Section of Mollusks

August 2, 2024 by Erin Southerland

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

Imagine you’re a clam, hanging out in your cozy little hole under shallow ocean water, with your siphon out, just filtering lunch out of the water current, happy as a…you. Then, all of a sudden, something flips you gently out of that hole.

You pull in your siphon and your foot, clamp shut your valves. You’re pretty tough to get open, strong adductor muscles keep your two shells held tightly together, and you’ve survived danger by closing up shop and waiting before. And nothing seems to be trying to pry you open, even though something has wrapped itself around you, and is now pulling you down into the sand with it. Then:

scrape scrape scrape

Or imagine you’re a young moon snail, Neverita duplicata – one of the most common species of moon snails that live on the eastern seaboard of North America. You’re a gastropod with a lovely round grayish shell, such that people call it a “shark eye,” and you’ve got a huge foot that can come out of that shell and cover almost all of your body – or all of your prey’s body! But at the moment you’re just cruising along the sand, slurping at a bit of detritus. Suddenly, you’re enveloped by something. You instinctively pull your body into your shell and tightly close your door-like operculum for safety. Then your aperture is covered by…something familiar? Then:

scrape scrape scrape

It doesn’t matter how tightly the clam clamps, or how mighty the young snail’s foot, both are going to come to the same fate, slowly.

scrape scrape scrape

Eventually, your shell is penetrated. A rasping radula – a mollusk’s organ containing its teeth – has bored a hole through your shell with the help of a gentle acid secreted by a gland by the mouth, and then you feel a burning: gastric juices are being pumped through the hole to begin to digest your flesh. Your killer begins to slurp you up, right where you lie, wrapped up in their hug, as you’re slowly eaten alive.

The young moon snail might have figured out who its killer was before the end: that’s how it eats too. The thing is, moon snails are cannibals, the larger preying on the smaller.

There are hundreds of kinds of moon snails all over the world, but the ones that are probably most familiar to beach goers on the eastern coast of the USA are two species also commonly called “shark eyes” – Neverita duplicata and Euspira heros. From the top, they’re hard to tell apart (the spire on E. heros is a little pointier than on N. duplicata) but once you flip them over, it becomes easy to distinguish them: N. duplicata, the Atlantic moon snail, has a big callus over its umbilicus, and E. heros, the Northern moon snail, doesn’t. Technically, only the Atlantic moon snail has a shark eye shell, but since they’re often mixed up with Northern moon snails, the term shark eye is sometimes applied to them too.

N. duplicata, left; E. heros, right. *Photo credit: Sabrina Spiher Robinson*

These two moon snails aren’t the only marine gastropods that drill their prey and digest them alive to suck them up for dinner – lots of marine gastropods are predatory drills. But moon snails have distinct boreholes that allow people to identify when a shell has been bored specifically by a moon snail – scientists can even tell the difference between the Atlantic and Northern species’ holes. These “countersunk” holes look like little funnels, wider on the outside of the shell than on the inside. Other kinds of drilling snails leave behind straight-sided holes.

These unique boreholes allow scientists to track the evolution of moon snails from the Miocene to recent times. One group of researchers found that moon snail cannibalism might have driven a kind of coevolution between and among moon snail species. Because one moon snail can make dangerous prey for a fellow moon snail predator, over time moon snails seem to have learned to drill other moon snails at a spot on their shells that allowed the predator to cover the prey’s entire aperture, preventing the strong foot of their prey from fighting back. This means boring through a thicker part of the shell, however, so it takes longer to hold down and bore through the prey snail’s shell. But the record of natural selection in fossils throughout time suggests the added cost must be worth the benefit of moving target drilling zones. Meanwhile, small moon snails almost always lose out to larger ones when attacked, so both N. duplicata and E. heros have evolved to get bigger and bigger over time – although a bigger snail is also a more enticing snack target. Same-sized moon snails don’t even bother to attack one another, suggesting that a fellow moon snail is just too dangerous a prey when the winner of the battle between snails is a toss-up. As evidence that these are often battles between predator and prey snails, there are many incomplete boreholes found – a moon snail started attacking another moon snail, but only managed to get the job halfway done before the prey moon snail escaped. [1]

