Hello BISC-132, this is the beginning of Recorded Lecture 3-4, still in invertebrates, and picking up where we left off last time, we started on mollusks and started talking about some of the classes within phylum mollusca. We just have a couple of left before we can move on to the next phylum. So up next we have class Cephalopoda.
This includes nautiluses, cuttlefish, squid, and octopi. Something should be... associate all of these with class cephalopoda octopuses, squids, cuttlefish, and nautiluses.
Just looking at their bodies, these are perhaps the biggest departure so far from kind of the typical mollusca body plan. You know, the foot anchoring to the ground is absent, and the mantle and the shell is absent, or at least it seems to be absent. Really, all this stuff is here. it's just been modified highly.
So let's start with the shell. So some of these, like the nautilus, have a shell that's very obvious. In other members it's less obvious.
So squid, for example, have this internal shell called a squid pen, the function of which is not well understood, but I mean that's what the structure looks like. And in cuttlefish This is a structure, this internal, called a cuddle bone, although it's not real bone like an endoskeleton, but this part of the mantle internal is used to regulate buoyancy. And I thought this was fun when I was searching for images for this.
And I guess it's used as a dietary supplement for birds. If you have a pet bird, you can find cuddle bone in the pet store or whatever. But yeah, so members of class cephalopoda may have a shell.
and in some species it is completely internal. And the foot is something else that's been modified greatly. Instead of being something that, you know, anchors the animal to the ground, the foot is modified to form several arms, you know, the exact number depends on the species, several arms or tentacles that can be used to to grab stuff. So these structures are still there, the mantle and the foot, they just look really different.
So foot is modified to form several arms slash tentacles, which may or may not have suckers to grab things. The reason why I said most mollusks have an open circulatory system is because encephalopods are the exception to this. They have a closed circulatory system with real blood and blood vessels and everything you associate with a closed circulatory system. Now, The way they move is also a little bit different. Like I said, the feet here are not used to crawl along the surface in most cases, like the the foot of a gastropod or a chiton, for example.
The way cephalopods move is through jet propulsion, which sounds cooler than it actually is, but what it means is they take water into this cavity, expel it out, and that propels them in the opposite direction. Here's another figure showing kind of the same thing in slightly lower quality. Direction of water out of the siphon, so shooting water out this way in the direction of the arms and tentacles, and that propels them, you know, backwards in the opposite direction.
Technically, that's jet propulsion, although it's not, you know, burning jet fuel or anything like that. So they move using jet propulsion. Water is sucked into the mantle cavity and forced out to propel the animal.
what we would call backwards. Okay, so one last class here in phylum Mollusca, and that is class Scaphopoda. This means boat foot.
We're gonna see poda a lot in this in the next chapter. Poda always means foot. And yeah, I guess that kind of looks like a boat, a canoe or something like that.
Here's someone holding this up just to give you a sense of the scale of this thing. And yeah, it's got a foot that anchors it into the soil, similar to that of some of the bivalves we saw. There's the mantle, there's the shell.
Unlike bivalves, which have two shells coming together, the tusk shells here in Class Scafopoda are open at both ends. So they have a very different sort of conical shell. So not much to say. Class Scafopoda.
Tusk shells or tooth shells, a conical shell, it's open at both ends. Okay, so that finally brings us to the end of phylum mollusca. We're now moving on to phylum annelida.
So this is still in protostomia, and this is still in Lophotrochozoa phylum annelida. And members of this phylum include a couple of what might be familiar species, earthworms, leeches, but others as well. So these annelid worms, as they're sometimes called, or segmented worms. have some distinguishing characteristics. So the phylum annelida, segmented worms.
I mean, obviously we're familiar with like the earthworms, the terrestrial members, but there are aquatic members as well, like this one, and we'll see some others in just a minute. These are coelomates. So if you'll remember, these were the example of the coelomate body plants.
So here's the body cavity within the mesoderm. And they use... use their sealant in a very interesting way. So, their body plan is segmented. I mean, hence the name segmented worms.
