Good morning, good afternoon, good evening, hello. Today we are going to continue talking about gastropods and we're going to begin to talk about cephalopods. These groups are going to overlap slightly because they are kind of amazing. There's just a whole whack of things to talk about with regards to specific adaptations that we see characterizing the class and... different larger character states that characterize the mollusks that might have been lost along the way.
So we started talking about gastropods last time together. We're going to keep going today and we've talked about the radula. We talked about different groups of mollusks, the aplocophrines, the monoplacophrines, and the rediscovery of the monoplacophrines and the role of remotely operated vehicles in that rediscovery. We started talking about gastropods and I give you the kind of tongue-in-cheek recipe of how to make snails and the importance of coiling and torsion and gut flexure.
Today we're going to keep talking about gastropods. We're going to talk about some specific examples, some deep sea thermal vent gastropods, the scaly foot gastropods that's pretty metal, like it uses metal in its shell, and then different adaptations of the shell for reflection, which is kind of amazing because it's not a thing that it has really no head as it's doing it. So we'll unpack that. We'll talk about feeding, about different adaptations for feeding departures from the ancestral state of a browsing herbivore to carnivory and the evolution of a symbiotic relationship with this kind of marvelous Elysia.
We'll talk about the foot. We'll talk about mucus and reproduction. And then we'll kind of move into our intro time with the cephalopods, and we'll talk about the synapomorphs for the cephalopods. So as we're doing that, that's all kind of sitting under the large umbrella of these three critical verbs of praising, synthesizing, and interpreting how the environment has affected the evolution of shells, of movement, of feeding lifestyle, and with gastropods and with cephalopods.
So with that out of the way, let's begin. This is the first example. This is a hot vent gastropod that has iron sulfide in its dermal sclerites. So it has a shell, but it also has sclerites.
Remember, sclerites were something that characterized, or the absence of shell in these sclerites characterized the aplacophrines. So this is a gastropod, deep sea, thermal vent gastropod. that we only learned about at the turn of the century, the turn of the last century, 1999-2000.
And using iron sulfide, using iron as a skeletal material, had otherwise not been known in metazoans before the discovery of this particular gorgeous creature, which we call the protection mechanisms of the iron plates for the deep-sea hydrothermal vent gastropod. This is the scaly-foot gastropod, Chrysomelon squamiferum. So this is known at the time from only a single thermal vent in the southwest Indian Ocean or in the deep thermal areas, the kind of line that run up in the Indian Ocean as a spine just to the east of Madagascar. And we now know that they exist at other thermal vents in and along the same area, but that water, that kind of basin, that ocean is where they seem to be restricted to. They fall along...
A story, an unpacking, a story that we're continuing to unpack of just so many things being discovered, particularly as we expose those deep thermal vents to new desires to mine rare earth elements from them. Just a real huge component of diversity that we really don't know anything about. So this particular case is one of the...
Kind of the exemplar one. So we discovered in 1999, and this is kind of, as we've talked about before, another example of the animal incorporating materials from its external environment into its construction capacity, whether that was the radula with the limpid in the last time together, or in this case, sulfides and metals from these belching black smokers, these thermal hydrothermal vent materials into the construction of its shell. and these kind of sclerites that line this part of its foot.
And so that reinforces the idea that fortifying these biominerals really reflects, like if it's there, and if the mollusk is there, they're going to incorporate it. The availability and time. So availability and time equals the mollusk incorporating that material into their construction processes. One of the cool things about this group as we over the past kind of 25 years that we've known of their existence, we continue to discover more and more things. And one of them is that just like so many other organisms, like when we talked about the alvanella, the pompeii worm, other characteristic gorgeous fauna from the thermal vent environment.
These ones rely on bacterial endosymbionts to produce for their nutrition and for their energy. Now, they've been, since their discovery, a real hot topic. There's my jazz hands and my dad joke about in the biomaterials front, because there is a lot, so they're incorporating this metal.
