Tag Archives: starfish

Episode 359: The Antarctic Death Star(fish)!

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Thanks to Morgan for suggesting this week’s topic, the Antarctic Death Star!

Further reading:

Giant Monster Starfish ALERT

Echinoderm Tube Feet Don’t Suck! They Stick!

Bodies of Starfish and Other Echinoderms Are Really Just Heads, New Research Suggests

The Antarctic death star [from first link listed above]:

The “beartrap” structures, magnified [from first link listed above]:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

It’s been way too long since we talked about an invertebrate, so this week we’ll look at one suggested by Morgan, the Antarctic death star.

It has a lot of other names too, including the Antarctic sun starfish and the wolftrap or beartrap starfish. Its scientific name is Labidiaster annulatus. I’m going to call it the death star because I think that’s hilarious.

As you may have guessed from its common names, the Antarctic death star is a starfish that lives in cold ocean waters near the Antarctic, AKA the south pole. But its common names also hint at how it gets its food, and this would be a good time to take a moment and be glad you’re not a copepod that also lives in the Antarctic Ocean.

The death star is reddish-brown on its dorsal side, white underneath. It’s a large starfish, up to two feet across, or 60 cm, and it also has a lot of legs, more properly called rays—up to 50 of them. The rays are long, narrow, and very flexible, and the undersides have rows of little structures called tube feet. All echinoderms, including starfish, have these tube feet and they’re used for several purposes. One important purpose is helping the animal stick to a hard surface, which allows it to climb around more easily and right itself if it gets flipped over.

For over 150 years scientists thought the tube feet acted like little suction cups, but that didn’t explain how a starfish or other echinoderm could stick to porous surfaces. It wasn’t until 2012 that a study was published explaining how the tube feet actually work. The tube feet exude tiny amounts of a sticky chemical that acts like glue.

The death star’s body also has little spines and bumps all over it, but it also has some structures that give the animal its other names, the wolftrap or beartrap starfish. The structures are called pedicellariae [PED-uh-suh-LAIR-ee-aye], which are also common in echinoderms. Most echinoderms seem to use them to keep algae and other organisms from settling on the body, although scientists aren’t completely sure. Pedicellariae have muscles and sensory receptors, and when something touches them, they snap shut like a trap. In the case of the Antarctic death star, its pedicellariae are extra big and really sharp. When a krill or other tiny animal brushes against one of these little traps, it grabs the animal and then the death star can eat it.

But that’s just part of what’s going on when the death star goes hunting, so let’s discuss it in more detail.

Most starfish spend almost all their time on the ocean floor, walking around looking for food. The death star does this too, but not all the time. Quite often a death star will climb on top of a rock or other large structure, and then it will extend some of its rays up and out into the water. It waves its rays around and if it touches a small animal, it will wrap the rays around it. The pedicellariae also snap shut. Then the death star can eat whatever it caught. Usually this is krill or amphipods, but it’s not a picky eater. Since it will eat animals it finds already dead, researchers aren’t completely sure if the death star ever catches fish. They’ve certainly found dead fish in death star stomachs, but the water it lives in is so cold that not many fish live there anyway. Fish don’t make up a big part of the death star’s diet, whether or not it’s catching them itself. The death star also eats other starfish, including smaller death stars.

Like other starfish, the death star can eat surprisingly large pieces of food because it can evert its stomach. This means it can actually push its stomach out through its mouth and engulf whatever large food it’s found or caught. The digestion process starts right away, which allows the starfish to eat food that can’t actually fit through its mouth. It doesn’t chew its food because it doesn’t have any kind of teeth or jaws, but who needs teeth and jaws if your stomach can just reach out and grab food?

While I was researching the death star, I came across a study published in November 2023 about echinoderms, so let’s learn something surprising about starfish and their relations in general.

Echinoderms demonstrate radial symmetry instead of bilateral symmetry. That’s why you can’t tell when a starfish or other echinoderm is facing forward, because it doesn’t actually have a forward. But it’s actually more complicated than it sounds, because the distant ancestor of echinoderms, which lived during the Cambrian almost half a billion years ago, did demonstrate bilateral symmetry, and the larvae of modern echinoderms do too. When a modern echinoderm larva develops into an adult, the left side of its body is the only part that grows. The right side of its body is absorbed and from then on the body develops radially. It actually shows pentaradial symmetry, with five sections around the central part of the body. That’s why so many starfish have five rays, although obviously not all of them. The death star starts out with five rays but adds more and more as it grows.

