← In Our Time
In Our Time
Seashells
00:53:29
The familiar sight in the sand that reveals the diversity and intricacy of marine life.
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- [00:00]
Helen Scales
This BBC podcast is supported by ads outside the uk.
- [00:06]
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- [01:01]
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- [01:25]
Melvyn Bragg
This is in our time from BBC Radio 4 and this is one of more than 1000 episodes you can find in the in Our Time Archive. A reading list for this edition can be found in the episode Description Wherever you're listening, I hope you enjoy the program. Hello, Botticelli's Venus emerging from a giant scallop shell Vishnu's sacred horn painting Panchajanya, the Aztec God Quetzalcoatl's talisman cut from a conch shell. Seashells appear in the mythologies of countless cultures. The urge to collect shells seems to be as old as our species. We've used them as decoration, currency, musical instruments. But shells aren't just beautiful objects washed up on our beaches. Many belong to one of the most diverse groups of the animal kingdom, growing remarkable shapes, patterns and str tell us about the Earth's oceans, past, present, and future. With me to discuss seashells are Suzanne Williams, merit researcher at the Natural History Museum Liz Harper, professor of Evolutionary Malacology in the Department of Earth Sciences and fellow at Gonville and Caius College, University of Cambridge and Helen Scales, marine biologist and author. Helen, I'm going to come to you first. The word seashells is not really a scientific term, is it? So what are we talking about when we say seashells?
- [02:57]
Helen Scales
Well, in my mind when we say seashells, we're talking about things that are made by a group of really diverse, abundant marine animals that are called mollusks. That's the big group name for them is molluscs. They're invertebrates, so they have no bones. They're soft, squishy things. But they tend to. Many of them live inside. They create a hard outer layer, an exoskeleton, and that is the seashell. It can serve lots of different purposes. First and foremost, really, it's their home. For many of them, it's a portable home they can carry around with them when they move. Many of them even have a front door which they can slam shut to keep predators out and to keep water in there as well. If they're the kind of mollusk that lives the shoreline and perhaps has to put up with the tide going out, these mollusks, they. They live all through the ocean. They are incredibly cosmopolitan. Everywhere from the deepest seas, extreme environments like hydrothermal vents.
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They.
- [03:55]
Suzanne Williams
They.
- [03:56]
Helen Scales
They swim through the water column. They occupy the shoreline. Those are the ones I think we know the best, really, because those are the shells that tend to wash up most easily on, on beaches. And then some of them made it into fresh water. Some came out onto land. Those are the. The slugs and snails. The slugs have lost their shells. But the snails that, that eat your vegetables and your flowers in your garden, you know, their ancestors were mollusks that lived in the sea. They live in forests. They live up top of mountains. I think the only thing mollusks that make shells that they haven't done, the only thing they haven't done is learn to fly. Pretty much everything else.
- [04:28]
Melvyn Bragg
So how have we humans used shells throughout history?
- [04:32]
Helen Scales
What's really incredible to me is just how deeply and globally seashells have been this really important part of human lives. And they've woven them for millennia, for countless millennia. And some of that is that there's a practicality to it. You know, we get a lot of food. People have eaten mollusks, clams, winkles, all sorts of things like that. Mussels. Exactly. Oysters. For, you know, for a long, long time, they've been important food. And we know about that often because the shells are what are left behind. And we get great big middens of those, and they fossilize well. And so we can look and see what people were eating in the past. And often the shells themselves are materials. They can be made choppers, scoops for getting water out of canoes, bailing out canoes, that sort of thing. But then there's this whole other side to shells, which goes even deeper into humanity really, which is the symbolism and the, the fact that people all around the world have found seashells or have been given them perhaps from somewhere far away and have instilled in them great meanings of all sorts of kinds. You know, often it's symbolisms of birth or death possibly linked to their white colour. A lot of shells have this white skeleton and that is a color that's very representative of both of those things also, I think, because they come from this hidden part of our planet, they come from down beneath the waves which is full of myths and monsters and creatures and things we're imagining. And possibly, you know, they come with those stories too. So we see them woven into human lives as grave goods. We see them buried with people going back again millennia. They're used as currency. They're used as the oldest forms of Jew we found. And we keep finding older and older ones and pushing that date back, you know, more than up to, I think at the moment, about 150,000 years as the oldest shell jewellery. So they've been with us, you know, and they've shown us now about what humanity has been like for, you know, for countless generations. They've always been with us and we've always been imagining things that they symbolize and that they, you know, they tell us.
- [06:39]
Melvyn Bragg
Liz Harper, let's get back to the mollusks themselves. How and why did they start to evolve these shells?
- [06:47]
Liz Harper
Well, that's a very interesting question. We don't really know terribly much about the very earliest shells because we're dependent on the fossil record. So there's been life on Earth for over three and a half billion years. But the first proper shells start about 540 or so million years ago during this grand Cambrian explosion. So that's when we see our first molluscs. Everything before that had soft bodies, so they don't preserve very well. So there's a sort of sense that we've almost missed the first shells because they don't fossilize, because they're probably very fragile and thin or maybe actually they've cheated, making them out of particles rather than laying down a shell. But we know that when they do start, that's the start of a sort of massive explosion, not just for the rest of animal life, but the mollusks themselves actually diversify and become more and more abundant from that time. So the big question really is, well, why do they start? Helen's mentioned many of the different uses these organ take for their shell. It's it's somewhere safe to live. Whether that's the first reason for having one is difficult to test. But it's clear that it is a form of armor, both from, if you like, storms and what have you. But most attractive to most people like me is predation. And at that time you do see the first evidence of predatory groups and the first evidence that predation is happening to these shells. So it's a popular idea at any rate, if maybe not the initial idea of having a shell, but very soon afterwards became co opted to being useful in that way.
- [08:29]
Melvyn Bragg
So, and what actually is a shell physically, what makes it up and how do you develop one if you're a mollusk?
