Invertebrates and Chordates Overview

Hello, BISC-132. This is the beginning of Recorded Lecture 3-5. Continuing on with invertebrates. We're going to finish up, I promise. So, last time we had started talking about arthropods, and we'd gotten to the point where we were going through specific subphylas. So, up next is subphylum hexapoda. So... Pota means foot. We've seen this many times. Hexa, like a hexagon, has six sides. Hexa means six, so six foot. These are insects. And I said that arthropods is the the largest phylum of all animals. This is the largest subphylum within Arthropoda, so obviously there's a lot of stuff here. I want you to be familiar with these if you're not already as insects. ants, beetles, cockroaches, butterflies, crickets, and flies. And again, that's not, you know, naming all of them, just some of the more prominent ones. They're known for having three tagmata. We mentioned this in the sort of generic arthropod, which turns out to be a hexapod, a bee, head, thorax, abdomen. And many of the members have wings. So yeah, I didn't see any crustaceans with wings or spiders with wings or centipedes with wings, but Wings are something that we definitely see in a lot of hexapods and that's part of, you know, the secret to their success, being able to live in all these other different ways that we couldn't see in the other subphyla. And another thing that we see a huge diversity among hexapods that allow them to be such a large subphylam has to do with their mouth parts. Don't sweat the details down here. But what this is showing in kind of a color-coded fashion is, again, the secret to success is taking a body that is modular and has lots of... of different parts that can be modified to do different things. So you know you can take these same basic mouth parts and create a mouth that's good at siphoning up nectar like a bee or great at lapping up you know chewed up grass stuff like a grasshopper or you know with a long um maxillae in order to get nectar deeper within a flower or piercing skin to get blood like a mosquito and of course many many others these are all just sort of illustrating in the point that within subphylum hexapoda, they've got mouth parts that can easily be modified for diverse feeding strategies. That's a great way to evolutionarily radiate out and speciate out if you can be modified to do a lot of different things. Another thing that's distinctive of this subphylum is metamorphosis. So all arthropods have to molt, but many of them just molt to grow larger. What we see in... insects, in hexapods, is actually changing the form of their body and gaining new abilities or new parts during this molting. So there are two types. The complete metamorphosis is what we see in a butterfly, for example, where you have a larva form that forms a pupa and then comes out as an adult. It looks completely different. The other type of metamorphosis called an incomplete metamorphosis is where you... you have a series of molts where, you know, it's growing and changing a little bit each way, and as an adult, it ends up being different from the first form, but it wasn't a single dramatic molt that changed things. For example, the grasshopper here has wings, and the earlier nymphs did not. So my summary here, many hexapods undergo metamorphosis as part of their molting in order to not just grow larger, but to actually alter their body. body. Okay. And with that, we're done with arthropods. And this is another, you know, a major milestone here. We're done with protostomes. So we're done with this clade protostomia. which means all we have left now are these deuterostomes. And yeah, if you've forgotten this, protostomes were the mouth first, deuterostomes were the anus first. Go back to the last chapter if you want to have an explanation of this again. But yes, we are now moving on to superphylum deuterostomias. So these two, chordates and echinodermata. So much smaller than protostomia, but as it turns out, this one's going to be bigger than it looks. Anyway. So, clade deuterostomia, these are called deuterostomes, and yes, I can safely say this is going to include all further groups that we will talk about. Let's start with the echinoderms, with phylum echinodermata. So, clade deuterostomia, phylum echinodermata, this is going to be sea stars, or starfish, if you will. Brittle stars, sea urchins, sea cucumbers. yeah all this stuff so sea stars sea urchins sea cucumbers and brittle stars they are and i can you know a lot of times i have to say oh they're mostly this or they're primarily this because it feels like there's an exception all the time but uh you can confidently say every single aquino derm is not just aquatic but marine all salt water no fresh water echinoderms no terrestrial echinoderms so they've they found their niche um they are sea laminates uh and What's interesting is, you know, we've been... you know, breaking down in this table here, coelomates and pseudocelomates and acelomates and everything. But what I'm pointing out now is that if you wanted to draw a circle around, you know, what a coelomate is, it would be something like this. So there are some protostomes that are coelomates and some that are not. And all deuterostomes, incidentally, are coelomates. But the point is that the C... coelom within deuterostomia that we find in chordates and in echinodermata, it evolved independently of the coelom in arthropods, which evolved independently of the coelom in these, you know, few Lophotrochozoans that are coelomates. So coelomate is not a clade. It's one of those paraphyletic groups because it's not an ancestor in all its descendants. So So, yeah, echinoderms are coelomates. The coelom evolved independently of the coelom in any of these other groups. Coelomate is not a clade. Okay, so going back to this. Yep, remember we're doing deuterostomes for the last two. Body cavity coelomate and circulatory system closed. We'll get to that in just a minute. But before that, let me go back to this point. I had already filled this out. one of the things I said way back when we got to this point was that all further groups were going to have bilateral symmetry. Well, all further groups includes echinoderms. And if you remember, bilateral symmetry is supposed to mean one plane down the middle dividing into mirror halves. And if you think about it, one of the most famous echinoderms, the starfish or the sea star, doesn't seem to have that. So it has what's called pentaradial symmetry. So what gives? What's up with that? Yes, they are members of this group, Bilateria, because they have bilateral symmetry as larva. So, okay, so here is a young sea star with very obvious, you know, single plane down the middle bilateral symmetry. It is as an adult that they develop into. this penta-radial symmetry. So don't have to redo this phylogenetic tree. We're off on a technicality and it makes sense. Some members have bilateral symmetry as larvae, but develop penta-radial symmetry as adults. So we've covered all our bases there in case there was any confusion. So let's take a look at their anatomy. So again, we're using a C-star as a generic example here. But again, there are other echinoderms. We're just trying to keep things simple here. One of the things we see in the C-star is with several of the organ systems, they exist in a