To be fair, moon snails aren’t just vicious cannibals – they also enjoy the snail equivalent of a nice salad. Another study that analyzed the tissues of moon snails revealed that their bodies have the chemical signatures of omnivores. The technique is called stable isotope analysis, wherein scientists use the ratio of carbon and nitrogen isotopes in an animal’s body to determine its diet, in broad terms. Carbon exists in three isotope forms, meaning the number of protons is the same in all three atoms, but the number of neutrons is different in each (carbon-12, carbon-13, and carbon-14); Nitrogen also has three isotope forms, nitrogen-14, nitrogen-15, and nitrogen-16. The vast majority of carbon on Earth is carbon-12, which is a stable isotope, as is carbon-13, meaning they do not decay over time; nitrogen-14 and -15 are stable, and make up the vast majority of nitrogen atoms. Different plants and animals have different ratios of carbon and nitrogen isotopes. The ratios of isotopes in plants and animals differ and these differences transfer to the body of the consumer, and so the isotope ratios of a meat-eating animal will differ from those of a vegetarian animal, and an omnivorous animal will be different again. Scientists were surprised to find that wild moon snail isotopes suggested they also ate non-animals, so to check their findings they fed captive moon snails nothing but clams, and then tested their isotopes – which looked exactly as one would expect in an all-meat diet. Apparently the wild moon snails were actually eating things other than meat, probably algae. This was a big deal, since so much of the literature on moon snails is about their predatory drilling! [2]

Moon snail shells are a relatively common find on east-coast beaches (and another moon snail, Euspira lewisii, is a common find on the west coast), but if you’re at the beach this summer, there’s more to look for than just shells – moon snails also leave behind very distinctive egg nests, often called “sand collars.” The fertilized female snail nestles into a little hole in the sand (as all moon snails do during the day when they’re not feeding) and produces a sheet of mucus, which she mixes with sand and pushes up to the surface, as she does so, the sheet curls around her shell and eventually right around to form a ring. This fusion of mucus and sand grains solidifies, she attaches her thousands of eggs to it, and then covers those with another layer of mucus and sand. Once the eggs are ready to hatch after a few weeks, when the next high tide comes along the eggs let go thousands of little larvae called veligers, which will drift off to finish developing into baby snails who will eventually settle into the intertidal zone and start lives for themselves. Once the eggs hatch, the collar becomes brittle and disintegrates, but if you find one that’s still plastic-y on the beach, leave it! There are thousands of tiny baby vicious predators in there waiting to hatch! Awww.

*A sand collar full of shark eye eggs. Image credit: Blenni, Public domain, via Wikimedia Commons.*

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks and Tim Pearce is Head of the Section of Mollusks at Carnegie Museum of Natural History.

References

[1] Gregory P. Dietl and Richard R. Alexander, Post-Miocene Shift in Stereotypic Naticid Predation on Confamilial Prey from the Mid-Atlantic Shelf: Coevolution with Dangerous Prey PALAIOS Vol. 15, No. 5 (Oct., 2000), pp. 414-429

[2] Casey MM, Fall LM and Dietl GP, You Are What You Eat: Stable Isotopic Evidence Indicates That the Naticid Gastropod Neverita duplicata Is an Omnivore. Front. Ecol. Evol. 4:125. (2016) doi: 10.3389/fevo.2016.00125

Oysters Swim Towards a Siren Soundscape

by Sabrina Spiher Robinson

illustration of a walrus and a person on a beach looking at oysters with feet — *Illustration by Sir John Tenniel. Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License.*¹

“’O Oysters, come and walk with us!’

The Walrus did beseech.

‘A pleasant walk, a pleasant talk,

Along the briny beach:

We cannot do with more than four,

To give a hand to each …

Four other Oysters followed them,

And yet another four;

And thick and fast they came at last,

And more, and more, and more—

All hopping through the frothy waves,

And scrambling to the shore …

‘O Oysters,’ said the Carpenter,

‘You’ve had a pleasant run!

Shall we be trotting home again?’

But answer came there none—

And this was scarcely odd, because

They’d eaten every one.”