- [08:37]
Liz Harper
So shells of mollusks are made of calcium carbonate and on the face of that, that's really good material. You can get it straight from the seawater, from disso calcium and carbonate, which comes from dissolved carbon dioxide from the atmosphere. So very easy building blocks. But it turns out actually that those minerals are pretty rubbish things to make armour out of. So it's very weak, it's very soft and it has a very bad habit of dissolving in acidic waters. So it seems like a really unpromising stuff. But the mollusks actually are much more ingenious than just laying down that mineral. So it's a biocompat composite they make. So the vast majority of it is calcium carbonate, but it's got a small proportion of organic material in it that is magic in it transforms the properties of this rather rubbish shell material.
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Melvyn Bragg
And it, they, they just, just to be clear, they process the calcium and the carbon together and then introduce the organics.
- [09:42]
Liz Harper
Yes, and they are usually laying down that those organics in the first place and that then controls and helps the calcium carbonate lay down in particular orientations and morphology. They have the most beautiful intricate microstructures which have various properties that the molluscs then use to their advantage. But that, that laying down the calcium carbonate is, goes on below an organic sheet, a thing called the periostracum that perhaps we might talk about again. But that organic layer on the outside of the shell is the first bit of the shell to be laid down. And that's the template onto which this magic biocomposite can then be laid and controlled. So it's very highly controlled by the animal. It's not, it's not something that happens by accident.
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Melvyn Bragg
And we can see the organic layer on, on top?
- [10:36]
Liz Harper
Yes, absolutely. Well, for many. So it varies quite a lot. So things like a mussel, if you think about seeing A mussel on the seashore. It very a thin brown layer on the outside that eventually wears off that might be several tens, maybe several hundreds of microns thick. Whereas things like oysters and scallops, it's very difficult to see that layer. It's tiny.
- [11:01]
Melvyn Bragg
Suzanne Williams, can you tell us about the differences between the different classes of mollusks and their respective shells?
- [11:09]
Suzanne Williams
Yep. The phylum mollusca, it's the second largest phylum of animals, the largest of the arthropods with insects and crustaceans. But molluscs have about 89,000 validly named extant species, so living, not fossil species. And of these, the phylum is divided up into seven classes. And of these, the absolute largest, by far and away, are the gastropods. And this group are your typical slugs and snails that you see in your garden. They account for about 76,000 validly named species. So this really is by far the biggest group. They live in the sea where they're most common, but they're also found in fresh water and on land. And many of them have shells. You have some that don't. So you have garden slugs and you also have nudibranch, which are beautiful, colorful marine slugs. But these ones produce the sorts of shells that we typically think of as seashells. So you get turbine shaped cells, top shells, spindles, limpets. All of those are gastropods. The next biggest group are the bivalves, and there's about 10,000 species in this group. And this group is found in fresh water and the sea, but not on land. And they have two shells and they're joined together by a hinge. So they're bivalves, two valves, and they mostly live in sediments. They burrow or bore into rocks. Those two groups really account for most of your seashells you're going to find. You might find, if you're very lucky, maybe a nautilus shell, which belongs to the class Cephalopoda, which includes octopus, squid and cuttlefish that don't have true shells. The only one in that group that does is the nautilus, which is a small group of about six or seven species. And they have a chambered shell that floats. So although the species is found offshore in deep waters, the shells will occasionally wash up or get caught in fisherman's nets. Then you have tusk shells, the scaphopods, scaphopoda, these are little tiny ones that are shaped like horns and they're open at both ends and they're quite fragile. But you do See them sometimes washed up in large numbers. There's the Polyplachrophora, which are the chitons
- [13:17]
Melvyn Bragg
we'll talk about, and we're going to talk more about them later on because they really are fascinating. But tell us also about the function of color. Color and mollusks is a fascinating subject. I didn't know up until quite recently, but it really is extraordinary.
- [13:36]
Suzanne Williams
It is amazing. One of the things that I think is really interesting is that we think of color as being something related to an object, but it's not an inherent property of an object. And this was something that took me a long time to get my head around. But it's actually the interaction between an observer who has an image forming eye, and a brain capable of processing the data and light reflecting off an object. So this leads to the really strange idea that we all call this red, but we will never know exactly what someone else is seeing. So the way we process data is unique to us, and the same is true for animals. So colors in the natural world either come from pigments, which are chemicals that either absorb some wavelengths of light and reflect others. Most colors that we see in shells are coming from pigments, but then you can also get color coming from structural color. And structural color is due to small repeating nanostructures that interfere with light. So some light gets transmitted and some wavelengths get reflected, but they also get amplified. So these colors can be really vibrant and really colorful. And you can also get iridescent color so that this changes with the angle of viewing. And one of the best examples of this is actually blue bird feathers. There are no blue bird feather pigments. All blue bird feather color is due to structural color. So if you could grind a feather up, a blue feather up as small as you can, enough to destroy these nanostructures, you will never get blue dust because those nanostructures aren't coloured.
- [15:11]
Melvyn Bragg
And maybe we'll talk also about what the function of colours are in shelves a little later on as well. Thank you, Suzanne. Helen Scales. Lots of us will be thinking of things like ammonites and those swirling spirals. What is that shape, the spiral? Why does it crop up so often in shell?
- [15:30]
Helen Scales
It's a lovely shape, isn't it? I did bring some shells with me and I've got a moon shell here. But if you grab, you know, look at a garden snail or find a shell in your house somewhere, and if you look at it from the top, you can often see that a snail shell has got this lovely spiral and it's mathematically, it's what we call a logarithmic spiral. And all that is really, if you imagine drawing that spiral shape in a two dimensional plane, start with your pen in the middle and sort of spin it outwards around that central axis. A log spiral is getting bigger each time you spin around one time. So it's sort of getting bigger at a constant rate. And that's really a just, I guess a phenomenon of how many things in nature are built, things that are spinning around a spot but getting bigger at the same time. So whether that's a shell or whether that's the, the arms of an expanding galaxy or the seeds in a sunflower, or a moth flying towards a candle, towards its doom, we see this sort of shape come up again and again. And I guess it is just that kind of fundamental. This is what happens.