central ring, whether it's the nervous system or whether it's the digestive system or whether it's... It's this water vascular system that we'll talk about in just a minute that exists in sort of a central ring and radiate out to each of the arms. So this is kind of like those, you know, segmented worms that had a little bit of everything in each one of their segments. Well, the sea star has a little bit of everything in each one of its arms, which is why if an arm becomes detached, you know, ripped off in battle or something like that, it can grow into a new individual because it has a little bit of everything. It has everything it needs. So, organ systems radiate out to the arms from a central ring. Another thing to point out about echinoderms is their skeleton. We've been talking skeleton in most of these groups. They have an endoskeleton. So if you see a sea star like this in a beachside gift shop or whatever, that's the skeleton of a sea star. Some of them, you know, more gnarly looking than others, especially on, you know, a microscopic level. This is a skeleton made of primarily of calcium carbonate. And again, this is an endoskeleton. It's the... inside as opposed to those exoskeletons that we saw with arthropods which were sort of outer armor. Okay now the water vascular system. So this is something that is you know completely unique to this group and quite frankly kind of weird. So the way echinoderms move is through these tube feet. And the way these tube feet are powered is hydraulic pressure. So to go back to this anatomy here, here is, you know, the water comes in in this central part. It radiates out through these arms. And with small muscles, they can control how much of this pressurized fluid goes into these tube feet and how much, you know. stays out of the tube feet in order to extend them and move them around and to crawl around. Now that's not all. In addition to using this water vascular system for, you know, moving for locomotion, for grabbing prey and manipulating them. This water vascular system also functions as a circulatory system. So this is why I wrote closed. It's not a traditional closed circular. circulatory system with true blood, like we see in other animals that have closed circulatory systems. But really, it's unique. But it's probably more appropriate to call it closed than it would be to call it open if we're trying to keep things simple. So here's my summary of all that. Phylum Echinodermata members have a unique water vascular system. This is formed from the phylum, so they're using this body cavity to do this. It uses hydraulic pressure to power movement of these tube feet. It's used for locomotion and prey manipulation, and also functions as their circulatory system. Okay, well, that does it for echinoderms. Now there's just one group left, phylum chordata. And so it's actually at this point that we have to transition to the next chapter, which is entitled vertebrates. Now, It's called vertebrates, but we're actually not on vertebrates yet. We actually have to talk about chordates before we can get to vertebrates. So it's kind of a weird way to transition the chapters, but it is what it is. So, OK, what is a chordate? Well, chordates have. These five features, I've highlighted one of them here, but only four of them are drawn. There are five features that distinguish, that are unique to chordates. One of these is something called the notochord. This is a flexible rod that supports the body that, you know, in some members can, you know, form a skeleton, act as a skeleton. But in the basic chordate, it's just a nerve chord. So there we go. This is still clade deuterostomia, phylum chordata. Members have five features. And this is sort of an important parenthetical point. They have... all chordates have these five features at some point during their development. We're going to see it is very possible, and we see this within our own bodies, for these features to be lost, but they're all seen at some point during development, even if they're not present in the adult. So, okay, feature number one, notochord, a flexible rod that supports the body. Okay, in addition to that, we have the dorsal hollow nerve chord. So, this is a Also dorsal here along the back. This is a nerve cord and it relays information. This forms the spinal cord and the brain in humans, for example, but it doesn't have to be that sophisticated. Pharyngeal slits or pharyngeal pouches are located near the mouth. And these are used to help in filter feeding. This is definitely one of those features that has been lost or certainly. reduced in function. It is not used for filter feeding in humans. But, you know, if you look at embryology, if you look at human embryos, this is present at certain very, very early stages. Because, yeah, just to let you know, humans are going to be coordinates, of course, because we haven't come to ourselves yet. So pharyngeal slits, openings behind the mouth can be used to filter feed. And finally, the fifth feature, which wasn't labeled in this original figure, but I sort of drew a picture around it here, something called the endostyle. This is a mucus-producing tissue that also aids in filter feeding, and it's another thing that humans don't have apparent. Oh, sorry. Turns out I can't count. This was only number four. Number five is the post-anal tail, a tail that extends past the anus. So. This is another thing that humans have lost, but we have during our embryonic development, this post-anal tail, tail extending beyond the anus. So we can also say if we want to finally finish this table here, that chordates are coelomates and we have a closed circulatory system. So that lets us finally finish out this table. And again, It seems like a phenomenal amount of information, but, you know, for most of these things, they're all bilateral except for a couple. They're all triploblasts except for a couple. you know, the protostome, deuterostome is easy enough, and then it turns out to not be that much information about remembering which ones are acelamates, pseudocelamates, selamates, and the circulatory systems of each of these groups. So this does not have any new information. Everything on here I've mentioned throughout, you know, last chapter, and this one on, you know, these slides that I have text, but, you know, this is just a convenient way if you want to screenshot this or whatever, or draw this out yourself. to just organize all of this information. So now that we know what it means to be a chordate, on to the vertebrates, right? I mean that's what the chapter is called, vertebrates. Well actually we can't get there yet. As it turns out, all vertebrates are going to be chordates and you know have these chordate features, but there are actually two groups of animals that are chordates. They are members of this phylum chordata, but they are not vertebrates. They don't have a skull or a spine or things like that. we don't want to call these invertebrates because invertebrates typically refers to, you know, all of this other stuff, all the phyla that are not chordates. But we can't call them vertebrates either. So these two weirdo groups that are chordates but not vertebrates are referred to as non-vertebrates. Sorry if that's confusing terminology, but I don't make this stuff up. So what are these weird