And as you can see here, there's a dorsal vessel, blood vessel, ventral vessel, blood vessels. Okay, so if we see blood vessels in the body, that tells us it's got a closed circulatory system. But what we also see is, you know, outside of these blood vessels, this fluid here in the coelom cavity.
Now, we're looking at... kind of a strange cross section here so it's maybe kind of hard to see this. Yeah there's the coelom labeled right here. Each one of these segments has its own coelom fluid that is separated by a partition from the segment next to it and then from the segment next to it and then so on. So the coelom within any given part here, any given segment here, kind of acts like a circulatory system.
It allows, you know, dissolved things to flow around, to circulate within this specific segment. And that is... you know, that is redundant with what I just said, that they also have a closed circulatory system.
So they really kind of have two, that the closed circulatory system moves blood laterally throughout the body of the worm. And then within each segment, the fluid in that selum circulates stuff within that segment. I hope that makes sense. Here's my way of trying to put that into words.
So their selum meets, the selum is divided into segments by partitions called the septa fluid in the selum fulfilled. the function of a circulatory system, but they also have a closed circulatory system. So we can fill this table out now for Analyds, Seelamates, closed circulatory system. Now there's something else to note on here.
There's actually a lot to note, but I'm obviously skimming over some stuff. We're not getting into too much detail. But I do want to point out these setae, these bristles. So these help the worms crawl along.
They help attach to surfaces so they can flex their muscles longitudinally and crawl through the dirt. So these bristles called setae on the ventral surface, that's their stomach basically, aid in locomotion. But that's in a terrestrial worm, like an earthworm. these setae are part of what's called parapodia when we look at aquatic worms uh so you know going back to to this one yeah there are the parapodia here uh and they're much larger uh compared to the setae of you know terrestrial members of this phylum and they fulfill a couple of functions uh they you know help them swim uh but they also help with respiration so gas exchange can be performed through through these bristles. So setae are parapodia in aquatic worms.
Respiration is through the skin or through these parapodia if we're talking about aquatic worms. Now we will get into the class level with these annelid worms, but there are only two classes that I want to note. One of these is class Polychaeta.
This includes the aquatic member we've been looking at, the bearded fireworm, as well as some other weird ones, very fun Christmas tree worms, the bobbit worm, all this stuff is interesting. You don't need to memorize these names. This is just, you know, for your info.
All you should know is that class Polychaeta is what we call bristle worms, and these are aquatic, mostly in saltwater, mostly marine. If we want to start talking about the terrestrial members, we have to move on to class Cletelata. This includes earthworms and leeches.
this class is named after a structure that most members have called a clitella. You can see it on the earthworm here. Let's zoom in a little bit more. There we can see a little bit better in this figure.
There's the clitellum. So in the rest of the body the segments are pretty apparent, and there's the setae again, but within this clitellum which is located about a third of the way down from the mouth, it's smoother. It kind of looks like, you know, this is smaller, but you can see it here as well.
sort of like a band-aid or something wrapped around the worm. It's thicker but it's smoother. The function of this is defined in the key terms.
The clitellum is a specialized band of fused segments which aids in reproduction. So basically when these worms mate with one another they'll exchange eggs and sperm, they're hermaphroditic, and they'll use this structure to harbor those fertilized eggs and sort of serve as cocoon for those young worms as they grow and ready to, you know, come out of here. And that's the structure for which this class is named. All right, that's it for annelid worms, and that's it for this Lophotrochozoa. We went through all of these, so we're going to turn our attention next to this group called Echdysozoa.
So this is a superphylum, Echdysozoa. All members have, I say all members, there are only going to be two major groups within here that we're going to talk about, but all members have a protective cuticle exoskeleton. So this is a new way of doing things.
