate structure. But there are invertebrates in the chordates. So not all chordates have a vertebral column. So, but they all have a notochord and they all are deuterostomes. Echinoderms are deuterostomes that do not have a notochord. And you know what, this is really interesting. And this is a good example of a characteristic that disappears and then comes back. They are radially symmetric. And if you think about when did we last see radial symmetry with our jellyfish, with our whole Nigerians, those guys, they were radially symmetrical. We could group jellies and echinoderms together because they're all radially symmetric. And that might be a way that we would group them if we didn't know better. Knowing about their embryology, knowing about their development and other characteristics of complexity and organ structure, that tells us that no, echinoderms probably are more closely related to chordates than they are to say mollusks and arthropods and other protostomes. All right, so let's take a look at a little bit of echinoderm diversity. Let's include the C stars. You might be questioning like what are these guys doing. This is actually an example of what's it called when you eat people of your... cannibalism. That's what's going on here. Urchins are echinoderms. This is a C cucumber. C cucumbers are fantastic. They're the critters that we told you about that squirt their guts out if they are feeling endangered. They'll squirt their guts out and try to scare off the bad guys that are coming to get them. Sand dollars are living echinoderms. And you can see they look kind of spiny. They definitely have like this similar radially symmetric structure. Echinoderms C stars have unbelievable strong muscle. They can actually open up like some kind of a bivalve. They then barf out their stomachs and stick their stomachs into the thing that they want to digest. So if you imagine opening up a clam, the C star will actually insert its stomach into the clam shell and digest the clam on the outside and then suck all the digested gut parts back inside. So here's a kind of C star called a brittle star. This was actually a brittle star we found at the tide pools here in Humboldt County. So we can actually see these things. You notice like the little more defined center body part. That's what indicates a brittle star. But there is a significant amount of diversity with the echinoderms. And in the next set of lectures, what we're going to look at are the chordates. So we're going to flesh them out. I've named this lecture the invertebrates and the next one vertebrates. But we're going to have a few invertebrates left over to talk about with the vertebrates. So that will give you some orientation of where we're headed. So I'm just going to circle it because I'm going to circle it in yellow because yellow is my favorite color. This is where we're going next. All right, how awesome is this lecture? Vertebrates coming at you.