For a long time scientists have wondered if echinoderms technically have heads or if they’re just bodies. They don’t have eyes or nostrils or most other body parts that we associate with the head, just an oral opening in the middle of the underside of the disc. Starfish do have cells at the ends of their rays that act as eyespots, which are sensitive to light and dark but can’t actually see anything else. Instead of a brain, it has a nerve ring around its mouth and connected nerve nets in its rays, and its digestive system extends into its rays.

In other words, it sure seems like an echinoderm has no head and is basically just a weird body. But the new study came to a surprising conclusion. The study examined starfish genetics and discovered that the genes associated with head development were there. It was the genes associated with the development of a body and tail that were missing. In other words, the starfish, and echinoderms in general, are just really complicated heads.

You can find Strange Animals Podcast at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon at patreon.com/strangeanimalspodcast if you’d like to support us for as little as one dollar a month and get monthly bonus episodes.

Thanks for listening!

Episode 135: Smallest of the Large

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This week we’re looking at some very small animals–but not animals that we think of as small. Join us for a horrendously cute episode!

Further reading:

The Echinoblog

Further listening:

Animals to the Max episode #75: The Sea Panda (vaquita)

Varmints! episode #49: Hippos

Further watching:

An adorable baby pygmy hippo

The Barbados threadsnake will protecc your fingertip:

Parvulastra will decorate your thumbnail:

Berthe’s mouse lemur will defend this twig:

The bumblebee bat will eat any bugs that come near your finger:

The vaquita, tiny critically endangered porpoise:

The long-tailed planigale is going to steal this ring and wear it as a belt:

He höwl:

A pygmy hippo and its mother will sample this grass:

This Virgin Islands dwarf gecko will spend this dime if it can just pick it up:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

I talk a lot about biggest animals on this podcast, so maybe it’s time to look at the very smallest animals. I don’t mean algae or bacteria or things like that, I mean the smallest species of animals that aren’t usually considered especially small.

We’ll start with the smolest snek, the Barbados threadsnake. It only lives on a few islands in the Caribbean, notably Barbados. The very largest individual ever measured was only 4.09 inches long, or 10.4 cm, but most are under four inches long. But it’s an extremely thin snake, not much thicker than a spaghetti noodle.

The Barbados threadsnake mostly eats termites and ant larvae. It spends most of its time in leaf litter or under rocks, hunting for food. The female only lays one single egg, but the baby is relatively large, about half the mother’s length when it hatches.

That’s so cute. Why are small things so cute?

Remember the starfish episode where we talked about the largest starfish? Well, what’s the smallest starfish? That would be Parvulastra parvivipara, which is smaller than a fingernail decoration sticker. It grows to about ten millimeters across and is orangey-yellow in color. It lives on the coast of Tasmania in rock pools between low and high tide, called intertidal rock pools.

If you remember the Mangrove killifish from a few episodes ago, you’ll remember how killifish females are hermaphrodites that produce both eggs and sperm, and usually self-fertilize their eggs to produce tiny clones of themselves. Well, Parvulastra does that too, although like the killifish it probably doesn’t always self-fertilize its eggs. But then it does something interesting for a starfish. Instead of releasing its eggs into the water to develop by themselves, Parvulastra keeps the eggs inside its body. And instead of the eggs hatching into larvae, they hatch into impossibly tiny miniature baby starfish, which the parent keeps inside its body until the baby is big enough to survive safely on its own.

But what do the baby starfish eat while they’re still inside the mother? Well, they eat their SIBLINGS. The larger babies eat the smaller ones, and eventually leave through one of the openings in the parent’s body wall, called gonopores. Researchers theorize that one of the reasons the babies leave the parent is to escape being eaten by its siblings. And yes, occasionally a baby grows so big that it won’t fit through the gonopores. So it just goes on living inside the parent.

Next, let’s look at the smallest primate. The primate order includes humans, apes, monkeys, and a lot of other animals, including lemurs. And the very smallest one is Berthe’s mouse lemur. Its body is only 3.6 inches long on average, or 9.2 cm, with a tail that more than doubles its length. Its fur is yellowish and brownish-red.

Berthe’s mouse lemur was only discovered in 1992. It lives in one tiny area of western Madagascar, where it lives in trees, which means it’s vulnerable to the deforestation going on all over Madagascar and is considered endangered.

It mostly eats insects, but also fruit, flowers, and small animals of various kinds. Its habitat overlaps with another small primate, the gray mouse lemur, but they avoid each other. Madagascar has 24 known mouse lemur species and they all seem to get along well by avoiding each other and eating slightly different diets. Researchers discover new species all the time, including three in 2016.

