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8 Fascinating Facts About Seashells

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Bloomsbury

When wandering the beaches this summer, have more to say about the shells you find than why you can hear the ocean in them. Marine biologist Helen Scales’s Spirals in Time: The Secret Life and Curious Afterlife of Seashells is packed full of interesting facts about seashells and the creatures that create them. Here are just a few you can use to wow fellow sunbathers this summer.

1. MOLLUSKS MAKE ONLY ONE SHELL.

Mollusks use calcium carbonate and proteins, secreted from their mantles, to build their shells. As a mollusk grows, so does its exoskeleton. “They are among the few animals on the planet that wander around carrying with them the same body armor they had as babies; the pointy tip or innermost whorl is the mollusk’s juvenile shell,” Scales writes. “Day by day, the mollusk shell slowly expands, making room for the soft animal growing inside.”

2. MOST SHELLS OPEN TO THE RIGHT.

Although there are some species with shells that are always sinistral, or left opening, nine out of 10 shells are dextral, meaning they open to the right. Because of their rarity, “shell collectors go crazy” for sinistral specimens, Scales says, “so much so that over the years clandestine trades have prospered in fake lefties.”

Though shell collectors might love them, there are dire consequences to being a sinistral animal: Mating with dextral mollusks is pretty much impossible. To see what happens when lefties and righties tried to mate, researchers placed pairs of left- and right-opening Roman snails in tanks. “No matter how much the left-right partners are feeling in the mood,” Scales writes, “the slurp of a baby snail’s feet never issues from mating cubicles.”

3. SHAPE MATTERS.

Seashells can be plain and smooth (think clamshells) or come adorned with spikes and ridges and protrusions. Both shapes serve a purpose. Elaborate shells come from the tropics, where predation is fierce. Geerat Vermeij, professor of paleoecology at UC Davis and author of A Natural History of Shells, believes that mollusks in the tropics evolved these ornaments to ward of predators—a much better option than creating a big, thick shell, which will keep predators at bay but is also a pain to make and drag around. He also thinks that “the pleats and corrugations on many tropical shells are a cost-effective way of creating a strong body armor that’s difficult to break into while keeping the weight down,” Scales writes. "Thickening and flaring out the aperature of seashells is another way of deterring predators.”

Sleeker mollusks, meanwhile, can use their streamlined shape to move without detection and to get away quickly. A shell’s shape can also keep the mollusk from sinking in sand and mud, or to keep them anchored in it.

4. THE PATTERNS ON SHELLS AREN’T RANDOM.

Recent research suggests that the elaborate colors and patterns on shells are, Scales writes, “not frivolous playthings but important registration markers for shell-making that have been subject to the forces of natural selection, and have evolved over time.” In other words, mollusks might use the patterns to figure out where to put their mantles to continue making their shells. Scientists still aren’t sure what kinds of pigments the mollusks are using.

5. THE OLDEST KNOWN HERMIT CRAB USED AN AMMONITE SHELL.

There are nearly 1000 species of hermit crab existing today, which rely on old seashells from dead mollusks to protect their soft abdomens. (Interestingly, according to Scales, hermit crabs never kill the current occupants of the shells; they wait until the mollusk has died, and let other animals do the eating, before they take over.) The oldest known hermit crab fossil was discovered in 2002, in the Yorkshire, England village of Steepton. Paleontologist Rene Fraaije spotted the crab in the shell, which, Scales writes, belongs to an ammonite, “an extinct cephalopod that swam through far more ancient seas, in the Lower Cretaceous around 130 million years ago. After it died it sank down to the seabed where a crab scuttled past, picked it up and climbed inside.” It’s the only one found in an ammonite so far.

6. NO TWO ARGONAUT SHELLS ARE THE SAME.

For a long time, scientists believed that argonauts stole their thin, iridescent shells from other animals. Jeanne Power, who invented the aquarium in 1832 so she could study argonauts, discovered that the animals are born without shells and, when they reach about the size of a pinky nail, begin to make their shells. But unlike other mollusks, which secrete their shells with their mantles, female argonauts use glands in two of their arms to make, and repair, their shells. (Male argonauts don’t make shells.) Because of all that repair work, no two argonaut shells are the same.

Argonauts—the only octopuses that still have a shell—can come completely out of their shells, which have ribs and ridges that reduce drag as they move through the water. They use their suckers to hang on, and they’ll never completely abandon their shells. If you take its shell away, an argonaut will die.

7. ONE OF THE OLDEST KNOWN SHELL COLLECTIONS WAS FOUND AT POMPEII.

The collection was preserved in the eruption of Mount Vesuvius in 79 AD and consisted of “shells that came from distant seas, certainly as far as the Red Sea, that seem to have been kept for the simple reason that they looked pretty,” Scales writes. 