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Melvyn Bragg
Is there some, I mean, is it particularly.
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Helen Scales
There must be something in the process of how shell, how molluscs make their shells, which they do throughout their lives. Actually, I guess that's an important point, which is unlike say crabs or lobsters, which have also got these hard outer layers, they moult them and they get rid of them, grow a new bigger one. And that's how their bodies grow bigger. Whereas mollusks keep the same shell their whole lives. The tiny central piece, the middle of that spiral, is the shell it had when it was a baby. And then it just kept making it bigger and bigger and expanding that open end, the circle, if you like. That's the open hole of a shell. A snail shell is where it grows from and it just keeps getting bigger. And I guess it is just that sort of rate of expansion keeps going and you. And voila, you get a spiral.
- [17:12]
Melvyn Bragg
Because we're talking about spirals. This might be the place to introduce poor Jeremy, the very lonely snail. Why was Jeremy a lonely snail? Who was he and what happened to him?
- [17:22]
Helen Scales
Jeremy, I think was very rare. Because the thing is, if you grab a shell and have a look at it, look at the next time you find a garden snail. Have a look. What way is that spiral turning? Look at it from the top again. Is it going clockwise or anti clockwise? Most mollusc, most gastropod shells are clockwise turning. They are right turning shells. But you get occasional rarities like Jeremy who spin towards the left. So he was a lefty. And the problem that comes with this is that it isn't just the shell that is spiraling in a certain direction. And the rest of the body is also asymmetrical. And crucially, the sexual organs are also offset. And certainly garden snails reproduce face to face. And so I like to think of it. The analogy I give is if you try to shake someone's hand and you both put out the same hand on the same side, it doesn't tend to work. So you've got to match. So poor old Jeremy needed a mate who was also left spinning garden snail. And a campaign went up. This is about 10 years ago now. We went out on the today program. The call went out for other left spinning garden snails and they found quite a few. And, and they were sent to the University of Nottingham where research was being done on Jeremy.
- [18:32]
Melvyn Bragg
And I gather, although he, he, he died soon after, he, he did witness the birth of his offspring.
- [18:38]
Helen Scales
There were some offspring. And actually this research has carried on and the people who've been looking into this are continuing to explore this idea of this left spiraling rarity. And they have discovered, they think that it's, it's, it seems to really be an accident early on in the development of the shell that something happens in the first few divisions of, of the mollusk when it's really tiny, that kind of sets it off in the other direction. And then once you get going, they keep going that way.
- [19:05]
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- [19:32]
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- [20:17]
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- [20:42]
Helen Scales
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- [20:46]
Helen Scales
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- [21:13]
Melvyn Bragg
Liz Harper can you tell us about mother of pearl and why it's so beautiful and why some shells have it.
- [21:23]
Liz Harper
So mother of pearl is technically called nacre and it is one of the very earliest types of shell structure that the mollusks use. And you find it across almost all of those classes that Suzanne talked about. So it's a really very important structure. It shows that beautiful iridescence because it's actually built of repeated tiny, tiny layers of a calcium carbonate mineral called aragonite. And they're about half a micron or so thick. They're nice hexagonal, I don't know, often about sort of 10, 15 microns across. And each shell is built of lots and lots of these on top of one another. And it produces this great iridescence. Probably for some reason that was explained to me in O level physics that I missed. So it scatters the light in some way. It's tremendously important material as far as the mollusks are concerned, because it is actually really very, very tough. So actually, if you think about trying to break something that's made of lots and lots of repeating tablets, then you either have to break each of those tablets in turn or the crack has to skip around them. And that basically sort of dissipates a lot of cracks that the fish or the crabs may be inflecting on your shell. So I don't think they have that nacre for themselves for colour. To demonstrate, it's usually covered up by other shell layers or this magic organic layer on the. Almost certainly a structural thing that they're using. But what's really interesting about that microstructure. So it's a really interesting thing that lots of material scientists are very interested in, how could we replicate what is actually a very low density but very tough material for things that we might want as humans. But interestingly, if you look at the mollusks as a whole, then actually fewer and fewer groups through time are using that wonder microstructure. They're using different microstructures. And so it's really fascinating to think about why, why do you get rid of it?
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Melvyn Bragg
Why, why would they discard something so useful as naca, mother of pearl?
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Liz Harper
Well, there's not a good answer to that or there's not a definite answer to that. But one of the things I talked about organic material being important, making, making the mineral work better in a shell. Nacre has a lot of organic material in it and it's probably that helps make it tough and a bit elastic. But we think that it's that organic component of a shell that's really very expensive metabolically for the animals to produce. And it's entirely possible that actually it's just the much easier to make a thicker, cheaper shell, which will do the job better and cheaper than laying this stuff down. But it's really interesting because all the different groups, almost the different groups use it and they've, they've all sequentially sort of lost it in large numbers.
- [24:20]
Melvyn Bragg
Thank you, Liz. Suzanne, back to color, which we were talking about before. Why do they produce these magnificent different colors, shapes, structures and, and so on, but in particular colors?
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Suzanne Williams
Oh yes, it's amazing. The mollusks are so colorful and so diverse, but color can serve different functions. It can serve visual roles and non visual roles. So Liz has listed one non visual role for iridescence, that is mechanical strengthening. The same is true for some pigments. So there are some very fragile jingle shells, bivalves that have carotenoid pigments and they increase the strength and elasticity of shells. And color can also help with temperature control and thermoregulation. So there's a flat periwinkle and the yellow morphs survive higher temperatures better than dark morphs. The pigments have also been implicated in things like wound healing, antimicrobial protection, protection from ultraviolet radiation. There's a lot of non visual roles it can serve, but there's also a lot of visual roles. And visual roles can be aimed at predators. They're often aimed at predators. And these include things like camouflage. So we have some shells like the emerald nerite, that's a beautiful green and matches the seagrass it lives on. You also have some where they're actually trying to warn off predators. There are no good reports of studies where they've shown this in shells. But cone shells are very venomous and they have very vivid markings. So it's possible that those are acting as a warning.