non-vertebrates? Well, one of these is subphylum, and yes, it's a subphylum because this is underneath phylum chordata, subphylum cephalocordata. Members are called lancelets because I guess they kind of look like a little lance, whatever. These look like fish, but if you examine them more closely, they're definitely not fish. They don't have any... any bones they don't have a skull they don't really have a well-defined head you know they certainly don't have eyes or or teeth or any of that stuff they definitely have all the apparent chordate features they got the pharyngeal slits the post-anal tail they you know they have the dorsal nerve cord and notochord and the endostyle they got all this you know chordate stuff but You know, they are definitely not vertebrates. These are filter feeders that bury themselves in, you know, sand or rock and, you know, filter particles out of the water. So not much to say about them. Subphylum cephalocordata. Lancelets, Filter Feeders, and these are one of those two non-vertebrates. The other group of non-vertebrates is Subphylum Urocordata. Members here are called Tunicates. and man these things are weird looking so this includes bluebell tunicates and this looks like a heart uh at the bottom of the ocean uh this this sea squirt um these are really weird because this thing doesn't look like it has any of those chordate features, certainly not things like the dorsal nerve cord. It doesn't look like it has, you know, a mouth and an anus, this sort of tube-shaped body. Well, that is because it has lost these features. during its development. So if you look at one of these tunicates in its larval form, okay, you can see all this. You can see the pharyngeal slits here. You can see the anus. You can see the notochord and the dorsal nerve cord. It's as an adult that it takes on a very different shape and loses a lot of these features, but has the body plan that it has as an adult. And again, is a filter feeder. So the larvae have chordate features, most are lost in adulthood. They're filter feeders. Most of them are sessile, you know, attached to rocks or something in a filter feeding. But there are actually some really cool salps, is what they're called. Might be confused for a jellyfish, a sea jelly. But this is a chain of colonial tunicates that, you know, exist within the ocean floating around. And being a filter feeder. But either way, some grow in long chain colonies, but at the end of the day, they're still filter feeders. So, okay, those two subphyla were what we call nonvertebrates. Now we're on to actual vertebrates. This is a subphylam underneath phylum chordata, subphylam vertebrata, also known as craniata. And so, you know, It's one of those terms that's sort of embedded in our collective consciousness that these are vertebrates. We should call them vertebrates. It's vertebrata. But as we're going to see, the cranium actually came first. So craniata might be a better name for this, but right now they're kind of used interchangeably. Members of this subphylum are called vertebrates. And again, the first evolutionary innovation was the head and the skull. which protects the brain. We definitely don't see that in in tunicates or or lancelets here. And vertebrates, this subphylum is going to include all further groups. So at this point, I want to introduce a new phylogenetic tree. I made this myself. It does not include everything, but it includes a fair amount of stuff. There's a chordate ancestor here working up in a stepwise fashion. So let's start by talking about fish. Well, okay, where are fish? Well, there's... bony fish but these are some lampreys these are also fish fish is a paraphyletic group fish the things that we call fish that is not a single clade it is not an ancestor in all of its descendants it's several clades that we sort of lump together we exclude all the other vertebrates to to create this group so fish is not a clade it's a paraphiletic group but you can't not have fish it's a it's a term that still exists uh even if it's even if it's not a clade so most fish are uh ectotherms so this is a new term at this point it's uh defined within the key terms, sometimes colloquially called cold-blooded. The formal definition of ectotherm is an animal incapable of maintaining a relatively constant internal body temperature. So they rely on their environment for their body temperature, and we'll see this again in other groups, but yeah, just introducing this because it's the first time we've seen this. Okay, so the simplest of fishes is a group called hagfish. these are limbless uh kind of look like an eel but you know eels are going to be very different uh these are limbless scavengers and you know here's a picture that maybe shows this a little bit better um they'd have a skull uh but no vertebrae so again the skull evolved first so these are the uh most ancient living fish uh because they're at this you know primitive stage where they have a skull but not any vertebrae yet. These are sort of eel-like, just referring to their limblessness scavengers. Okay, our next evolutionary innovation after the skull is the vertebral column, the spine. So we see this in the next group of fish called lampreys. Here's a cartoon of a lamprey. Here's some other drawings of lampreys. Here are some terrifying photographs of lampreys. Actually, that's... a fish there's the lamprey uh attached to it um and yeah they do have a skull they do have vertebrae uh they don't have a jaw uh so they they have these teeth that you know they use to attach themselves to their hosts these are all either filter feeders or parasites so without a jaw they they can't really be hunters or carnivores but they can definitely be parasites and filter feeders so lampreys have a skull and a vertebral column. And yeah, noting that these vertebrae, that's a replacement for the notochord. Again, the job of this is to protect that spinal cord, doing the bone here, doing a much better job of that than the notochord, sort of an extension or growth of that. And again, no jaw, we'll see that soon enough. Lampreys are parasites or filter feeders. Okay, so they don't have a jaw. You can probably guess what the next major evolutionary innovation is. A jaw! And so the clade that we're in now is called Natostomata. And this is a clade that can be called jawed vertebrates. So notice it's not jawed fish, it's jawed vertebrates. So the evolution of the jaw is something that happened in early fish, but it's something that's passed on from fish to all of their descendants, onto amphibians, mammals, reptiles, birds. So this clade of gnatostomata, jawed vertebrates, this includes everything to come. We are jawed vertebrates, obviously, with our jaw. So they have a skull, a vertebral column, and a jaw. And again, this is a big deal. The jaw enables for additional modes of feeding. You can chew up food, you can hunt prey more effectively. Yeah, this is big. There's a reason why virtually all vertebrates alive today have a jaw in one form or another. Okay, so our next group, again we're under this umbrella of jawed vertebrates, is a class called class Chondrichthyes. This includes sharks, rays, and skates. These are sometimes called cartilaginous fishes, because, I mean, you can't really tell by just looking at this skeleton, but it's made out of cartilage. We