In 1872, Lewis Carroll included the poem “The Walrus and the Carpenter” in his classic book Through the Looking Glass. The Walrus calls out to the oysters to join him and the Carpenter on a walk along the seashore; the young oysters don’t know any better and come to join him. Eventually, all the oysters are eaten up. But can one really sing a siren song to make an oyster come to them? An informed answer to this question requires some background knowledge information about an underappreciated form of wildlife.

oyster shells on cultch in a box — *The favored subsurface described as “cultch” is depicted in this cluster of oyster shells of the species* Crassostrea virginica.

Oysters live in reefs, submerged ridges or mounds of stable material, and baby oysters prefer to settle on a base — called “cultch” — of old oyster shells. Where conditions are favorable, oysters have plenty of company. When a team of researchers investigated the diversity of oyster reefs in the Gulf of Mexico, they detailed the incredible number of creatures that live on the reefs where oysters form: 115 species of fish and 41 species of crustaceans made the Gulf oyster reefs their homes, at very high densities and in communities containing up to 52 species at a time. Other researchers have documented multiple corals, mollusks, and worms that live primarily on oyster reefs. Unfortunately, erosion from coastal development, wetland destruction, unsustainable harvesting, and pollution have decimated populations of the Atlantic coast’s native oyster, Crassostrea virginica, which is bad news for coastal marine habitats in general.²

The importance of oyster reefs as marine habitats for multiple species is only one reason to preserve and reconstruct them. Oysters, as filter-feeding animals, provide an incredible service to the water quality of the estuaries they inhabit. They are also, of course, an important food source along America’s east coast.

The complications of rebuilding and repopulating oyster reefs are many. Pollution must be reduced, especially the run-off of agricultural fertilizers. Such fertilizers “enrich” underwater environments in a process called eutrophication.

Eutrophication causes massive blooms of algae that set off a chain of events disastrous for bodies of water and their inhabitants: the algae can release toxins on its own, but most commonly it overwhelms host ecosystems by blocking sunlight and killing all of the other plants in the water. Eventually the algae die too, and as all these dead plants decay, eaten away by multiplying bacteria that use up what little oxygen is left, dead zones form that suffocate underwater animals. This decay also lowers the pH of the water, leading to acidification that harms and kills animals (especially mollusks, whose shells dissolve in a very acidic environment). Additionally, if sediment erosion is not reduced, these water-borne materials eventually bury and suffocate oysters.

Oyster bed substrates that have been destroyed by human construction or aggressive commercial dredging can be replaced with cultch that is attractive to baby oysters. However, baby oysters must be recruited to the rebuilt reefs, either from the natural population of oyster larvae, or from hatchery-grown larvae reintroduced to the environment.

So, how to attract a baby oyster to your newly constructed oyster reef? First, let’s consider the life cycle of C. virginica, and the critical importance of age range in young oyster populations. In the first year of their adult lives, oysters are male. At certain times of the year, in response to pheromonal cues from their fellow oysters on the reef, they release clouds of billions of sperms. Older oysters on the reef, creatures transitioned into females after a year or two of life, release millions of eggs into these clouds of sperm. About two days after an egg is fertilized, the oyster larvae have become what are called veligers, and they begin to feed on particles in the water and to seek a place to call home. During this time, they develop a foot, and once they arrive on some promising substrate, they can crawl around, looking for just the right spot. At this point they are called spat. Soon the spat lose their feet and cement themselves to the spot they will call home for the rest of their lives, which can be more than a dozen years in the wild.

small boxes of oyster shells — Crassostrea virginica, from the CMNH collection, multiple shells that look completely different, but represent a single species. Epicures report taste differences according to where exactly each oyster lived.