That's kind of interesting right off the bat. But then are there elements of this? their construction that allow them to live quite close to these incredibly hot temperatures. And it seems that there is. So let's unpack some of these images here.
We've got in this first images of the animal retracted in the shell and the scales and the shell are rusty. And so that's the iron in its body, but it's because of how it was stored. But it gives us this kind of very, looks like a sigil from like Game of Thrones or something. Then we've dissected off. in this preserved one.
The shell and you're looking at the head and the scales are kind of back to a normal color. And then we've got a longitudinal section of the scales so with those sclerites viewed with light microscopy and you can see this white text here the sulfur that so that's showing you kind of where it's sitting and then there's a protein around it. And we've got the sulfide layers and the protein layers in the scale that are incorporated to protect the foot.
Now, if we switch kind of from the ventral to the dorsal, we look at the shell. One of the things that's amazing here, and that from a biomaterial or a bioengineering perspective, is that we see real changes in how these characteristic... parts of the shell are laid down.
The ratio at which they're laid down is really quite strange or different from other animals. Now, take your mind back to the very first, like to Valentine's Day, to the very first time that we had with the mollusks. Because we talked about the mantle and the mantle secreting the shell and the different kind of characteristic layers of the shell. And there was a nacreous layer and there was a proteinaceous layer and there was a prismatic layer.
Okay? Remember all that? If you don't, pause, go back and look at it. Now... Now, one of the things that was uncommon or is now known to be uncommon about these deep hydrothermal vent snails is that the periostracum is much thicker here.
That the organic layer, so that there is iron sulfide in these outer layers, but then there's a very thick organic layer, much thicker than you would see in terrestrial or freshwater snails or marine snails, but not in these hot environments. And that seems to be a real... something for bioengineers to follow are those that are going to use, engineers that are going to use biomimetic solutions to provide these guidelines for the development of thermal barriers so that we can work and live in these, or work and maybe derive elements from these environments as well, which sets up an interesting juxtaposition. The vulnerability of the diversity at these thermal vents, as we learn about the diversity, we might...
might actually be learning about how to put our equipment there and have it survive, which might further jeopardize the diversity that has taught us how to be there like these snails have. So the hydrothermal vents where they're found are targeted for these deep sea mining of the mass of sulfide and other deposits. And the exploratory licenses have been issued for the area that includes the entirety of the known distribution.
of this particular species. And while we do know about this species, we know so little about the remainder of life that lives there, the highly specialized, highly isolated life that lives there. And if you stick with us in 3700 next year, you'll have an opportunity to dig into some of that diversity with a specific research project later on.
Let's talk about the shell a little bit more specifically. We've got a very kind of esoteric line drawing there that this is a very interesting one. This is not a cone that's shooting up, that's not what the arrow means, but the arrows there are showing you the inner lip and the outer lip. Remember we talked the other day about the fact that if they're growing, that one of them is growing faster.
So in this case, the outer lip is growing faster than the inner. That's how this whorl or this twist is going to be formed. And, and some of you already know this, I remember from the chat the other day, there are left-handed and right-handed snail shells.
That, so unlike that kind of physics, the, like the electrons flowing if you're blah blah blah, so this, this to me, this rule works kind of with the opposite hand. So most snails are right-handed, and that's this diagram at the top, and I show that to myself by sticking up my thumb towards me. That's the apex, that's the shell apex, and then my fingers are pointing towards me, that's the opening. And that is, although I'm using my left hand, that is a right-handed shell. That's most shells, that's most taxa.
If I use my right hand to show the same thing, apex of the shell, fingers pointing towards me, that's a left-handed shell. So the aperture, it's in relation, the aperture in relation to this, what is called in these diagrams, the axis of rotation or the columnula. So when it's... It's the aperture relative to the calendula when facing you, the observer. So in this case...
your fingertips pointing back at you. Most gastropods are right-handed. A few are left-handed. Some have both. And some of you have heard about this because of the famous British snail, because of course it would be British.