have cartilage, you know, in our earlobes and in our nose. Instead of having a heavy bone skeleton, they have a more lightweight, flexible cartilage skeleton. So, chondrichthys, cartilaginous fishes. sharks and rays. So they're called cartilaginous because they have a cartilaginous skeleton, not made out of bone. It's lightweight, but it's not as strong as bone. So there are going to be some upsides and some downsides to this, and there's going to be, there are some reasons for this. A lot of these need to move to not sink. That means they don't have a good physiological solution to, you know, affect their buoyancy. So the way to not sink to the bottom is to keep moving. And in fact, a lot of these have to keep moving to keep breathing. These sharks called obligate ram ventilators. So they need to constantly be on the move. And if you have a really heavy skeleton, that's burning a lot of energy if you have to constantly be moving to either breathe or to not sink. So that's the reason for the lightweight cartilaginous skeleton, because again, it's definitely not as strong as bone, but it cuts down on the amount of energy you have to spend to move around. And yeah, a lot of them definitely have to move around to avoid sinking or drowning, essentially, if they don't get new water on their gills. So the light skeleton reduces energy spent in movement. There are some features here that we don't want to discount. Paired fins uh doesn't seem like a big deal but you know this is definitely an upgrade over these limbless lampreys and the the limbless hagfish uh so having you know paired fins one on either side of the body is is a is a big thing that we're going to see in pretty much all further groups as well most can drink these are marine and as we know most of these are carnivores so uh there are so this is a this is a class If we want to talk about the rest of fish, that's actually not one class. There are several different classes of what we collectively call bony fishes. So this is a, I'm not going to break things down to the class level, although the classes certainly exist. I'm going to lump together all the fish with bones into a clade called clade osteichthys. So these are called. the bony fishes. And yep, they're named appropriately. They have a skeleton that's not made of cartilage, but is made out of bone. And again, it's the exact opposite of cartilage, which was lightweight, but weaker. The bone skeleton is heavier, but stronger. So this is accompanied by a couple of evolutionary innovations that help them, you know, not sink. The weight of this heavy bone skeleton is offset by air. in a structure called a swim bladder. Chondrichthys do not have this, only bony fishes have this. The swim bladder is an organ that is attached to the circulatory system. gases can be put into the swim bladder or taken out of the swim bladder allowing the fish to to regulate its its buoyancy and so it can stay at a certain level in the water and not sink even though it has a heavy bone skeleton so this again this sort of goes together with the bone skeleton the swim bladder allowing it to maintain its desired buoyancy another feature that kind of goes with this heavy skeleton is a structure structure called the oparculum or gill cover. So one of the things that we saw in sharks were, you know, their fin or their gills, you can't see them very well here, their gills are just sort of exposed to the surrounding water. Many of these, like this shark, have to keep moving to expose their gills to new water. Of course, that takes a lot of energy to keep moving. If you have a heavy bone skeleton, you want to avoid having to move constantly. The operculum or the gill cover is a cartilaginous flap that not only protects the gills, but has muscles attached to it so it can flap back and forth, circulating water over the gills, allowing this fish to breathe, to have new water exposed to its gills without having to swim around constantly. So this... This is also sort of related to the heavy bone skeleton offsetting the weight of that by not having to move all the time. So members of Cladosteichthys have an operculum, or a gill cover, that protects the gills and helps pass water through the gills. Now... There are, sorry, I think I said a minute ago I wasn't going to get into the classes. I lied. I'm not getting into all of the classes because several of them are extinct. There are two extant classes, meaning not extinct, that are members. of this clade of bony fishes. The biggest one by far is class Actinoptergii. It's quite a mouthful, Actinoptergii. These are called, yeah, these include... virtually all bony fish that you can possibly try to think of. It's going to be easier to remember the like two bony fish that exist today that are not members of this class. Members of class Actinoptergii are called ray-finned fishes. Again, this is within clade osteopthes class Actinoptergii ray-finned fishes. This includes almost all bony fish alive today, and they're called... ray-finned because their fins are webs of skin with thin spines. So here's a cartoon of this. Yep, there's one of the fins. And yeah, there's some bone here, but most of the actual appendage is just this flat, thin ray. It's not a very robust appendage. It works just fine for them. They're extremely successful throughout the planet, but yeah, their fins are pretty simple. In contrast, the other class of living bony fishes is class Sarcopturgii, and this only has a couple of members, a few species of lungfish and the coelacanth. These are known as lobe-finned fishes, very few living members. And obviously the difference here is in their fins. Instead of being thin rays, these lobe-finned fishes have much more robust fins filled with bones filled with their own muscles the fins and rayfin fishes are attached to the shoulder basically and they use shoulder muscles to move back and forth here there are muscles within the the appendage within the the fin itself so this is worth pointing out and this is worth uh you know bringing up these muscular bony fins possessed by class sarc coptergii because what we're going to see is these are the precursor to the weight-bearing limbs of all further vertebrates. So these are the ancestors to what would become amphibians and then mammals and then reptiles and then birds. And again, you can track these synapomorphies to go back to that term from the very first lecture in the quarter. The bones in these... these lobe-finned fishes correspond to bones of living land vertebrates and other extinct links between them and the land vertebrates that exist today. Again, evolution is all about taking something that already exists and modifying it. And so if you have a limb that's filled with muscles and bones that can be modified to form a limb that can bear weight on land and that is what the evidence points to so the fins of these sarcoptergii evolved into the limbs of all further vertebrates and we'll talk about all further vertebrates uh in the next lecture so this is typically my cut off at the end of fishes before we get into the rest of vertebrates this is the end of recorded lecture three five This is also the cutoff for exam number three. So we'll get into amphibians, birds, and mammals, and all that fun stuff for the fourth exam. This is the end of exam three stuff.