It was long unknown how much choice an oyster veliger had in determining where it landed. Until the 1990s scientists thought that baby oysters had very little control over their movement in the water. In 2022, Australian scientists studying the Australian flat oyster, Ostrea angasi, proved that oyster veligers could very deliberately move to get to a surface they preferred to make their permanent home on.³

How this discovery occurred is of particular interest. The Australian researchers were testing the effects of soundscapes on oyster larvae, following experiments conducted in America in Pamlico Sound in North Carolina. Soundscapes are the collective sounds of a given environment: all the noises of human and non-human animal activity, along with environmental sounds of wind and water and precipitation. In 2014, researchers in North Carolina were experimenting with ways to attract oyster larvae to their newly built conservation reefs. They discovered that by recording the soundscape of a healthy oyster reef and playing it in the water, they attracted a much higher number of spat on experimental tiles near the recordings. Apparently, the baby oysters heard the sound of a healthy oyster reef and headed towards it to make their homes.⁴

How do oysters hear? Humans and other land animals hear through a system of air compression. Sound waves compress air in certain patterns, and tiny hairs within our ears translate those compressions into electrical signals that are then sent to the brain for further interpretation as sound. Underwater, animals hear through particle vibration: sound waves vibrate from particle to particle in the denser medium of water, where the particles are in direct contact with one another, even the water contained in the bodies of fish and invertebrates. Underwater animals have sensing structures that translate these vibrations into electrical signals that the animal then interprets in some way.⁵

Following up on the work of the North Carolina scientists, the Australian scientists confirmed in lab studies using underwater speakers in a completely currentless body of water, that oyster larvae were deliberately swimming towards the sounds of a healthy reef to settle. When they tried this technique on human-made conservation reefs, oyster recruitment increased on the artificial cultch — an important finding, since if baby oysters don’t find the newly deployed conservation reefs quickly, the reefs become covered in algae, making it very difficult for oyster spat to attach to them.⁶

And so, recording and replaying the soundscape of a healthy oyster reef — populated by snapping shrimp, oyster toadfish, and many other creatures that call a healthy oyster reef home — can help with the recruitment of baby oysters to human-made reefs for the purposes of conserving and growing the endangered population of C. virginica. Not only can oyster larvae “hear,” they can — and will — very deliberately swim toward the sounds of a healthy reef. And truly, who amongst us could deny the siren song of the snapping shrimp and the oyster toadfish?

Listen:

Coastal Conservatory

Center for Marine Sciences and Technology (CMAST)

Sabrina Spiher Robinson is Collection Assistant for the Section of Mollusks at Carnegie Museum of Natural History.

Notes:

Science Museum Group. Magic lantern slide depicting Alice’s Adventures in Wonderland, Walrus, Carpenter and Baby Oysters. 1951-316/11Science Museum Group Collection Online. Accessed 9 January 2024. https://collection.sciencemuseumgroup.org.uk/objects/co8362656/magic-lantern-slide-depicting-alices-adventures-in-wonderland-walrus-carpenter-and-baby-oysters-lantern-slide.
La Peyre Megan K., Aguilar Marshall Danielle, Miller Lindsay S., Humphries Austin T. Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis Frontiers in Marine Science, Vol. 6, 2019 https://www.frontiersin.org/articles/10.3389/fmars.2019.00666
Williams, B. R., McAfee, D. & Connell, S. D. Oyster larvae swim along gradients of sound. Journal of Applied Ecology, Vol 59, 2002, pp. 1815–1824 https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2664.14188
Ashlee Lillis, David B. Eggleston, DelWayne R. Bohnenstiehl Oyster Larvae Settle in Response to Habitat-Associated Underwater Sounds PLOS ONE 9(1). October 30, 2013 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079337#amendment-0
Nedelec, S.L., Campbell, J., Radford, A.N., Simpson, S.D. and Merchant, N.D. Particle motion: the missing link in underwater acoustic ecology. Methods Ecol Evol vol 7, 2016, pp. 836-842 https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12544
McAfee, D., Williams, B. R., McLeod, L., Reuter, A., Wheaton, Z., & Connell, S. D. Soundscape enrichment enhances recruitment and habitat building on new oyster reef restorations. Journal of Applied Ecology, vol. 60, 2023, pp.111–120 https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2664.14307

Clams in the Concrete! How Old is this Sidewalk?