This Jeremy, who is a mutant snail of a species that is predominantly right-handed. And Jeremy was left-handed and there was a long search to find a mate for Jeremy. And this is one of the stages.
You can go read this Wired article about Jeremy using that cue. QR code there later on, because I think it's an up and down search. Now, I mentioned or I asked if you'd remember this mantle view.
This is it. So we've got the periostracum, the prismatic layer, and the nacris layer, all of this being laid down by the mantle. And you can see on the bottom right-hand side of the screen, in this case, the characteristic kind of three-lobed mantle, that the outer lobe that's secreting the shell, the middle lobe, and that is more sensory, can actually literally...
have eyes in it. Park that like kind of what? For when we talk about the bivalves with the scallops later on. Yeah, eyes just appearing everywhere.
Eyes in the shell, eyes in the mantle. It's like eyes in your elbow. Everywhere eyes. Crazy mollusks. And then the inner lobe, which is more muscular.
Now, limpets. Remember, we talked about limpets having the hardest teeth. They were in the news again.
2015 was a big year for limpets. And this was because of this. This gorgeously titled article about a highly conspicuous mineralized composite phototonic architecture in the translucent shell of the blue rayed limpet. So, basically what we have are this mineralized, so the blue rayed limpet, as you can see here, it's no secret as to why it was called the blue rayed limpet.
Let's actually take a look at the video and we'll kind of move it along. it along and you can see it as they hold it because it's science they've got some forceps so they're moving it back and forth and what you're seeing are these rays that appear and disappear relative to the observer dependent on the light that they're reflecting so what we've got if they take again with the scms the scanning electron micrographs of the cross sections of the shell and we take we blow up this section of the limpet shell. And what we see from the periostracum through the ostracum into the hypostracum from the outside of the shell to the inside of the shell is through, there is an irregular laminalis layer, and then we've got this photonic multilayer with colloidal particles, and that is periodically layered with a bit of a zigzag architecture that's underneath the photonic multilayer.
And this secondary cross lamellar layer has light-absorbing particles that then provide the contrast for the blue color. Now, That's great. And I wouldn't probably ever ask you as a learning outcome to remember the physics as to why, unless that's something that interests you, go ahead and seize it and seize the day and run with it.
I'm more interested in you thinking about why. The limpet doesn't have eyes. Why does it have this super attractive, let's go back and take a look at it, and say, why is there this very showy display? The near-translucent shell with the blue rays on it, why is there this very showy display?
for an organism that has no eyes. Now, I'm going to put up this little timer again to remind me just to pause for a second, but what I'm going to encourage you is take this low-risk time and think for a second and come up with some ideas as to why. Why might the organism that has no eyes, no head, have Blu-rays, such gorgeous, visible Blu-rays? Why would it invest in that?
All right, so I'm interested in your ideas. What I'm going to show you is what the hypotheses, the ideas of the authors of this paper. So what you're looking at here, Western Europe, and the blue indicates the range of the blue-rayed limpet.
These dots, so that's shown in blue here, there's the limpet. The dots represent the distribution of these other... nudibranchs, different kind of mollusk. So the blue rayed limbate, primitive eye pit, so photoreceptivity but no eyes per se.
So they could not recognize the blue stripes of any conic pacifics. What they think, what the researchers hypothesize is the blue rays, if you take a look at the distribution of all these other nudibranchs that are distasteful, that retain often cnidocytes that they have consumed from cnidarians, and are toxic, therefore, that that blue color in these mollusks, shell-less mollusks here, is a real signature of toxicity to any potential predators. And the overlap, the near overlap, in the blue-rayed limpets distribution with all of these other truthfully toxin-advertising taxa is a way to...
to hide within that signal. So for these tags, the toxicity is real. For the blue rayed limpet, there is no toxicity. And the hypothesis is that they may have these blue rays because it has provided some protection.
to the limpet from predators that avoid it because they have learned to avoid that blue color because it's associated with the toxicity of these other mollusks. Kind of cool. What they're eating, who they're eating, gastropods all over the place. So ancestrally, certainly we've talked about radulas scraping plants and algae, right?