So, up next is subphylum hexapoda. So... Pota means foot. We've seen this many times.

Hexa, like a hexagon, has six sides. Hexa means six, so six foot. These are insects. And I said that arthropods is the the largest phylum of all animals.

This is the largest subphylum within Arthropoda, so obviously there's a lot of stuff here. I want you to be familiar with these if you're not already as insects. ants, beetles, cockroaches, butterflies, crickets, and flies.

And again, that's not, you know, naming all of them, just some of the more prominent ones. They're known for having three tagmata. We mentioned this in the sort of generic arthropod, which turns out to be a hexapod, a bee, head, thorax, abdomen.

And many of the members have wings. So yeah, I didn't see any crustaceans with wings or spiders with wings or centipedes with wings, but Wings are something that we definitely see in a lot of hexapods and that's part of, you know, the secret to their success, being able to live in all these other different ways that we couldn't see in the other subphyla. And another thing that we see a huge diversity among hexapods that allow them to be such a large subphylam has to do with their mouth parts.

Don't sweat the details down here. But what this is showing in kind of a color-coded fashion is, again, the secret to success is taking a body that is modular and has lots of... of different parts that can be modified to do different things. So you know you can take these same basic mouth parts and create a mouth that's good at siphoning up nectar like a bee or great at lapping up you know chewed up grass stuff like a grasshopper or you know with a long um maxillae in order to get nectar deeper within a flower or piercing skin to get blood like a mosquito and of course many many others these are all just sort of illustrating in the point that within subphylum hexapoda, they've got mouth parts that can easily be modified for diverse feeding strategies. That's a great way to evolutionarily radiate out and speciate out if you can be modified to do a lot of different things.

Another thing that's distinctive of this subphylum is metamorphosis. So all arthropods have to molt, but many of them just molt to grow larger. What we see in... insects, in hexapods, is actually changing the form of their body and gaining new abilities or new parts during this molting.

So there are two types. The complete metamorphosis is what we see in a butterfly, for example, where you have a larva form that forms a pupa and then comes out as an adult. It looks completely different. The other type of metamorphosis called an incomplete metamorphosis is where you...

you have a series of molts where, you know, it's growing and changing a little bit each way, and as an adult, it ends up being different from the first form, but it wasn't a single dramatic molt that changed things. For example, the grasshopper here has wings, and the earlier nymphs did not. So my summary here, many hexapods undergo metamorphosis as part of their molting in order to not just grow larger, but to actually alter their body.

body. Okay. And with that, we're done with arthropods.

And this is another, you know, a major milestone here. We're done with protostomes. So we're done with this clade protostomia. which means all we have left now are these deuterostomes.

And yeah, if you've forgotten this, protostomes were the mouth first, deuterostomes were the anus first. Go back to the last chapter if you want to have an explanation of this again. But yes, we are now moving on to superphylum deuterostomias. So these two, chordates and echinodermata.

So much smaller than protostomia, but as it turns out, this one's going to be bigger than it looks. Anyway. So, clade deuterostomia, these are called deuterostomes, and yes, I can safely say this is going to include all further groups that we will talk about.

Let's start with the echinoderms, with phylum echinodermata. So, clade deuterostomia, phylum echinodermata, this is going to be sea stars, or starfish, if you will. Brittle stars, sea urchins, sea cucumbers.

yeah all this stuff so sea stars sea urchins sea cucumbers and brittle stars they are and i can you know a lot of times i have to say oh they're mostly this or they're primarily this because it feels like there's an exception all the time but uh you can confidently say every single aquino derm is not just aquatic but marine all salt water no fresh water echinoderms no terrestrial echinoderms so they've they found their niche um they are sea laminates uh and What's interesting is, you know, we've been... you know, breaking down in this table here, coelomates and pseudocelomates and acelomates and everything. But what I'm pointing out now is that if you wanted to draw a circle around, you know, what a coelomate is, it would be something like this. So there are some protostomes that are coelomates and some that are not.

And all deuterostomes, incidentally, are coelomates. But the point is that the C... coelom within deuterostomia that we find in chordates and in echinodermata, it evolved independently of the coelom in arthropods, which evolved independently of the coelom in these, you know, few Lophotrochozoans that are coelomates.

So coelomate is not a clade. It's one of those paraphyletic groups because it's not an ancestor in all its descendants. So So, yeah, echinoderms are coelomates.

The coelom evolved independently of the coelom in any of these other groups. Coelomate is not a clade. Okay, so going back to this.

Yep, remember we're doing deuterostomes for the last two. Body cavity coelomate and circulatory system closed. We'll get to that in just a minute. But before that, let me go back to this point. I had already filled this out.

one of the things I said way back when we got to this point was that all further groups were going to have bilateral symmetry. Well, all further groups includes echinoderms. And if you remember, bilateral symmetry is supposed to mean one plane down the middle dividing into mirror halves.

And if you think about it, one of the most famous echinoderms, the starfish or the sea star, doesn't seem to have that. So it has what's called pentaradial symmetry. So what gives?

What's up with that? Yes, they are members of this group, Bilateria, because they have bilateral symmetry as larva. So, okay, so here is a young sea star with very obvious, you know, single plane down the middle bilateral symmetry.

It is as an adult that they develop into. this penta-radial symmetry. So don't have to redo this phylogenetic tree. We're off on a technicality and it makes sense. Some members have bilateral symmetry as larvae, but develop penta-radial symmetry as adults.

So we've covered all our bases there in case there was any confusion. So let's take a look at their anatomy. So again, we're using a C-star as a generic example here.

But again, there are other echinoderms. We're just trying to keep things simple here. One of the things we see in the C-star is with several of the organ systems, they exist in a central ring, whether it's the nervous system or whether it's the digestive system or whether it's... It's this water vascular system that we'll talk about in just a minute that exists in sort of a central ring and radiate out to each of the arms.