Mollusk shells persist long after the death of the soft-bodied animals whose secretions formed the protective covers. These sturdy remains can inform us about species living in an area at that time. Many mollusks occur in specific habitats and during certain time periods in Earth’s history. When we find mollusks in sediment with dinosaur bones, for example, we receive a clue about the geologic age and habitat in which those dinosaurs lived. When mollusks first appear in an area, deposits containing their shells allow us to estimate when events in Earth’s history occurred, including archaeological events, or even relatively recent construction projects.

This morning as I walked across the Panther Hollow bridge near Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, I noticed clam shells in the concrete of the sidewalk. What can the presence of these clam shells tell me about how long that sidewalk has been there?

tip of boat shoe on sidewalk near clam shell for scale

clam shell embedded in concrete — Top: Clam shell in sidewalk on Panther Hollow Bridge. Bottom: Close-up of clam shell, inside view. Scale in mm.

Concrete is a mixture of cement with sand and gravel. When sand and gravel are taken from rivers, this natural resource sometimes contains clam shells. I believe the clam shells in this sidewalk were scooped up along with the sand and gravel to make the concrete. Then after the sidewalk was poured, but before it fully hardened, the clam shells floated to the upper surface.

As an aside, information about comparative densities is instructive here. Two common crystal forms of calcium carbonate are calcite and aragonite, which have different densities (calcite 2.71g/cc, aragonite 2.93). Most mollusks form shells of aragonite. However, shells are not pure aragonite, containing small amounts of protein and other substances, so clam shells can have densities around 2.5-2.6. In comparison, the density of quartz, which makes up much of the sand used in making concrete, is 2.65. The clam shells are slightly lighter than the sand, which probably explains why they floated up to the sidewalk surface.

I identified these clam shells as Corbicula fluminea (common name: the Asian clam). They have the characteristic shape and size, the outside has strong regular growth ribs, and on the inside, the lateral teeth bear minute serrations. This species was first recorded in North America in British Columbia about 1924. As an invasive species, it has spread, through human activity, to at least 46 US States.

close up of clam shell embedded in concrete — Top: Outside view of clam showing strong ribs. Middle: Partly broken clam, inside view showing external rib impressions in concrete below. Bottom: Close-up of clam’s lateral teeth showing minute serrations. Scale in mm.

When did the species appear in southwestern Pennsylvania? There is a record of Corbicula fluminea in 1979 from the Ohio River just downstream from Pittsburgh and another in Greene County, southwestern Pennsylvania from 1981. Museum records of this species became more common after about 1993, suggesting that the clam probably became more common about then.

top of clam shell on blue background — *Corbicula fluminea* collected in 1993 from Loyalhanna Creek, Southwestern Pennsylvania. Top: inside of shell. Bottom: outside of shell showing strong ribs. Scale in mm.

Consequently, I conclude that the Corbicula fluminea-containing concrete sidewalk on the bridge next to Carnegie Museum must have been poured after the late 1970s, and possibly after 1993, when the clam became abundant in freshwater of western Pennsylvania, the region where Pittsburgh is located.

Museum collections provide useful information about when non-native species arrived in an area. Now you know that one of the many uses of mollusks is estimating ages of things.

Although some people might think of clams as an abstract concept, here is an example of clams in the concrete!

Timothy A. Pearce, PhD, is the head of the mollusks section at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Vampire Squid: Cutest Dracula

The Vampire Squid is your go-to mollusk for Halloween. It’s covered with glow-in-the-dark spots, and it can hoist its cape-like webbed arms over its head to transform into a pumpkin shape complete with outward-pointing fleshy spines. But wait, there’s more. With the largest eyes relative to body size of any animal, this has got to be the cutest Dracula you ever saw. And the scientific name, inspired by the cloak-like webbing and the dark body color, literally translates to “vampire squid from hell.”

Vampire Squid, showing cloak-like webbing between arms, large eye, and ear-like fins. [Image from Wikimedia Commons]

The Vampire Squid (Vampyroteuthis infernalis) is an extreme deep-water cephalopod more closely related to octopuses than to squids. It is so bizarre that scientists classify it in its own taxonomic order, Vampyromorphida, to show that it differs markedly from other living cephalopods. Like octopuses, it has 8 arms with webbing between them, but unlike octopuses that have suckers on the entire length of the arms, the Vampire Squid bears suckers only on their outermost half. The prominent feature on the arms of the Vampire Squid are fleshy spines or cirri. In addition to the eight arms, it has two velar filaments, in pouches in the webbing, that are analogous (and maybe homologous) to the two long tentacles of squids.