- [25:55]
Melvyn Bragg
What, the shells themselves or the mollusks
- [25:58]
Suzanne Williams
inside the shells themselves in this case. So it's possible that that's warning octopus and other fish and other things to stay away from. You also have things that mimic other things. So there are some shells that look like the hydroids they're sitting on. There's a limpet in the intertidal region where a lichen eats away the top of the shell down to through the first shell layers reveals some color underneath and makes it look like the open mouth of a barnacle. And the limpet lives next to barnacles and it's a really good hiding spot because the predators don't like removing the barnacles. They're hard work to get off. Whereas the limpets are easy. So by pretending to be a barnacle they're avoiding being eaten. But their colors themselves are much less likely to be used for intraspecific signalling.
- [26:42]
Melvyn Bragg
You mean amongst mollusks themselves?
- [26:44]
Suzanne Williams
Yes. So there's amazing examples of cephalopods. There's a lovely video of a squid that has put different colors on both sides of its mantle. Split right down the middle, it's showing an attractive color to a female on one side and a go away color to a competing male on the other side. But for shelled mollusks, the general opinion is they don't see colors. And for most species we've tested, they've got poor vision. But there are a few exceptions.
- [27:09]
Melvyn Bragg
Hold it. How do we know that molluscs have poor vision? How do you go about studying whether a sea snail can see well or not?
- [27:18]
Suzanne Williams
Well, it's really interesting. There's lots of different ways. So for humans and mammals and birds, you can dissect an eye and find that there are two different types of cells. There's cone cells and rod cells. The rod cells help you see in dim light. Cone cells are what you use to see color. And different types of cone cells have different photopigments. And you need more than one photopigment to be able to detect different colours. Humans have three different photopigments. Some animals have more and can see more colors than we can. Some animals see less. So dogs and cats only have two photopigments and their world isn't as colorful as ours. There have been tests on things like octopus and they've been shown to only have one photopigment. So we know that they can't see in color. But invertebrates don't have rods and cones, so we can't look for those. But you can tell in different ways. You can still look at the anatomy of the eye and work out their spatial acuity. But to work out whether they see color or not, you have to do different tests. So if you do it genetically, you can identify the proteins involved, but that is. That doesn't always tell you if they see in colour, but it can tell you if they don't see in colour. The best way is behavioural studies.
- [28:27]
Melvyn Bragg
Wow.
- [28:27]
Liz Harper
Thanks.
- [28:29]
Melvyn Bragg
It's quite extraordinary. And Helen, we've learned about the colours. What about the patterns? Is there any rhyme or reason behind the patterns on shells?
- [28:38]
Helen Scales
As far as I know, this is one of the big puzzles of molluscs that we don't really have a very good explanation for some of the patterns. For instance, I do have, again, I have a cone shell with me and the patterns on this one are lots of repeated triangles, a sort of tooth pattern. You can have a look at it if you like. It's good and dead. Don't worry, it's not got any poison in it. And anyway, as Suzanne said, possibly they're trying to say I'm really dangerous. But the thing about cone shells, there's about 800 species and they have got incredible variety in the patterns on their shells. They are a collector's favorite. They have been for ages. People have always wanted, you know, these beautiful shells. They can be much bigger than this one's, only sort of thumb size, but they can have stripes and spots and zigzags and all sorts of things going on. And these. Yeah, they're nocturnal species. They generally live in the seabed during the day. So it's the question also is, what's going to see these things at all? And it is a big puzzle, firstly, how do they make these patterns? And that's something that people have looked into and there have been various theories and kind of computer models that have looked at how you might create patterns like that. Possibly through the combination of different chemicals, maybe hormones sort of diffusing through the tissue that makes the shell. Or possibly it's under neural control. There could be nerves that are bouncing off each other, sort of switching on and switching off pigment production. I should say the patterns are being made a bit like an inkjet printer, for the most part, as the shell is being made on that open edge, the newest bit of the shell, a line of pigment can be laid down at the same time. So, you know, you get a line of ink on a inkjet printer, the next line adds up and up and you get a picture at the end of it. So that's essentially, for the most part, what molluscs are doing. Yeah. And so there's theories, it could be that natural selection has just been let off the hook and it's just running wild. There's no reason to it. But one theory I do quite like, and again, I don't know if we've got any proof that this is the case, but it's a possibility, is that actually these are. They're essentially the mollusc writing down notes to itself to remind itself where it left off the last time it was making more shell. Because not all molluscs are constantly making shells. They are kind of doing it seasonally, when the temperature is favourable, when there's food around and there will be stop starts in that production. As you can imagine, we've talked about these intricate spirals and the shapes, other shapes as well, that molluscs grow their shells into. You need to know where you left off, otherwise it's just going to become an absolute mess. There is some hint, I think, that maybe the pigments are somehow they can be sensed by the mollusks. They can sort of almost taste perhaps where they were before, line themselves up and carry on making more shell before we leave.
- [31:18]
Melvyn Bragg
Vision and eyes. Suzanne, tell us about chitons. We mentioned them before. What are they? This is truly weird.
- [31:27]
Suzanne Williams
Yeah. Molluscs have the most amazing diversity of eyes of any group in the animal kingdom. But chitons might be the weirdest. So chitons are the little. They're a long oval shape. They have eight interlocking flat plates and a strong muscular girdle that holds them together and they clamp down tight on rocks. And they live mostly in the intertidal or shallow waters. They have little networks of tunnels through their shells. Then they have lots of sensory organs that pierce through these shells. But some species actually have eyes in their shells. So these sensory networks include eyes. So the same material that is used to make the shell is used to make the eyes. So some of the eyes actually rub off and abrade against rocks and they grow new ones as their shells grow. And the new eyes are bigger than the old eyes.