So this is kind of like those, you know, segmented worms that had a little bit of everything in each one of their segments. Well, the sea star has a little bit of everything in each one of its arms, which is why if an arm becomes detached, you know, ripped off in battle or something like that, it can grow into a new individual because it has a little bit of everything. It has everything it needs.

So, organ systems radiate out to the arms from a central ring. Another thing to point out about echinoderms is their skeleton. We've been talking skeleton in most of these groups.

They have an endoskeleton. So if you see a sea star like this in a beachside gift shop or whatever, that's the skeleton of a sea star. Some of them, you know, more gnarly looking than others, especially on, you know, a microscopic level.

This is a skeleton made of primarily of calcium carbonate. And again, this is an endoskeleton. It's the... inside as opposed to those exoskeletons that we saw with arthropods which were sort of outer armor. Okay now the water vascular system.

So this is something that is you know completely unique to this group and quite frankly kind of weird. So the way echinoderms move is through these tube feet. And the way these tube feet are powered is hydraulic pressure. So to go back to this anatomy here, here is, you know, the water comes in in this central part.

It radiates out through these arms. And with small muscles, they can control how much of this pressurized fluid goes into these tube feet and how much, you know. stays out of the tube feet in order to extend them and move them around and to crawl around.

Now that's not all. In addition to using this water vascular system for, you know, moving for locomotion, for grabbing prey and manipulating them. This water vascular system also functions as a circulatory system.

So this is why I wrote closed. It's not a traditional closed circular. circulatory system with true blood, like we see in other animals that have closed circulatory systems.

But really, it's unique. But it's probably more appropriate to call it closed than it would be to call it open if we're trying to keep things simple. So here's my summary of all that.

Phylum Echinodermata members have a unique water vascular system. This is formed from the phylum, so they're using this body cavity to do this. It uses hydraulic pressure to power movement of these tube feet. It's used for locomotion and prey manipulation, and also functions as their circulatory system.

Okay, well, that does it for echinoderms. Now there's just one group left, phylum chordata. And so it's actually at this point that we have to transition to the next chapter, which is entitled vertebrates. Now, It's called vertebrates, but we're actually not on vertebrates yet.

We actually have to talk about chordates before we can get to vertebrates. So it's kind of a weird way to transition the chapters, but it is what it is. So, OK, what is a chordate?

Well, chordates have. These five features, I've highlighted one of them here, but only four of them are drawn. There are five features that distinguish, that are unique to chordates.

One of these is something called the notochord. This is a flexible rod that supports the body that, you know, in some members can, you know, form a skeleton, act as a skeleton. But in the basic chordate, it's just a nerve chord. So there we go.

This is still clade deuterostomia, phylum chordata. Members have five features. And this is sort of an important parenthetical point. They have... all chordates have these five features at some point during their development.

We're going to see it is very possible, and we see this within our own bodies, for these features to be lost, but they're all seen at some point during development, even if they're not present in the adult. So, okay, feature number one, notochord, a flexible rod that supports the body. Okay, in addition to that, we have the dorsal hollow nerve chord. So, this is a Also dorsal here along the back.

This is a nerve cord and it relays information. This forms the spinal cord and the brain in humans, for example, but it doesn't have to be that sophisticated. Pharyngeal slits or pharyngeal pouches are located near the mouth.

And these are used to help in filter feeding. This is definitely one of those features that has been lost or certainly. reduced in function.

It is not used for filter feeding in humans. But, you know, if you look at embryology, if you look at human embryos, this is present at certain very, very early stages. Because, yeah, just to let you know, humans are going to be coordinates, of course, because we haven't come to ourselves yet. So pharyngeal slits, openings behind the mouth can be used to filter feed.

And finally, the fifth feature, which wasn't labeled in this original figure, but I sort of drew a picture around it here, something called the endostyle. This is a mucus-producing tissue that also aids in filter feeding, and it's another thing that humans don't have apparent. Oh, sorry. Turns out I can't count. This was only number four.

Number five is the post-anal tail, a tail that extends past the anus. So. This is another thing that humans have lost, but we have during our embryonic development, this post-anal tail, tail extending beyond the anus.

So we can also say if we want to finally finish this table here, that chordates are coelomates and we have a closed circulatory system. So that lets us finally finish out this table. And again, It seems like a phenomenal amount of information, but, you know, for most of these things, they're all bilateral except for a couple. They're all triploblasts except for a couple.

you know, the protostome, deuterostome is easy enough, and then it turns out to not be that much information about remembering which ones are acelamates, pseudocelamates, selamates, and the circulatory systems of each of these groups. So this does not have any new information. Everything on here I've mentioned throughout, you know, last chapter, and this one on, you know, these slides that I have text, but, you know, this is just a convenient way if you want to screenshot this or whatever, or draw this out yourself.

to just organize all of this information. So now that we know what it means to be a chordate, on to the vertebrates, right? I mean that's what the chapter is called, vertebrates.

Well actually we can't get there yet. As it turns out, all vertebrates are going to be chordates and you know have these chordate features, but there are actually two groups of animals that are chordates. They are members of this phylum chordata, but they are not vertebrates. They don't have a skull or a spine or things like that. we don't want to call these invertebrates because invertebrates typically refers to, you know, all of this other stuff, all the phyla that are not chordates.

But we can't call them vertebrates either. So these two weirdo groups that are chordates but not vertebrates are referred to as non-vertebrates. Sorry if that's confusing terminology, but I don't make this stuff up.

So what are these weird non-vertebrates? Well, one of these is subphylum, and yes, it's a subphylum because this is underneath phylum chordata, subphylum cephalocordata. Members are called lancelets because I guess they kind of look like a little lance, whatever. These look like fish, but if you examine them more closely, they're definitely not fish.