8. THAT SHELL YOU BOUGHT ON VACATION? IT WASN’T COLLECTED ON A BEACH.

“Plenty of shells are left behind by mollusks that died of disease, predation, old age, or some other fate, but those ones don’t stay pristine for long,” Scales writes. “Chances are that your gleaming shell was taken from a living animal; it was collected and killed and its shell removed and sold into the shell trade, so that ultimately you could buy it.” No one is sure how many shells are traded each year, though it’s thought that around 5000 species of mollusk are targeted. And that trade is very likely affecting wild populations; in some areas, species of mollusk have smaller shells than they did in the past, “a strong indication that not all is well and the larger specimens have been depleted.” When buying shells, be sure to avoid large species like the nautilus (which take a long time to reach maturity, don’t have many young, and are already over-hunted)—or don’t buy at all.

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15 Confusing Plant and Animal Misnomers
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People have always given names to the plants and animals around us. But as our study of the natural world has developed, we've realized that many of these names are wildly inaccurate. In fact, they often have less to say about nature than about the people who did the naming. Here’s a batch of these befuddling names.

1. COMMON NIGHTHAWK

There are two problems with this bird’s name. First, the common nighthawk doesn’t fly at night—it’s active at dawn and dusk. Second, it’s not a hawk. Native to North and South America, it belongs to a group of birds with an even stranger name: Goatsuckers. People used to think that these birds flew into barns at night and drank from the teats of goats. (In fact, they eat insects.)

2. IRISH MOSS

It’s not a moss—it’s a red alga that lives along the rocky shores of the northern Atlantic Ocean. Irish moss and other red algae give us carrageenan, a cheap food thickener that you may have eaten in gummy candies, soy milk, ice cream, veggie hot dogs, and more.

3. FISHER-CAT

Native to North America, the fisher-cat isn’t a cat at all: It’s a cousin of the weasel. It also doesn’t fish. Nobody’s sure where the fisher cat’s name came from. One possibility is that early naturalists confused it with the sea mink, a similar-looking creature that was an expert fisher. But the fisher-cat prefers to eat land animals. In fact, it’s one of the few creatures that can tackle a porcupine.

4. AMERICAN BLUE-EYED GRASS

American blue-eyed grass doesn’t have eyes (which is good, because that would be super creepy). Its blue “eyes” are flowers that peek up at you from a meadow. It’s also not a grass—it’s a member of the iris family.

5. MUDPUPPY

The mudpuppy isn’t a cute, fluffy puppy that scampered into some mud. It’s a big, mucus-covered salamander that spends all of its life underwater. (It’s still adorable, though.) The mudpuppy isn’t the only aquatic salamander with a weird name—there are many more, including the greater siren, the Alabama waterdog, and the world’s most metal amphibian, the hellbender.

6. WINGED DRAGONFISH

This weird creature has other fantastic and inaccurate names: brick seamoth, long-tailed dragonfish, and more. It’s really just a cool-looking fish. Found in the waters off of Asia, it has wing-like fins, and spends its time on the muddy seafloor.

7. NAVAL SHIPWORM

The naval shipworm is not a worm. It’s something much, much weirder: a kind of clam with a long, wormlike body that doesn’t fit in its tiny shell. It uses this modified shell to dig into wood, which it eats. The naval shipworm, and other shipworms, burrow through all sorts of submerged wood—including wooden ships.

8. WHIP SPIDERS

These leggy creatures are not spiders; they’re in a separate scientific family. They also don’t whip anything. Whip spiders have two long legs that look whip-like, but that are used as sense organs—sort of like an insect’s antennae. Despite their intimidating appearance, whip spiders are harmless to humans.

9. VELVET ANTS

A photograph of a velvet ant
Craig Pemberton, Wikimedia Commons // CC BY-SA 3.0

There are thousands of species of velvet ants … and all are wasps, not ants. These insects have a fuzzy, velvety look. Don’t pat them, though—velvet ants aren’t aggressive, but the females pack a powerful sting.

10. SLOW WORM

The slow worm is not a worm. It’s a legless reptile that lives in parts of Europe and Asia. Though it looks like a snake, it became legless through a totally separate evolutionary path from the one snakes took. It has many traits in common with lizards, such as eyelids and external ear holes.

11. TRAVELER'S PALM

This beautiful tree from Madagascar has been planted in tropical gardens all around the world. It’s not actually a palm, but belongs to a family that includes the bird of paradise flower. In its native home, the traveler’s palm reproduces with the help of lemurs that guzzle its nectar and spread pollen from tree to tree.