We've seen hydrostatic skeletons, we've seen, you know, some internal skeletons in the sponge, for example, but this is, you know, a skeleton that's on the outside and it's going to be very effective, especially in arthropods, but there's a downside to this. Because your skeleton is on the outside, it's protecting you, but it's also encasing you. It's trapping you.
Members of this superphylum have to molt in order to grow. Shedding the old exoskeleton is called ectasis, more commonly known as molting. But the technical term for this is ectasis. That's where the superphylum gets its name, ectisozoa. So here's an arthropod, a cicada.
going through this process of molting. But we're actually kind of skipping ahead here because we're not going to talk about arthropods first. We're first going to talk about nematoda. So again, just reset ourselves here.
Clade protostomia, super phylum ectizoa, phylum nematoda. These are called roundworms. They're not much to look at, to be honest. They're microscopic, or sometimes they can be seen with the naked eye, but they're very, very, very small. And yeah, they kind of look like boring worms.
They are pseudocelomates. You may remember them as the poster children. There's nematode for the pseudocelomate body plant, so that's interesting. They're using this pseudocelum as a hydrostatic skeleton.
I told you we would see that many times. Round worms, nematoda, most are microscopic or very small. They're pseudocelomates.
They use the pseudocelum for their hydrostatic skeleton. And honestly, there's not much else interesting about them. Just looking at their overall anatomy like this.
I mean, there's the pseudocel, this cavity filled with pressurized fluid. Not much else unique about them. they are so small, because they are microscopic or very small, they don't need a circulatory system.
So that allows us to finish filling out this table. Nematoda, of course, still triple blast bilateral protostomes. There are pseudocelomates and NA for circulatory system. So What can I say about Pseudocelomates, or I'm sorry, about these nematode roundworms? Well, some of the members are free living in the soil.
You scoop up a small amount of soil, you're going to have some of these worms in that soil. around eating bacteria. Several of these are prominent pathogens.
Heartworm in cats and dogs is caused by anematodes or pinworms, so is trichinosis. Cook your pork chops all the way. But the most interesting of these, if we want to go a little bit further, is actually this one, in my opinion, the one that just crawls around eating bacteria.
The reason why I think this is more interesting than any of these parasites, any of these pathogens, is because, and we've used this term before, it's a model organism. This specific species, and this is a mouthful, Canorhabditis elegans, usually just abbreviated as C. elegans.
C. elegans is a model organism for genetics research. So it's been a while since I used this term last, back in, I think, chapter 17 or something.
So it's defined in the key terms for this chapter as well. A model organism is... a species that researchers study and use as a model to understand the biological processes in other species represented by the model organism. So as far removed as these worms seem to be from humans, they do a lot of the same stuff that humans do. Here is a worm that has been genetically modified to express this glowing green protein only in its neurons.
So the whole worm is see-through, so you can, you know, alter its genetics like this, and it's very easy to see certain... parts of it and this is used to study whatever you want to. So I worked on the same floor as a lab that did neuron pathfinding back when I was in grad school and so they would label the neuron neurons green, and they would mess with it genetically, and then try to see how the neurons are supposed to find each other and make these connections. Again, these worms are way simpler than a human, but neuron pathfinding, for example, is something that worms do and humans do, and we don't understand it completely. And it's way easier to try to understand this fundamental aspect of biology in something like a worm that you can just grow on a petri dish and feed it E.
coli than... than you could in anything more complicated than this worm. So they make great model organisms.
If you do research in genetics, chances are you're probably going to be working with fruit flies, zebrafish, or sea elegans if you're working with any model organism at all. So these are pretty big. They're easy to care for and to propagate. Again, they're hermaphroditic. And there is a robust system for genetic alteration that exists.
That just means they've been worked over for a while. so many years and decades that It is now very easy to mess with their genetics. And that's what we do to understand them better, to understand us better. We mess with their genetics. So that's what makes them such great model organisms.
Okay, so that's all there is about nematoda. Let's move on to the other member of Echidizozoa arthropods, Phylum arthropoda. So clade protostomia, superphylum Echidizoza, Phylum arthropoda.