But carnivores as well. Some of you know about cone snails. Cone snails are kind of amazing things where they've lost that odontophore and the radula is adapted so that it can, and the siphon changes so that it essentially becomes a really terrifying predator on fish.
Thank you. Others are suspension feeders and raptivorous animals, literally flying in the ocean and often suspending a mucus net that they're kind of collecting particles and then engulfing them. Or nudibranchs, like we talked about, these are nudibranchs up here from Papua New Guinea, I believe, that are grazing on cnidarians and saving and using those undischarged nomadicists. co-opting those from a different phylum to use them for themselves.
Then there's sea butterflies that prey on unshelled other flying gastropods. So the sea, the shell-bearing ones are the ones that are suspension feeders that have a mucus net kind of out in the world, in the water, and are harvesting particles off of that. And then these guys fly in and eat the other ones.
Some of them, this is a gorgeous one. This is an open ocean nudibranch that looks like a fish, swims like a fish, eats like a jellyfish. How much does it look like a fish?
Well, there's this image you can see. It's kind of very laterally flattened. It looks quite a bit like a fish. bit like a fish we can do better here's a video of it moving through the water literally with a fish like motion and there's one of it that's been collected and is in a tank kind of amazing Now this is harder to see but zoom in there and what you'll see this is the shell-less snail, Terobrancha coronata.
You see that trunk? So there's a hole this is the environment, the number of feeding strategies that gastropods have adapted has diverged greatly from the ancestral state of rasping on algae. It also now includes deposit feeders in scales.
scavengers. So this is a snail. This is a bit of a decaying Cnidarian on the shore.
All of these other animals are snails that are coming up through the sand to come in and feed on detritus, dead plants, animal flesh, all sorts of things. really have quite high population densities, even when you as a visitor to that beach might be unaware of them. How high would that be?
Let's look at this. So they drop a piece of dead fish onto the sand. And then you do a countdown.
And you wait. And you see one, two, three, four, five. And then you think, oh my God, maybe my beautiful bucolic beach vacation was actually sitting on top of tens of thousands of zombies. snails.
And it gets even cooler. I mean, zombie snails are kind of cool. But this is another nudibranch.
This is one that uses kleptoplasty. Kleptoplasty is when the genes that support, in this case, photosynthesis, are acquired by the animal and via horizontal transfer of those genes, the proteins are then, for photosynthesis, that should be coded for in the plastid, are actually shared between the animal and the plastid. So this is a case where a grazer, in this case the ELISA, had...
partially digested. Here's another. We've talked about the role of partial digestion in the bigger picture evolution of metazoans and the chimeric kind of theory of how we have mitochondria and plastids, that kind of a thing. This is another case where there are these, these are specifically animals, metazoans that can graze, but because they have retained undigested chloroplasts and because This is an intimate enough connection, and it's even somewhat species-specific, that there are species of this group of snails that have the genes for some of the facilitating photosynthesis with not any different algae or any different plant, but with some of them, the specific food types that they prey upon. So that facilitation is happening because of this tight kleptoplastic...
and essentially symbiotic relationship between the undigested chloroplast and the slug. It's amazing. And we thought there was one.
And of course, as you've seen in this course, if we think there's one, there's almost always more than one. And so what we're finding is that there's at least probably 20-odd species in three different genera that do this. And we're very interested in kind of exploring more and more about this because of our...
improving our understanding of symbiosis, but also for very applied reasons to understand. It's always for drug discovery, but lots of other reasons. As we're doing that, we unpack more and more stories. One of them you might have heard about in the New York Times a few years ago, which is when these sea slugs have lived for a long period of time for them, they undergo what is called an extreme autonomy, like a cephaloautonomy. they cut off their body, their own body, just behind the head.
This and that's what you're looking at. So this almost leaf-like shape, that's the whole bit of the mantle and the foot and all the rest of it. That's the majority of the body where the chloroplasts were embedded, where they were photosynthesizing, but which also becomes very heavily parasitized.