12. VAMPIRE SQUID

Drawing of a vampire squid
Carl Chun, Wikimedia Commons // Public Domain

This deep-sea critter isn’t a squid. It’s the only surviving member of a scientific order that has characteristics of both octopuses and squids. And don’t let the word “vampire” scare you; it only eats bits of falling marine debris (dead stuff, poop, and so on), and it’s only about 11 inches long.

13. MALE FERN & LADY FERN

Early botanists thought that these two ferns belonged to the same species. They figured that the male fern was the male of the species because of its coarse appearance. The lady fern, on the other hand, has lacy fronds and seemed more ladylike. Gender stereotypes aside, male and lady Ferns belong to entirely separate species, and almost all ferns can make both male and female reproductive cells. If ferns start looking manly or womanly to you, maybe you should take a break from botany.

14. TENNESSEE WARBLER

You will never find a single Tennessee warbler nest in Tennessee. This bird breeds mostly in Canada, and spends the winter in Mexico and more southern places. But early ornithologist Alexander Wilson shot one in 1811 in Tennessee during its migration, and the name stuck.

15. CANADA THISTLE

Though it’s found across much of Canada, this spiky plant comes from Europe and Asia. Early European settlers brought Canada thistle seeds to the New World, possibly as accidental hitchhikers in grain shipments. A tough weed, the plant soon spread across the continent, taking root in fields and pushing aside crops. So why does it have this inaccurate name? Americans may have been looking for someone to blame for this plant—so they blamed Canada.

A version of this story originally ran in 2015.

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18 Tea Infusers to Make Teatime More Exciting
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Make steeping tea more fun with these quirky tea infusers.

Mental Floss has affiliate relationships with certain retailers and may receive a small percentage of any sale. But we only get commission on items you buy and don’t return, so we’re only happy if you’re happy. Thanks for helping us pay the bills!

1. SOAKING IT UP; $7.49

man-shaped tea infuser
Amazon

That mug of hot water might eventually be a drink for you, but first it’s a hot bath for your new friend, who has special pants filled with tea.

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2. A FLYING TEA BOX; $25.98

There’s no superlaser on this Death Star, just tea.

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3. SPACE STATION; $9.99

astronaut tea infuser
ThinkGeek

This astronaut's mission? Orbit the rim of your mug until you're ready to pull the space station diffuser out.

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4. BE REFINED; $12.99

This pipe works best with Earl Grey.

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5. A RIBBITING OPTION; $10.93

This frog hangs on to the side of your mug with a retractable tongue. When the tea is ready, you can put him back on his lily pad.

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6. ‘TEA’ ALL LIVE IN A YELLOW SUBMARINE; $5.95

It’s just like the movie, only with tea instead of Beatles.

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7. SHARK ATTACK; $6.99

shark tea infuser
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This fearsome shark patrols the bottom of your mug waiting for prey. For extra fun, use red tea to look like the end of a feeding frenzy.

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8. PERFECT FOR A RAINY DAY; $12.40

This umbrella’s handle conveniently hooks to the side of your mug.

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9. AN EGGCELLENT INFUSER; $5.75

cracked egg tea infuser
Amazon

Sometimes infusers are called tea eggs, and this one takes the term to a new, literal level.

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10. FOR SQUIRRELY DRINKERS; $8.95

If you’re all right with a rodent dunking its tail into your drink, this is the infuser for you.

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11. HANGING OUT; $12.85

This pug is happy to hang onto your mug and keep you company while you wait for the tea to be ready.

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12. ANOTHER SHARK OPTION; $5.99

If you thought letting that other shark infuser swim around in the deep water of your glass was too scary, this one perches on the edge, too busy chomping on your mug to worry about humans.

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13. RUBBER DUCKIE, YOU’RE THE ONE; $8.95

Let this rubber duckie peacefully float in your cup and make teatime lots of fun.

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14. DIVING DEEP; $8.25

This old-timey deep-sea diver comes with an oxygen tank that you can use to pull it out.

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15. MAKE SWEET TEA; $10

This lollipop won't actually make your tea any sweeter, but you can always add some sugar after.

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16. A SEASONAL FAVORITE; $7.67

When Santa comes, give him some tea to go with the cookies.

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17. FLORAL TEA; $14.99

Liven up any cup of tea with this charming flower. When you’re done, you can pop it right back into its pot.

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18. KEEP IT TRADITIONAL; $7.97

If you’re nostalgic for the regular kind of tea bag, you can get reusable silicon ones that look almost the same.

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