And this is... is a big one. Okay, this isn't a big one. This is the big one.
Do not memorize these numbers. But this is just, you know, an interesting overview of all these phyla that we've talked about and we'll talk about and the approximate number of species that are members of that phylum. And, you know, most of these are a few thousand, you know, I said mollusks were big.
That's about, you know, 100,000. But most of these others, you know, 20, 25, something like that. Arthropoda, 1.1 million.
That's almost 10 times the number of known species as the next leading phylum. So this has a ton of members and there's a lot of diversity here. So Arthropoda is going to include all of this stuff. It's going to include spiders and scorpions and lobsters and mosquitoes and extinct stuff like trilobites. And yeah, this is only just scratching the surface, obviously.
This is a gigantic... phylum. So what are their characteristics?
Well, members of Phylum marthropoda are coelomates. And we saw this with mollusks. Their coelom doesn't do much. Their coelom is reduced in function. It only surrounds it.
reproductive system. So they have this as part of their development, but they're not doing anything important with it. And they have an open circulatory system.
Of course, here's the, you know, the insect grasshopper that was the example of an open circulatory system. lets us fill out the table here, arthropods, coelomates with an open circulatory system. So we have all these different species, the greatest number of species, greater than any other phylum. And so a very easy question to have is why this phylum? What makes Arthropoda so big?
Why are members of this phylum so successful? Well, there are several answers to that question. They have to do with their morphology.
Members of phylum Arthropoda have what we call jointed appendages. So let's take a look at this B just as a, you know. generic example of an arthropod. And yeah, what I mean by jointed appendages is that, you know, here's a leg, for example, and it's not, you know, one long stick, you know, one tentacle or something like that. There are points of articulation along the lip.
Now, this doesn't seem like a big deal, but this is huge. Think about all the invertebrates that we've talked about so far. This is the first time we have an...
animal that can you know crawl around on on actual legs i mean we've seen terrestrial worms and we've seen you know a lot of stuff that lives in the water uh but these these limbs can really bear the weight of a much larger animal in in a way that's that's much more effective than that of the worm type body we've seen a lot of worms so far so that that alone uh just as legs have made them very successful in terrestrial environments. But that's not all. I said jointed appendages. That doesn't just mean a leg.
You know, we talked about the hawk's genes. And, you know, so a lot of the genes involved in building a leg are very similar to the genes involved in building an antenna. So antenna is just a modified leg.
And so are wings. So here's the very first time we've seen a flying animal. So this opens up a top. ton of new ecological niches and ways to live and lifestyles.
And so just this one simple thing of having jointed appendages means you can do all of this stuff. They can bury your weight in the form of legs. They can sense the environment in the form of antennae. They can manipulate food, which opens up new modes of feeding in the form of mandibles or maxillae, as the case may be.
And they allow for flight. So yeah, this is huge. This is why they are so widespread.
spread and so successful. Another feature of their morphology is what we'll call a segmented body. I mean, we've seen segmented worms and stuff before, but what I mean here is that the body is organized into functional units called tagmata.
In the bee... for example, there is a head, a thorax, and an abdomen. That's three, uh, tagmata, uh, and yeah, we'll see either three or two in most arthropods, and yeah, it's just a convenient way to organize a body.
Of course they have an exoskeleton because they're members of Ectisosoa, but they have a chitinized exoskeleton, so it's even tougher than that of the roundworms. We didn't really talk much about their exoskeleton. This makes it exceptionally strong, but also flexible.
But again, there is a downside to this. They need to molt to grow, and they're very vulnerable during the molt and right after the molt. but it's some downsides and some upsides here.
This is part of their success because this is a great skeleton for their size. Okay, so of course, if this is the largest phylum, we have to talk about some of the classes that are within this, but actually this is such a large phylum. If we want to get more specific, we're actually not going to go to the class level.