Regarding superlatives, the Vampire Squid has the largest eyes relative to its body size of any other animal, a detail noted in the Guinness World Records. A fully-grown individual can be 28 cm (11 inches) long with eyes 2.5 cm (1 inch) in diameter. Adding to the cuteness factor, they have adorable ear-like fins, which adults use for swimming; juveniles also have fins, but primarily use jet propulsion to move around.

They live in the lightless ocean depths 600-900 m (2000-3000 feet) deep in temperate and tropical oceans world-wide. The ocean at these depths is an oxygen minimum zone with so little dissolved oxygen that most complex organisms cannot survive. But the vampire squid survives perfectly well with a low metabolism and blue blood that is more efficient at carrying oxygen than that of other cephalopods. They use ammonium in their tissues to regulate their buoyancy (ammonium is a wee bit lighter than water), reducing the need for active swimming. Living in the oxygen minimum zone probably helps it to avoid predators.

If disturbed, the Vampire Squid kind of turns itself inside-out into the “pumpkin” or “pineapple” posture by curling its arms and webbing up to cover the body with the spiny cirri pointing outward. Their body is covered by photophores, or light-emitting organs, which they can use to flash a wide range of patterns. In the pumpkin pose, they conceal most of the photophores, but they can light up the tips of the arms and wave them around to distract predators. If it gets really annoyed, the Vampire Squid can release a sticky cloud of luminous mucus that glows for nearly 10 minutes, presumably long enough for the Vampire Squid to make a get-away into the inky darkness.

Vampire Squid, underside of arms showing fleshy spines. [Image from Wikimedia Commons]

Much of what we know about their behavior comes from videos made by Remotely Operated Vehicles. It is hard to keep Vampire Squids alive in aquariums at the much lower pressure of our human world, but the Monterey Bay Aquarium succeeded for a while and has some great videos. Aquarium scientists were able to solve the mystery about what the Vampire Squid eats. No, it doesn’t eat blood! It eats detritus (organic debris), also known as marine snow. As the Vampire Squid drifts in the current, any debris that touches an extended filament is moved by the creature’s arms to its mouth. Unusual for being the only known cephalopod to eat non-living food, the Vampire Squid is adapted to eat material that falls through the oxygen minimum zone. Marine snow includes dead bodies, feces, and a lot of mucus from above, and because of the mucus, it is sometimes jokingly referred to as marine snot.

I imagine if Dracula learned about the Vampire Squid, he might exclaim, “I thought it was eating blood, but it’s snot!”

Snails in the Desert

Land snails are leaky bags of water that survive on dry land. Snails lose water through evaporation, and because mucus is more than 90% water, they must expend water just to move, gliding on their silvery slime trails. Most land snails occur in moist environments where they can readily replenish lost water. But some snails live in the desert or other arid areas! How is that even possible?

Several strategies help snails survive in arid situations. For example, some close their aperture with a door or with a mucus sheet, some have small apertures or modify their growth direction to make better seals, some have mucus that inhibits evaporation, and some manage moisture loss by choice of microhabitats.

Fig. 1. Two *Clydonopoma poloense* snails from Dominican Republic showing their opercula. (Photo by S.P. Aiken with permission.)

An operculum, or door, closes the shell in some land snails (Fig. 1), although most land snails lack one. The operculum is attached to the rear of the snail’s tail; when the snail pulls into its shell, the tail withdraws last and positions the operculum to make a tight seal. In addition to protecting the snail from water loss, it also protects from predators.

Fig. 2. Two *Helix pomatia* edible snails from Russia (CM154077) with apertures closed by an opaque epiphragm. (Photo by T.A. Pearce.)

Snails that don’t have an operculum can cover the aperture with a mucus sheet called an epiphragm. In most snails, the epiphragm is thin and clear, but in some species, the epiphragm can be thick and opaque (Fig. 2). During dry periods, snails can form an epiphragm over the aperture or they can make a tight mucus seal between the aperture edges and substrates such as a rock or plant. The seal helps to retard evaporative water loss. Some snails in the desert remain sealed under a rock for years before a rainstorm wakes them.