And so researchers have hypothesized that in addition, or one of the consequences of opening up and their... internal cellular architecture to that of another taxon has made them a little bit more susceptible to parasites. And one of the adaptations to deal with that parasite load is to cut off the body where all of the parasites are and go away from it.
And so this is an example of parasitic autonomy. Kind of amazing, again. Now, how are they moving?
If you've kept an aquarium, if you've had snails in your aquarium, you've seen some of these diagrams that are actually, these are demonstrating the kind of the waves of contraction that move across the foot. And so the large arrows are the direction of movement. So here we have, generally we have all of the snails kind of moving up from bottom to top. But you'll see different monotaxic, so like... parallel waves that go from front to back or from from back to front to help the snail move forward and retrograde like the limpet which would the waves proceed in the other direction and then there's kind of back and forth almost like a kayak paddling for the retrograde didactic and then these other more refined 1980s dancing style direct didactic waves for the neogastropod.
What does that look like in practice? Here, and this was the simple from the direct monotaxic. Kind of amazing. Hypnotic.
The mucus that they're laying down with that foot is important. We've bumped into snail mucus already because we've talked about it, particularly with trematodes. Earlier on when we were talking about platyhelminthes, we talked about the fact that snail mucus for...
Trematodes that are often famously using multiple taxa for their different life history stages. Snails laying down mucus, that's where lots of the eggs are or the larval stage that needs to attack the ant. Remember we talked about the ants that are neotenous. They're often attracted, the ants are, to eating the mucus.
So mucus itself is an adaptation of the snail to conserve water to help. move its body through space to defend against predators. Um, and then to. estivate or to be dormant.
If you didn't know, snails can very much be dormant. This is a Sepia numeralis, which is a snail that you've probably crunched across on the Guelph campus because they are everywhere all over the place. And this is one, and it's a European snail that has been moved into North America.
And if you go out into the dairy bush, say, I don't know, four or five days after a rain. So if you go out immediately after the rain, you'll find a lot of these things moving around because it's very humid. And the humidity means they're not losing water.
And so they can move around and do all the eating and the rasping that they're doing. But as soon as things begin to dry up, what you'll find is all hidden in the grooves of these trees along the central path of the dairy bushes. You'll find the snails stuck to the trees, glued there seemingly by their mucus that has dried out.
And what they're doing is estivating. They're waiting for that next kind of pulse of water. So the snail retracts into the shell and it secretes this mucus veil that they use to attach themselves to the vegetation. And they can stay for weeks, many, many long periods of time on the inside, moist, safe, and waiting for water to come back. And sometimes, so I said two or three.
four or five days, sometimes even two days without rain was sufficient to cause some of those animals to go into estivation. If you go along and you take your, in your planning of your career here at the university, if you take the field ecology course, the ecological methods course, the third or fourth year ones, this is kind of a lovely project to run in the dairy bush or in the other parts of the arboretum because... The moistures will change, the snails are easy to find and easy to count, and you'll get some data that you can analyze and get your good grade in that class too.
Now, reproduction, some of you know about this story already. Snails are kind of amazing. So, hermaphrodites, right?
And so they have, and this was documented by a Canadian researcher at McGill University named Ron Chase. And they have what are called... love darts.
So in copulation, there is a courtship between two individual snails, and they will use these love darts. One snail shoots its dart literally into the body wall of the other. And the idea, the hypothesis is by doing that, the dart shooter is stimulated to copulate, and the dart receiver is stimulated to either not change or to essentially engage its female gametes.