We're going to go to the sub. phylum leveled that's that's how many different groups are within this where we need this extra level of taxonomy this extra level of organization so let's start with uh not class but sub phylum chelicerata this is going to include spiders ticks scorpions and There's usually an oddball in most of these subphylum horseshoe crabs. So you should associate these with this subphylum, spiders, scorpions, ticks, and horseshoe crabs. They're named after these Chelicerae, these mal... parts.
Here's a spider here. You've got your eight legs. You've got pedipalps. These are sensory organs, not weight-bearing appendages. And yep, they're the danger mustache, the chelicerae that can have fangs that produce venom.
That's the structure for which this group is named after. And again, they don't have antennae like a lot of other arthropods, like our sort of generic bees, so that's something that distinguishes them. Instead, they use these pedipalp appendages as a sensory organ. And yep, there they are, the pedipalps on this spider. Another unique thing about members of this subphylum has to do with their respiration.
So here's a cross section of a generic bee. generic spider. In spiders in specific, they use something unique to them called book lungs for respiration. So this is... kind of look like pages in a book you know these stacks this is stacks of hemo seal that you know cavity that contains the hemo lymph fluid part of their open circulatory system but because it's stacked like this because it's got all these rows it's got all these extensions here that increases surface area.
We've seen this a lot, whether it was roots or mycelium or whatever. It's that same strategy. Having a bunch of extensions here gives more surface area to do gas exchange, not pumping air in and out like vertebrates are going to do when we have lungs, but allowing for passive gas exchange. But by having these stacks here, it increases the effectiveness of that.
So again, this is unique to spiders. Many use book lungs for respiration, stacked pages of hemocyle with air pockets in between. Again, that helps them breathe, that helps them do gas exchange.
Okay, next subphylum is myriapoda. I'm just trying to put this together. I told you we'd see a lot of poda. Myria, think of the word myriad. Myriad means many or lots of.
Poda means foot. So if you put those two together, okay, this seems obvious. This is centipedes and millipedes. millipedes members of this sub phylum and despite the name you know centa means 100 like a century and milla means a thousand like a millennium centipedes do not have 100 legs and millipedes do not have 1,000 legs but millipedes do usually have more legs than centipedes that's just fun trivia you should know that this is kind of obvious members of myriapoda have numerous repeating body segments so Again, this is what I mean by the success of this overall phylum. You have the idea of having these tagmata and being able to just duplicate these over and over and over again without having to reinvent stuff allows for different body plans.
So just taking a structure that's highly modifiable and then modifying it and coming up with new effective body plans. Okay, next we've got subphylum. crustacea. So this is going to include a lot of things that we like to eat, you know, shrimp, crawfish, lobsters, you know, several other things that we don't typically eat. Other crustaceans, things like barnacles.
pill bugs also known as roly-polies here lots of krill are members of subphylum crustacea as well so you should know these most crustaceans are aquatic crabs shrimp lobsters and krill and you should know some of them are terrestrial pill bugs being sort of an oddity here i think most people would look at this and you know assume that it's maybe a really short uh millipede or something like that but if you look at its anatomy more closely it's a terrestrial crustacean Most have two tagmata. You can see this best probably in a lobster, this cephalothorax and then the abdomen as opposed to the three that we saw in the bee. So most have two tagmata, cephalothorax and abdomen.
And I told you the exoskeleton in arthropods is hardened with chitin. A lot of crustaceans take this even a step further. If you've ever tried to crack open a lobster to eat withdrawn butter or something like that, it's even harder.
than the exoskeleton of like a spider or a grasshopper or something like that. They harden, or many of them harden their exoskeleton with calcium carbonate to give it just an extra level of toughness. And that's something we don't see in other arthropods.
Okay, we're not done. We've got more subphyla to talk about in arthropoda, but this is typically where I run out of time in the in-person lecture. Sorry for another kind of, you know.
know mid phylum cut off but it's just the way it is uh we will pick up and finish and you know continue moving along uh with things uh in the next recorded lecture but this is the end of 3-4