They don't have any... any bones they don't have a skull they don't really have a well-defined head you know they certainly don't have eyes or or teeth or any of that stuff they definitely have all the apparent chordate features they got the pharyngeal slits the post-anal tail they you know they have the dorsal nerve cord and notochord and the endostyle they got all this you know chordate stuff but You know, they are definitely not vertebrates. These are filter feeders that bury themselves in, you know, sand or rock and, you know, filter particles out of the water.

So not much to say about them. Subphylum cephalocordata. Lancelets, Filter Feeders, and these are one of those two non-vertebrates. The other group of non-vertebrates is Subphylum Urocordata. Members here are called Tunicates.

and man these things are weird looking so this includes bluebell tunicates and this looks like a heart uh at the bottom of the ocean uh this this sea squirt um these are really weird because this thing doesn't look like it has any of those chordate features, certainly not things like the dorsal nerve cord. It doesn't look like it has, you know, a mouth and an anus, this sort of tube-shaped body. Well, that is because it has lost these features. during its development. So if you look at one of these tunicates in its larval form, okay, you can see all this.

You can see the pharyngeal slits here. You can see the anus. You can see the notochord and the dorsal nerve cord. It's as an adult that it takes on a very different shape and loses a lot of these features, but has the body plan that it has as an adult. And again, is a filter feeder.

So the larvae have chordate features, most are lost in adulthood. They're filter feeders. Most of them are sessile, you know, attached to rocks or something in a filter feeding. But there are actually some really cool salps, is what they're called. Might be confused for a jellyfish, a sea jelly.

But this is a chain of colonial tunicates that, you know, exist within the ocean floating around. And being a filter feeder. But either way, some grow in long chain colonies, but at the end of the day, they're still filter feeders. So, okay, those two subphyla were what we call nonvertebrates.

Now we're on to actual vertebrates. This is a subphylam underneath phylum chordata, subphylam vertebrata, also known as craniata. And so, you know, It's one of those terms that's sort of embedded in our collective consciousness that these are vertebrates.

We should call them vertebrates. It's vertebrata. But as we're going to see, the cranium actually came first. So craniata might be a better name for this, but right now they're kind of used interchangeably.

Members of this subphylum are called vertebrates. And again, the first evolutionary innovation was the head and the skull. which protects the brain. We definitely don't see that in in tunicates or or lancelets here.

And vertebrates, this subphylum is going to include all further groups. So at this point, I want to introduce a new phylogenetic tree. I made this myself.

It does not include everything, but it includes a fair amount of stuff. There's a chordate ancestor here working up in a stepwise fashion. So let's start by talking about fish. Well, okay, where are fish? Well, there's...

bony fish but these are some lampreys these are also fish fish is a paraphyletic group fish the things that we call fish that is not a single clade it is not an ancestor in all of its descendants it's several clades that we sort of lump together we exclude all the other vertebrates to to create this group so fish is not a clade it's a paraphiletic group but you can't not have fish it's a it's a term that still exists uh even if it's even if it's not a clade so most fish are uh ectotherms so this is a new term at this point it's uh defined within the key terms, sometimes colloquially called cold-blooded. The formal definition of ectotherm is an animal incapable of maintaining a relatively constant internal body temperature. So they rely on their environment for their body temperature, and we'll see this again in other groups, but yeah, just introducing this because it's the first time we've seen this.

Okay, so the simplest of fishes is a group called hagfish. these are limbless uh kind of look like an eel but you know eels are going to be very different uh these are limbless scavengers and you know here's a picture that maybe shows this a little bit better um they'd have a skull uh but no vertebrae so again the skull evolved first so these are the uh most ancient living fish uh because they're at this you know primitive stage where they have a skull but not any vertebrae yet. These are sort of eel-like, just referring to their limblessness scavengers.

Okay, our next evolutionary innovation after the skull is the vertebral column, the spine. So we see this in the next group of fish called lampreys. Here's a cartoon of a lamprey.

Here's some other drawings of lampreys. Here are some terrifying photographs of lampreys. Actually, that's... a fish there's the lamprey uh attached to it um and yeah they do have a skull they do have vertebrae uh they don't have a jaw uh so they they have these teeth that you know they use to attach themselves to their hosts these are all either filter feeders or parasites so without a jaw they they can't really be hunters or carnivores but they can definitely be parasites and filter feeders so lampreys have a skull and a vertebral column.

And yeah, noting that these vertebrae, that's a replacement for the notochord. Again, the job of this is to protect that spinal cord, doing the bone here, doing a much better job of that than the notochord, sort of an extension or growth of that. And again, no jaw, we'll see that soon enough. Lampreys are parasites or filter feeders.

Okay, so they don't have a jaw. You can probably guess what the next major evolutionary innovation is. A jaw! And so the clade that we're in now is called Natostomata. And this is a clade that can be called jawed vertebrates.

So notice it's not jawed fish, it's jawed vertebrates. So the evolution of the jaw is something that happened in early fish, but it's something that's passed on from fish to all of their descendants, onto amphibians, mammals, reptiles, birds. So this clade of gnatostomata, jawed vertebrates, this includes everything to come. We are jawed vertebrates, obviously, with our jaw.

So they have a skull, a vertebral column, and a jaw. And again, this is a big deal. The jaw enables for additional modes of feeding. You can chew up food, you can hunt prey more effectively.

Yeah, this is big. There's a reason why virtually all vertebrates alive today have a jaw in one form or another. Okay, so our next group, again we're under this umbrella of jawed vertebrates, is a class called class Chondrichthyes. This includes sharks, rays, and skates. These are sometimes called cartilaginous fishes, because, I mean, you can't really tell by just looking at this skeleton, but it's made out of cartilage.