- [32:17]
Melvyn Bragg
Liz, going to talk about a different animal now, the hermit crab. Now the hermit crab, of course we all know lives in other animals, shells. Can you tell us a bit about what happens when hermit crabs grow? Because presumably they outgrow their shells, their homes.
- [32:37]
Liz Harper
Well, in that case they have to find a new shell. And so that's. It was again back to the kind of economics we were talking about beforehand. There's an economics involved in hermit crabs and houses. So they fight over Shells, but they sort of fight over shells, queue up to take other people's shell of a crab shells. So it's, you know, they need the shell because actually they're not crabs in a way that, you know, the true crabs are, that you're probably more familiar with. They squat lobsters and things like that. And they've actually avoided, they've cheated. It's economics again. They've cheated from making a nice hard carapace of their own, which costs a lot of energy by using the dead shell of a snail. But in that case, they absolutely, if they're going to grow, they need a new shell to move into because they have a sort of slightly pathetically mineralized shell of their own and they won't last past their own predators. So, yeah, it's a really important economic moment for a hermit crab. Is the shell big enough to move into?
- [33:40]
Melvyn Bragg
Helen, can you describe what happens when they all collectively.
- [33:44]
Helen Scales
Absolutely. I mean, I should just also say if you ever see a hermit crab, if you're snorkeling and you ever happen to see one do hang around, you might watch it trying to sort of try on another shell. And seeing them pull their naked bottoms out of their shells is quite something. It's really odd. I think the most interesting, well, the kind of have the most wonderful picture in my mind of what hermit's crabs get up to are the hermit crabs that let you live on, on land. And so for them, the supply of shells is even harder to come by. And they scuttle down the beaches to see what they can find in the, in the flotsam and jetsam. And what will happen if a big shell shows up, a big empty shell that looks like it might be good? Hermit crab will come along, take a look at it, size it up. If it's too big for them at that point, they'll actually just sit next to it and wait. For up to 24 hours, they will sit and wait and then probably other hermit crabs will wander along and take a look. And they might also think it's a bit big for me too, but I'll hang around and you kind of get a spontaneous hermit crab party breaking out. But then they're very ordered and very, very careful about what they do. And around this large shell you'll get lines of hermits sort of in size order, one next to the other, next to the other because they're looking at each other, they're feeling each other's shells up, figuring out who's the biggest, who's the smallest, and then the biggest ones at the top will be fighting over the empty shell, figuring out who's going to get it. The smaller crabs down the end of the lines are behaving like supermarket shoppers and hedging their bets on which queue is going to go first and who's going to get this shell. And they're dodging between the queues. And then eventually the largest hermit crab will come along. They'll say, yes, this is going to be my shell. They will take that shell, cast off their old one, and that gets passed on down the line. So it's like a, it's like a vacancy chain, which you get with things in the human world too. But everybody gets a new shell, one size bigger, everyone goes off happy.
- [35:26]
Melvyn Bragg
Suzanne, you've got a huge collections that you administer at the Natural History Museum. How do you go about collecting those shells? I mean, do people just pick them up from the beach or do you go searching for them more actively?
- [35:42]
Suzanne Williams
Yes, our collections are really huge. We have 8 million specimens and we still continue to collect. And when we collect nowadays, it's often with the idea of having material that we can use for molecular studies. So that means we need to collect the animal as well as the shell and we need to be able to preserve the animal. So we anesthetize the animal and then we use different methods. So the simplest one is just to crack the shell so that the preservative penetrates. But that means the shell is destroyed. So we want to keep the shell intact where possible because this is a really important character for us. Other methods. There's a method that thousands of years old that has been used for people when they're eating, or shell collecting. And the Japanese call it nikku, niki, if I've pronounced it correctly. You pour hot water on and you can actually unwind the snail from the shell and pull it out intact with your shell all intact. But if people are thinking of collecting themselves, they need to remember that check about permits, because some dead shells in some places you need permits to collect them, you need permits to transport them between countries. And there are some real dangers in collecting seashells. Believe it or not, some seashells, as we mentioned, the cone snails, are deadly venomous. If these snails, some of them, the geography cone snail eats fish in nature. And if you think how slow a snail goes and how fast a fish goes, it has a harpoon that it fires at it and the toxin it has is so venomous and so fast acting that the fish doesn't get any further away. And the snail can go over and eat it. That toxin, if you get stung by one of them, you don't have very long to live. And the nickname in the Philippines for this is the cigarette fish, because you have just enough time to smoke a cigarette before you die. Another thing to really be careful of, especially if you're in Australia or places like that. I grew up worrying about this. Well, my mum worried about this when I was a child. Blue ringed octopus, really small, tiny, pretty little octopus will sometimes use shelves to hide in. And there have been lots of reports of these shells being picked up by children, taken home in the bath. And then the blue ringed octopus drops out and these octopus will give a completely painless bite. They have like a parrot's beak and they'll take a little bite, you don't feel that, but it injects tetrodoxin venom. And one little octopus that is enough to sit in the palm of your hand, small enough to sit in the palm of your hand has enough toxin to kill at least 10 adults.
- [38:06]
Melvyn Bragg
Well, I won't be going anywhere near a blue ringed octopus, I can assure you. Liz, how have researchers used these vast collections of shells in, in museums? What have we learned from them?