So one of them, just to which roles they are going to play. And so these darts are kind of gorgeous. Actually, there is Sepia hortensis. So this is the love dart that I'm moving my mouse over of a close relative of Sepia nemoralis, that banded snail that I encourage you to look for in the dairy bush. So all sorts of...
habitats over the world marine freshwater terrestrial benthic burrowing pelagic sessile interstitial there these animals exist everywhere and many things we talked about what they eat many things prey on them one of the things that you might not know that i love bringing up and sharing with you is that if you've enjoyed uh the interaction of luciferin and luciferase if you've enjoyed fireflies before that is fireflies The larval stages of fireflies are snail predators. And in fact, I have a video here from a few years ago. So what you're looking at, this is, with the pink segments there, this is the larva of the dry Lampyrid larval.
And its head is stuck inside the snail shell. This is in the leaf litter. in the rainforest at about 1200 meters.
So high elevation rainforest, not quite cloud forest. Now if we stay with the video for a bit, because I disturbed with my filming and my light, the head comes out. So you're looking at one of the last segments, and then if we wait till about in here. So you can see the jaws of the lampyrid, of the larval stage of the firefly, chewing on the foot, essentially consuming that snail. And it can be protruded into the shell.
They're zooming in, so we've got little antenna. And a shiny, there's the, you just got a good view of these mandibles that are just tearing apart the snail. So this is a nightmare movie for a snail. I should have warned you, don't show your snails this.
And this is, if you wanted to know even more about them, these are, though you saw it just very quickly in passing, but here's some of those snail nightmare lampyrid jaws. So next time you appreciate fireflies, appreciate the snails. that have fueled the fireflies because snails gave their lives for that firefly light.
A last bit about their reproduction. They can be depending on the taxa, gonocoric, or hermaphroditic. The love darts were for the hermaphrodites.
But the characteristic trochophore larvae characteristic of the of the mollusks is usually suppressed here and what we see is most frequently the villager larvae. And there's lots of diversity and so we're not going to have the chance to break this up. But there's lots of diversity in terms of parental investment. So there's some that brood their eggs. So they glue them to a surface and they stay around until the villager breaks out and swims away.
There's some that provide yolk. There's some that provide a protein egg case. But just to say, if you love, there's so many reasons to love the gastropods.
And I hope we've excited some of them in you today. Because we're going to move on. For the last, I see, 10 minutes, we're going to talk about the cephalopods. This is my disclaimer at the start.
I know for some of you, this is your favorite invertebrate group. We're going to be here for at least the majority of two lectures or the rest of this one and most of the next one. And I'm not going to be able to talk about all the things that you want to talk about.
I wish that I could. I often think that we need a mollusk course, that we could blow up this mollusk unit, these five or six lectures to an entire term. And in that term, we could spend five or six lectures just on cephalopods. Because they're kind of amazing. So what are the synapomorphies for this group?
Well, we're looking at a chambered shell, an internalized shell. In most cases, they have a hydrostatic organ, beaks, tentacles, extreme cephalization, camera-style eyes that you know about. So I'm going to park that often, so we're not going to talk a lot about it. A muscular mantle that has made a very distinct evolutionary change. A muscular foot.
that doesn't look like the feet of any other thing. They're pelagic. They're kind of raptoral. They're moving through the water.
One of the big changes there is diagrammed on the bottom left-hand side. So we think about this ancestral proto-gastropod. So this is pre- torsion, right?
This is a little thing moving around with its head and its ventral foot and its gill is facing, in this case, still facing posteriorly and we've got water going in and out over the gills. And so we've got a dorsal, an anterior, and a posterior. Now take a look at here.
And what we've got with a cephalopod is a foot that is the tentacles. And the posterior and the dorsal has lengthened. And so this functional anterior-posterior axis of the cephalopod really has changed how the organism, which parts of it are moving forward through the environment.
So there's a lengthening of this dorsal ventral axis, and that has to do with the primary function of the cephalopod body, which is this raptoral, swimming, predatory lifestyle. So there's the foot, and there's the head. So the foot has been transformed into a set of flexible, often or usually suckered prehensile appendages, arms and or tentacles that surround the mouth.