We have cartilage, you know, in our earlobes and in our nose. Instead of having a heavy bone skeleton, they have a more lightweight, flexible cartilage skeleton. So, chondrichthys, cartilaginous fishes.

sharks and rays. So they're called cartilaginous because they have a cartilaginous skeleton, not made out of bone. It's lightweight, but it's not as strong as bone. So there are going to be some upsides and some downsides to this, and there's going to be, there are some reasons for this. A lot of these need to move to not sink.

That means they don't have a good physiological solution to, you know, affect their buoyancy. So the way to not sink to the bottom is to keep moving. And in fact, a lot of these have to keep moving to keep breathing. These sharks called obligate ram ventilators. So they need to constantly be on the move.

And if you have a really heavy skeleton, that's burning a lot of energy if you have to constantly be moving to either breathe or to not sink. So that's the reason for the lightweight cartilaginous skeleton, because again, it's definitely not as strong as bone, but it cuts down on the amount of energy you have to spend to move around. And yeah, a lot of them definitely have to move around to avoid sinking or drowning, essentially, if they don't get new water on their gills. So the light skeleton reduces energy spent in movement. There are some features here that we don't want to discount.

Paired fins uh doesn't seem like a big deal but you know this is definitely an upgrade over these limbless lampreys and the the limbless hagfish uh so having you know paired fins one on either side of the body is is a is a big thing that we're going to see in pretty much all further groups as well most can drink these are marine and as we know most of these are carnivores so uh there are so this is a this is a class If we want to talk about the rest of fish, that's actually not one class. There are several different classes of what we collectively call bony fishes. So this is a, I'm not going to break things down to the class level, although the classes certainly exist. I'm going to lump together all the fish with bones into a clade called clade osteichthys. So these are called.

the bony fishes. And yep, they're named appropriately. They have a skeleton that's not made of cartilage, but is made out of bone. And again, it's the exact opposite of cartilage, which was lightweight, but weaker. The bone skeleton is heavier, but stronger.

So this is accompanied by a couple of evolutionary innovations that help them, you know, not sink. The weight of this heavy bone skeleton is offset by air. in a structure called a swim bladder. Chondrichthys do not have this, only bony fishes have this.

The swim bladder is an organ that is attached to the circulatory system. gases can be put into the swim bladder or taken out of the swim bladder allowing the fish to to regulate its its buoyancy and so it can stay at a certain level in the water and not sink even though it has a heavy bone skeleton so this again this sort of goes together with the bone skeleton the swim bladder allowing it to maintain its desired buoyancy another feature that kind of goes with this heavy skeleton is a structure structure called the oparculum or gill cover. So one of the things that we saw in sharks were, you know, their fin or their gills, you can't see them very well here, their gills are just sort of exposed to the surrounding water. Many of these, like this shark, have to keep moving to expose their gills to new water. Of course, that takes a lot of energy to keep moving.

If you have a heavy bone skeleton, you want to avoid having to move constantly. The operculum or the gill cover is a cartilaginous flap that not only protects the gills, but has muscles attached to it so it can flap back and forth, circulating water over the gills, allowing this fish to breathe, to have new water exposed to its gills without having to swim around constantly. So this...

This is also sort of related to the heavy bone skeleton offsetting the weight of that by not having to move all the time. So members of Cladosteichthys have an operculum, or a gill cover, that protects the gills and helps pass water through the gills. Now... There are, sorry, I think I said a minute ago I wasn't going to get into the classes.

I lied. I'm not getting into all of the classes because several of them are extinct. There are two extant classes, meaning not extinct, that are members. of this clade of bony fishes. The biggest one by far is class Actinoptergii.

It's quite a mouthful, Actinoptergii. These are called, yeah, these include... virtually all bony fish that you can possibly try to think of.

It's going to be easier to remember the like two bony fish that exist today that are not members of this class. Members of class Actinoptergii are called ray-finned fishes. Again, this is within clade osteopthes class Actinoptergii ray-finned fishes.

This includes almost all bony fish alive today, and they're called... ray-finned because their fins are webs of skin with thin spines. So here's a cartoon of this. Yep, there's one of the fins.

And yeah, there's some bone here, but most of the actual appendage is just this flat, thin ray. It's not a very robust appendage. It works just fine for them.

They're extremely successful throughout the planet, but yeah, their fins are pretty simple. In contrast, the other class of living bony fishes is class Sarcopturgii, and this only has a couple of members, a few species of lungfish and the coelacanth. These are known as lobe-finned fishes, very few living members.

And obviously the difference here is in their fins. Instead of being thin rays, these lobe-finned fishes have much more robust fins filled with bones filled with their own muscles the fins and rayfin fishes are attached to the shoulder basically and they use shoulder muscles to move back and forth here there are muscles within the the appendage within the the fin itself so this is worth pointing out and this is worth uh you know bringing up these muscular bony fins possessed by class sarc coptergii because what we're going to see is these are the precursor to the weight-bearing limbs of all further vertebrates. So these are the ancestors to what would become amphibians and then mammals and then reptiles and then birds. And again, you can track these synapomorphies to go back to that term from the very first lecture in the quarter.

The bones in these... these lobe-finned fishes correspond to bones of living land vertebrates and other extinct links between them and the land vertebrates that exist today. Again, evolution is all about taking something that already exists and modifying it. And so if you have a limb that's filled with muscles and bones that can be modified to form a limb that can bear weight on land and that is what the evidence points to so the fins of these sarcoptergii evolved into the limbs of all further vertebrates and we'll talk about all further vertebrates uh in the next lecture so this is typically my cut off at the end of fishes before we get into the rest of vertebrates this is the end of recorded lecture three five This is also the cutoff for exam number three. So we'll get into amphibians, birds, and mammals, and all that fun stuff for the fourth exam.

This is the end of exam three stuff.

Transcript for:Invertebrates and Chordates Overview

Transcript for:
Invertebrates and Chordates Overview