- [38:18]
Liz Harper
Well, we've learned a huge amount because it's an amazing resource. So you can imagine going in the field and braving the, the horrors that Susanna has just been talking about. But you know, it takes time and it takes money. In museums you are able to leverage huge amounts of effort that people have put in over sort centuries often. So you have a vast sort of covery of coverage of different sort of species environments which have disappeared through sort of habitat destruction. And my favourite thing these days is to look at historic collections. We're very interested in the way the environment is changing because of human activity. And it's very interesting and some of my students have been involved in doing this, is actually looking at historic collections from the same locality where it's been collected and has gone into a museum maybe every decade for the last hundred plus years. And you can then actually look to see if those shells have changed, how thick they are, how they grow, all sorts of things like that. So it's a real way of sort of conducting an experiment but without having actually planned it. So it's really. And you can't do that without museum collections.
- [39:30]
Melvyn Bragg
Helen, you talked about the human uses, our relationship with shells earlier. What can you tell us about shell money?
- [39:38]
Helen Scales
Money again, I'm going to bring out my collection. This one actually, you can Sort of
- [39:41]
Liz Harper
hear, what have we got?
- [39:43]
Helen Scales
I've brought some cowries. So cowries are these lovely little shells that you get around the world. The ones here in Britain are tinier small than this. This is the tropical species. So one of the reasons I think that shells have been used as currency is that they. They have that kind of nice feeling in your hand. You can count them out and hold on to them, stick them in your pocket. They're durable most of the time, difficult to fake. So, again, it's one of these extraordinary things that human cultures around the world have repeatedly used shells in various forms as a form of currency, whether it's whole shells like cowries, whether it's pieces of shell ground down into beads and woven together into bigger, bigger structures or looped into great big long strings. But the cowrie in particular, these ones have a really extraordinary story connected to them, which is a really, really dark part in human history, which is the link to the trade in enslaved African people. When I first heard about it, it just blew my mind that this. This. This trade was tied into billions and billions of shells. So essentially, this was going on for hundreds of years. Traders from Europe would be going into Southeast Asia, to India and Sri Lanka and places like that and. And filling up their ships with. With fine silks and spices and such like. And those goods were actually. Didn't take up all the space that they had on these ships, and they needed something to almost just to weigh the ships down as ballast. And there was a cheap local source in the Indian Ocean of cowrie shells. They were collected in the Maldives and the islands in the central Indian Ocean. And that was a tradition that had been going on for a long time. And they had been used locally in India and other places as a form of small currency. But it was the European traders who came along and thought, oh, actually, we could make use of that. So they would buy up very cheaply huge numbers of these shells which the Maldivian people were collecting from the seas, and then those shells would go on their own very long journey. They would go around the African continent, back to Europe. Then they would be unloaded with all these spices and tea and everything else, loaded back onto ships that then went back down to the African continent, to West Africa, where ultimately they were exchanged for human lives. And these became the money. Tens of thousands of these things per human head. And that went on and on, and billions of these shells were essentially swapped for people.
- [42:01]
Melvyn Bragg
Thank you, Helen. Liz, a final question to you. What are the main threats that mollusks and Their shells face nowadays?
- [42:10]
Liz Harper
Well, I'm afraid it's probably us. So habitat destruction is happening all the way around the world for various reasons. We have a very bad habit of transporting mollusks as larvae in the ballast water of ships and they go on little trips around the world with the ships and then are discharged into new environments. And sometimes, sometimes those mollusks just re establish in those new habitats. But of course the main thing that's worrying us at the moment is that we're worried about get temperature increase and increased acidity of the seawater. And if you lay down a shell made of calcium carbonate at least the fear is that they may be dissolving very fast. It's probably actually even.
- [42:57]
Melvyn Bragg
You mean their shells?
- [42:58]
Liz Harper
Yes, the shell shells are dissolving. And if we assume that they, as we do, as we, as we believe that the shell is very important to them as armor, having expended a lot of energy to lay it down only to have it dissolve is pretty critical. Many of them can actually. It works out in experiments that we can actually keep up with it quite well. They compensate. That sounds really good. It sounds like the snails might be winning in the shell's dissolving, but they're laying down more shell. But that's probably not quite the way of thinking about it. It's not such a good answer because of course in laying down new shell again they're using energy and that's energy they're not using to grow or reproduce. So although it seems on the face of it a very happy story, we have to think about that as well.
- [43:45]
Melvyn Bragg
But Helen, it's not too late to turn it around, you think?
- [43:48]
Helen Scales
No, absolutely. And one of the other things that mollusks do is when there's lots of them living together, they can create really important habitats. We get things like mussel reefs, oyster reefs and sure, yes, we've lost a lot of that habitat here in Britain. I think we've probably lost something like 95% of the native oyster reefs that used to fringe the fringe, fringe this island of ours. But now there's a lot of awareness of that disappearance. Whereas before, you know, a couple of generations ago probably didn't even realize there used to be such enormous habitats. And lots of efforts are being made to put oysters back in the ocean and to find ways of rewilding, if you like that word. There are other. A really extraordinary habitat we have up in Scotland are flame shell reefs. These are little clams that make nests in the seabed. They create these little sticky fibres and sort of hold the seabed together combined with bits of sand and grit and things, and they have these bright orange tentacles sticking out, which is why they're called flame shells. And one particular place in Loch Caron in Westeros, there was a while ago it was clear that scallop dredgers were coming in and really destroying this really important habitat that's placed for nursery for other animals to grow up in. But when that damage was noted, an emergency marine protected area was put in place, which can happen if there's an important ecosystem, important species that's in trouble. And already within about five years, we were seeing recovery of that habitat and you know, a spreading even of this amazing flame shell reef. So it absolutely can happen. The ocean is very capable of recovering and growing back to abundance. We just have to give those species a chance.
- [45:23]
Melvyn Bragg
A note of optimism to end on my thanks to Suzanne Williams, Liz Harper and Helen Scales. In Our Time now takes its annual break. We'll be back on the 17th of September. Have a good summer and thank you for listening.
- [45:38]
Helen Scales
And the In Our Time podcast gets
- [45:40]
Liz Harper
some extra time now with a few minutes of bonus material from Misha and his guests.