Fig. 3. *Coelocentrum gigas* from Guatemala CM62.8574 (left); *Achatina zebra* from Africa CM62.6917 (right). Land snails in drier areas tend to have relatively smaller apertures like the shell on the left. Shells pictured are 8 and 8.5 cm tall, respectively. (Photo by T.A. Pearce.)

Snails of arid areas usually have a relatively small aperture (Fig. 3). The smaller surface-area-to-volume ratio reduces moisture loss through evaporation. Just like you would lose less heat (on a cold day) with your parka zipped up and your hood cinched around your face, the snail loses less water with less of its skin exposed, as in the case of a smaller aperture.

Fig. 4. *Ganesella fusca* (left) from Japan (CM106167) and *Zachrysia guanensis* (right) from Cuba (CM152889). Land snails in drier areas tend to have greater change in direction of growth when reaching full size, allowing the plane of the aperture to make a closer seal with flat surfaces. (Photo by T.A. Pearce.)

As growing snails approach their final size, many dip the direction of shell growth toward the shell base (Fig. 4). This results in the plane of the aperture making a tighter seal on a flat surface. Snails of arid areas tend to have shells that make tighter seals on flat surfaces than snails of moister areas.

Fig. 5. Urocyclid semi-slug from a dry area in N Kenya. (Photo by T.A. Pearce.)

The mucus of some species retards evaporation. Snails produce different kinds of mucus, for example, the mucus they glide upon to move, sticky or distasteful mucus when irritated, and mucus on their skin that can retard evaporation. One day when I was traveling in northern Kenya during the dry season after at least 6 months without rain, I was surprised to find a semi-slug (a gastropod whose shell is too small to fit the entire body) resting among some dry leaves and soil (Fig 5). It must have had special mucus covering the body that retarded water loss, allowing this species to survive many months of aridity.

Finally, snails influence their moisture loss by choosing their microhabitats. Some snails burrow underground during hot, dry weather to escape the heat. Other snails crawl under moist logs or descend deep into rock piles to avoid the harshest weather.

Why would snails even choose to live in the desert? I’m not sure anyone knows the answer for sure. My guess is that snails might live in a desert because it allows them to escape predators or competitors who can’t or don’t want to live there.

How do they do it? Snails survive in the desert by leaking water a bit more slowly than snails in moist areas.

First ever American Malacological Society virtual meeting, 13-14 July 2020

During two days in mid-July the American Malacological Society (AMS) held its 86^th annual meeting over Zoom because of COVID-19 concerns. The occasion marked the first time the organization, whose members study mollusks, convened the gathering virtually. Attendance was greater than recent in-person AMS meetings, perhaps because of the low cost of the event (no travel or accommodation costs) and its appeal to people who shun air travel for its immense carbon footprint. There were more than 150 participants, 49 formal presentations, and 18 posters. Remarkably, thirteen presentations were by students.

As usual I enjoyed hearing about my colleagues’ research, rejuvenating old friendships and making new ones, and simply talking with people who already know that mollusks are vitally important. One surprising piece of information I learned from colleagues is that Carnegie Museums of Pittsburgh are ahead of other museums (e.g., Field Museum, University of Florida Museum) in re-opening to the public. Bravo to CMP!

The talk I presented summarized a publication I co-authored with Heather Hulton Van Tassel, Assistant Director of Science and Research at CMNH. The presentation, titled Is acid precipitation a factor in the decline of the terrestrial tiger snail, Anguispira alternata, in northeastern North America?, “was well-received and elicited some insightful questions. You can hear a 12-minute recording of the talk here:

Current plans are to hold next year’s AMS meeting in Nova Scotia, but if the COVID-19 virus remains a threat, and with the successful outcome of this year’s meeting, we might gather virtually.

The Moon Snails Neverita duplicata and Euspira heros: Cannibal Predators of the Sea! … who also enjoy a nice algae salad

by Sabrina Spiher Robinson and Tim Pearce

References

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