And in this case, the closest association of the arms and the mouth is responsible for the name, cephalopod, so the head foot, right? Gastropod is stomach footed, cephalopod is head footed. So the ventral region of the foot is another really kind of incredible adaptation, and that's this tubular siphon or funnel that exits the mantle cavity. And this is a lot of how they fly through the environment.
There's the siphon. And with another taxon with more octopoids here, you can see there's the funnel heading out of the siphon. And great big brain, lots and lots of cephalization. Many or all of you have seen My Octopus Friend. If you haven't, go look it up on Netflix.
Amazing documentary about the intelligence of these creatures. Thank you. And one of the final things that we're going to talk about, or the first things that we're going to talk about, and because it's maybe the most divergent group, is it's one of the oldest lineages of cephalopods, and that's these nautiloids. So the shell has been internalized for most of the extent lineages, like cuttlefish, squid, octopus.
You don't see it. It's internalized and it's practically gone. But for some organisms, like the nautiloid, and for some...
the amniots and many of the cephalopods that dominated the Devonian and the Ordovician and basically that Mesozoic era, these were ones that had ectococcalate. So the shell coils were external. They were a big part of the organism.
And so you've got the foot in its new formation of tentacles and arms protruding here, but it doesn't look like the extant cephalopods. So we still have some of these ectococcalate ones, these nautiloids living around the world today. We're going to talk a little bit about how they maintain buoyancy because it's kind of fascinating. And again, it falls under this, if a mollusk is given enough time in an environment, it will take advantage of the compounds and what it finds in the environment to its advantage.
So we've taken a bandsaw to an extant nautiloid shell here and an image and here in a diagram. And what you're looking at Two aspects here. One of them is the septum, so multiple septa that divide these shell chambers or cameral chambers that are inside the shell. So the organism lives only in the bottom most area here. And as it's growing, it's sealing off areas behind it.
And it maintains a connection with it that has a lined epithelial via that's called the siphoncle. Now the siphoncle here, that's the interior of this spiral, and you can see little bits of the connection here in the bandsawed actual version of the cephalopod here. So the siphoncle is an important part with the septum of providing this otherwise very heavy animal for getting up and off the substrate and being able to move through the water as a mobile predator that is still bearing this heavy. Protective, yes, but very heavy and an impediment to movement shell. So the siphoncle, the epithelia of the siphoncle is acting as an osmotic pump.
And it's removing, for one, it's removing liquid from the chambers, these cameral chambers in between these septa, and replacing it with gas to allow neutral buoyancy. And it's doing it because it's taking advantage of salts in the water. So the siphoncal epithelium is maintaining this high intracellular salt concentration, and it's hyperosmotic, and it's actively absorbing salt ions, chlorides, and sodiums from the camaral fluid, which is derived from the ocean water, creating this osmatic gradient, positive and negative gradient, across the chamber and into the siphoncal. And water is going to follow that gradient, right, and leave the chamber and enter the blood. the siphoncle with its epithelial lining and then as water is removed from any one of these septa lined off chambers the gas dissolved in the siphoncle diffuses into the chamber and replaces the water and so essentially chemical buoyancy is achieved and the heavy shell which permits protection no longer requires that the organism fall out of the water column but it's neutrally buoyant and it then can swim itself through the water, through the water column and maintain the starts of this predatory cephalopod lifestyle.
I think that's about as far as we're going to go today. This is a bunch of things, some amazing stories. We've got photosynthesizing snails. We've got snails that are using limpets, limpets that are using elements from their environment to... take care of themselves and to mirror the Cnidarian protected nudibranchs that are around them.
We have snails that are taking sulfides from deep thermal vents and building them into their shells to provide protection from the hot temperatures that are associated with the deep thermal vents. And then we've started talking about cephalopods and chemical buoyancy and then some of the... we're going to wrap...
continue that story our next time together. thinking about other elements of a predatory lifestyle that have affected the morphology and evolution of the cephalopods. So have a great rest of your week. I hope you enjoyed your lab exam and be good to yourself.
And be good to the others that are around you. Take care of yourself. Take care of them as well. And we'll see you next time.