- [45:46]
Melvyn Bragg
Now, clams. How are they able to keep. I mean, they're so tight clam shells, you can't open them.
- [45:55]
Thumbtack Advertiser
No.
- [45:55]
Suzanne Williams
That. That's a myth.
- [45:56]
Melvyn Bragg
Is it?
- [45:57]
Suzanne Williams
Yes. This is something.
- [45:59]
Helen Scales
Giant clams. Yes.
- [46:00]
Suzanne Williams
Only people. You talk about giant clams.
- [46:01]
Melvyn Bragg
I'm talking about any old.
- [46:02]
Suzanne Williams
Oh, no. Clams. Sorry. I'm talking giant cl.
- [46:04]
Melvyn Bragg
Well, tell us about giant clams then.
- [46:06]
Suzanne Williams
It's a myth that people our age and older know and younger people don't. Because it used to be in all the old Tarzan movies and everything that they would go diving. Yes. And he would get his foot trapped in the giant clam and be unable to escape. I worked on giant clams for three years and used to go collecting samples and I accidentally dropped a weight in one once and I thought, oh, this is really bad for the poor clam. So I put my arm in up to my shoulder of this giant clam and it's trying. Cause I felt like a vent wet and can't close. Not the really big giant clams. They're slightly smaller. That's a tridactnogy.
- [46:42]
Melvyn Bragg
Scallops and oysters though.
- [46:44]
Suzanne Williams
Yes. They can tote very tightly, very tight.
- [46:46]
Helen Scales
It's got very strong muscles.
- [46:48]
Melvyn Bragg
So. So they've got this huge muscle by the valve, presumably. I mean, by the.
- [46:53]
Suzanne Williams
They call it ducta muscles. And they actually hold the shells close.
- [46:56]
Helen Scales
You can see the Scars, Right. So you see how big the muscles are from the shape that's left on the inside of a shell.
- [47:01]
Suzanne Williams
So when you eat a scallop, that's what you're eating. You're eating the adductor muscle.
- [47:05]
Melvyn Bragg
It's the muscle.
- [47:06]
Suzanne Williams
It's the muscle you're eating.
- [47:09]
Helen Scales
Watch out
- [47:11]
Suzanne Williams
if you get the whole animal. Some of them have got amazing blue eyes.
- [47:16]
Helen Scales
They do. I've been looked at by scallop.
- [47:20]
Melvyn Bragg
We didn't talk about the snails with the weird eyes.
- [47:24]
Suzanne Williams
Can I tell you about Ali's project? My student, she did an amazing behavioral study on craft conch snails. She was both our students, Liz's as well. Conch snails have got these really amazing eyes on really long mobile eye tentacles. And they're huge eyes. In fact, I would suggest look up conch snail eyes. And you can.
- [47:41]
Melvyn Bragg
How are we spelling conch there?
- [47:42]
Suzanne Williams
C O, N, C, H. And she did behavioral studies to work out what they can see. So she took one snail and Velcroed it in place so it wouldn't move around. And then she put a tent around it.
- [47:52]
Melvyn Bragg
She Velcroed it?
- [47:54]
Suzanne Williams
Yes.
- [47:54]
Melvyn Bragg
In place?
- [47:55]
Suzanne Williams
Yeah. She just put it. Well, no. A little strap. A little strap over it. He was quite happy. He was just Velcroed so he couldn't walk away. Then you put a tent around, and then you showed it a computer screen with a dot that got bigger and bigger and had a camera above to film its behavior. And then what happened is, as the dot gets bigger, at some point it can see it. And it starts responding to it. It stops feeding, first of all. Then it partially withdraws its proboscis and its eye stalk, and then it withdraws them entirely. And you can work out from the video the times those happen and from the program how big the circle was. And then. And then you can work out how well they can see. And it turns out these particular ones see really, really well. They can see as well as rats and better than worker bees. And we think part of the reason is because they've evolved a really unusual operculum, which is the little door that closes behind them.
- [48:42]
Melvyn Bragg
Thank you.
- [48:43]
Suzanne Williams
But they use it like a walking stick in this group. And they can move along in a really jerky jumping motion.
- [48:50]
Melvyn Bragg
If you look on the Internet for mollusks moving, there are some very, very strange animals. Quite exciting to watch.
- [48:59]
Helen Scales
Oh, yeah.
- [48:59]
Liz Harper
Scallops are good. Swimming.
- [49:00]
Helen Scales
They're good.
- [49:01]
Suzanne Williams
Yes.
- [49:01]
Helen Scales
And we haven't talked about sea butterflies. They fly. They do fly through the water. And they've got Little instead of one little foot, they slither around on, they've got, they break it into two and flip the round.
- [49:10]
Suzanne Williams
It's like Dumbo.
- [49:10]
Liz Harper
If you've seen the film, it's epic.
- [49:12]
Helen Scales
And they're teeny tiny.
- [49:14]
Melvyn Bragg
And then of course they're able to dig.
- [49:17]
Liz Harper
Yes.
- [49:17]
Helen Scales
Really fast as well.
- [49:18]
Liz Harper
Like razor fans and snails.
- [49:20]
Melvyn Bragg
Yeah. Anything else we, we missed out?
- [49:25]
Suzanne Williams
Well, you barely scratched the surface. I guess.
- [49:31]
Helen Scales
I'd love to talk about that. We're still discovering species as well and that, you know, we've got tens of thousands we already know, but more being found all the time. A lot of them in the deep sea. One of my favorites is the scaly foot snail which lives on hydrothermal vents. These extreme hot springs that have heat to hundreds of degrees and extraordinary habitats, but full of life. And the scaly foot snail is one of those found in the Indian Ocean in around 2000, I think. And they have this weird thing that their shells are made out of what seems to be an iron based compound and their feet are covered in scales. They have this sort of weird looking scaly armor. And when they were first discovered, I think people generally, scientists generally assumed that armor, that iron based shell and the scales were some sort of defense from attack. Attack from the outside. But actually it turns out that they're defending themselves from, from an attack from within. Because like many things that live on hydrothermal vents, they have symbiotic microbes living inside their bodies. That's how they get their food. These are tiny, you know, cells that are using chemicals in the water to grow essentially rather than sunlight. And these microbes inside the snails, they're very good, they provide food. But then a byproduct of this food production is sulfur. And sulphur is a key ingredient in slug pellets. And it's very dangerous, poisonous for snails. So actually the scales have this again, a nanostructure in them, a bit like the nacre we talked about. A lot of it comes down to these nanoscopic structures in the shells. They act like little tailpipes on a car exhaust and they draw that sulphur out of their body and it reacts with iron in the water around them and lays down this iron layers. So in fact it's the snail protecting themselves from this sort of internal poison so that they can exist in this crazy place.
- [51:10]
Melvyn Bragg
Well, I refer the listeners to an earlier episode of ours on Archaea who hang around thermal vents a lot.
- [51:19]
Helen Scales
There you go.
- [51:20]
Melvyn Bragg
Suzanne, can you tell us the story of Tyrian Purple?
- [51:24]
Suzanne Williams
This is a really amazing story. So Tyrian purple is a pigment that comes from snails from the family Myricidae, and it's named after the ancient Phoenician city of of Tyre, where it was produced on industrial scale, although it actually originated much earlier in Minoan civilizations. It was mostly harvested from three species in the Mediterranean, from Hexaplex Trunculus, Bolanus brandaris and Stramoneta haemostoma. And the dye comes from this tiny, specialized organ called the hypobranchial gland. And in the wild, these animals are predators, so they eat barnacles and mussels and they secrete this secretions from this hypobranchial gland onto their prey and it makes them relax, which means that they don't have to drill them, so it saves them energy to do this. They also produce these secretions to get rid of predators because it has this muscle relaxing properties. They also put it around their eggs and it's thought to have antimicrobial properties. There is no purple dye inside the hypobranchial gland. It's a colourless precursor to the dye. But if you cut it open and expose it to light and sun, enzymes act on it and it will change color. You'll see it going from colorless to milky white to yellow, green to green to blue to purple. The final pigment is called 6,6 Prime Dibromo Indigo. And it's the bromine atoms which the snail takes up from seawater that actually gives huge stability to this pigment. So unlike other pigments that were available at the time that would wash out in the laundry and fade in the sun, this actually gets brighter and more vibrant in sunshine. And there's some recipes. Pliny the Elder recorded a recipe and mentioned how dreadful the smell was. And I can personally testify that rotting pigments smell absolutely disgusting. But layered on top of that, there was garlic, stale urine, and the numbers they had to process were huge. They had to either dissect out the gland or crush the snail. And a scientist in 1909, he managed to reproduce this dye and he used 12,000 snails to produce 1.4 grams of this dye. And because it was so highly valued and so difficult to make, it was considered extremely valuable. And it was worth way more than gold. And because of that, it was only used by the kings and priests and really important people. And that's where we still use this phrase, born to the purple, which is used by Julius Caesar, Cleopatra, Nero, and
- [53:56]
Melvyn Bragg
of course, popes and cardinals. And popes and cardinals as well. Yes, Liz, I was Interested in what you said about how molluscs are adapting to greater acidity in the water. But presumably we're now seeing changes in temperature and changes in acidity at a scale that evolution surely will have a struggle keeping up with. Even if you're a hardy aragonite mollusk,
- [54:27]
Liz Harper
it depends how fast paced that particular species lives. I think so many mollusks only live for very short periods of time. So one year, two years, and in that case there's quite a lot of energy in the tank for adapting. I think the problems are the slightly longer live lived mollusks. So one of the key thing, well, is that there are some mollusks that will live not only decades, but centuries.
- [54:54]
Melvyn Bragg
Yes, let's. Talking of which, let's talk about our friend Hafron. Yes, the. The clam who was born in 1498 or 1499, just before Da Vinci started work on the Mona Lisa. Tell us about Hafren.
- [55:13]
Liz Harper
So Hafren was dredged off Iceland. People have always been interested in that species. Its scientific name is Arctica Icelandica, and they've always known it lives for a long while. So it's really interesting because these, all the mollusks we're talking about really lay down growth lines which are a bit like tree rings. And so there's lots of environmental information we can get from tree rings or shell rings. And so people have always been interested in this particular species. So it was actually colleagues in Bangor who were working on this, trying to develop what's called sclerochronology, which is equivalent to dendrochronology in the oceans. You cut the shell up and you can count those rings and you can work out how many years they live. A little bit of uncertainty about exactly how old it is, because when clams grow in the first year or so, they tend to grow continuously and therefore they don't have these breaks, so you can't count them.
- [56:09]
Melvyn Bragg
Ah, here comes Martha with an offer
- [56:11]
Helen Scales
for tea, tea or coffee orders.
- [56:14]
Liz Harper
A black coffee would be nice.
- [56:16]
Helen Scales
I'll have a tea, please.
- [56:17]
Suzanne Williams
White coffee.
- [56:18]
Helen Scales
Black coffee.
- [56:18]
Suzanne Williams
White coffee.
- [56:19]
Helen Scales
Tea In Our Time with Misha Glennie was produced by Martha owen. It's a BBC Studios production for Radio 4.
- [56:27]
David Baddiel
Hello, I'm David Baddiel and from Radio 4 and the History Podcast, I'm hosting 60 Years of Hurt, a series about football and Englishness in which we try and define what Englishness actually is via the roller coaster history of the England men's football team. It includes contributions from various English gentlemen and Stephen Fry, David Seaman, England sports psychologist, Pippa Grange and many others. England may or may not win the World cup in 2026, but maybe you'll find out why it means so much to us as a country that they might do listen to 60 Years of Hurt on BBC Sounds
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Helen Scales
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