Last October we had an episode about bats, specifically macrobats that have wingspans as broad as eagles’. But the smallest bat is called the bumblebee bat. It’s also called Kitti’s hog-nosed bat, but bumblebee bat is way cuter. It’s a microbat that lives in western Thailand and southeast Myanmar, and like other microbats it uses echolocation to find and catch flying insects. Its body is only about an inch long, or maybe 30 millimeters, although it has a respectable wingspan of about 6 ½ inches, or 17 cm. It’s reddish-brown in color with a little pig-like snoot, and it only weighs two grams. That’s just a tad more than a single Pringle chip weighs.

Because the bumblebee bat is so rare and lives in such remote areas, we don’t know a whole lot about it. It was only discovered in 1974 and is increasingly endangered due to habitat loss, since it’s only been found in 35 caves in Thailand and 8 in Myanmar, and those are often disturbed by people entering them. The land around the caves is burned every year to clear brush for farming, which affects the bats too.

The bumblebee bat roosts in caves during the day and most of the night, only flying out at dawn and dusk to catch insects. It rarely flies more than about a kilometer from its cave, or a little over half a mile, but it does migrate from one cave to another seasonally. Females give birth to one tiny baby a year. Oh my gosh, tiny baby bats.

So what about whales and dolphins? You know, some of the biggest animals in Earth’s history? Well, the vaquita is a species of porpoise that lives in the Gulf of California, and it only grows about four and a half feet long, or 1.4 meters. Like other porpoises, it uses echolocation to navigate and catch its prey. It eats small fish, squid, crustaceans, and other small animals.

The vaquita is usually solitary and spends very little time at the surface of the water, so it’s hard to spot and not a lot is known about it. It mostly lives in shallow water and it especially likes lagoons with murky water, properly called turbid water, since it attracts more small animals.

Unfortunately, the vaquita is critically endangered, mostly because it often gets trapped in illegal gillnets and drowns. The gillnets are set to catch a different critically endangered animal, a fish called the totoaba. The totoaba is larger than the vaquita and is caught for its swim bladder, which is considered a delicacy in China and is exported on the black market. The vaquita’s total population may be no more than ten animals at this point, fifteen at the most, and the illegal gillnets are still drowning them, so it may be extinct within a few years. A captive breeding plan was tried in 2017, but porpoises don’t do well in captivity and the individuals the group caught all died. Hope isn’t lost, though, because vaquita females are still having healthy babies, and there are conservation groups patrolling the part of the Gulf of California where they live to remove gill nets and chase off fishing boats trying to set more of the nets.

If you want to learn a little more about the vaquita and how to help it, episode 75 of Corbin Maxey’s excellent podcast Animals to the Max is an interview with a vaquita expert. I’ll put a link in the show notes.

Next, let’s talk about an animal that is not in danger of extinction. Please! The long-tailed planigale is doing just fine, a common marsupial from Australia. So, if it’s a marsupial, it must be pretty big—like kangaroos and wallabies. Right? Nope, the long-tailed planigale is the size of a mouse, which it somewhat resembles. It even has a long tail that’s bare of fur. It grows to 2 ½ inches long not counting its tail, or 6.5 cm. It’s brown with longer hind legs than forelegs so it often sits up like a tiny squirrel. Its nose is pointed and it has little round mouse-like ears. But it has a weird skull.

The long-tailed planigale’s skull is flattened—in fact, it’s no more than 4 mm top to bottom. This helps it squeeze into cracks in the dry ground, where it hunts insects and other small animals, and hides from predators.

The pygmy hippopotamus is a real animal, which I did not know until recently. It grows about half the height of the common hippo and only weighs about a quarter as much. It’s just over three feet tall at the shoulder, or 100 cm. It’s black or brown in color and spends most of its time in shallow water, usually rivers. It’s sometimes seen resting in burrows along river banks, but no one’s sure if it digs these burrows or makes use of burrows dug by other animals. It comes out of the water at night to find food. Its nostrils and eyes are smaller than the common hippo’s.

Unlike the common hippo, the pygmy hippo lives in deep forests and as a result, mostly eats ferns, fruit, and various leaves. Common hippos eat more grass and water plants. The pygmy hippo seems to be less aggressive than the common hippo, but it also shares some behaviors with its larger cousins. For instance, the pooping thing. If you haven’t listened to the Varmints! Episode about hippos, you owe it to yourself to do so because it’s hilarious. I’ll put a link in the show notes to that one too. While the hippo poops, it wags its little tail really fast to spread the poop out across a larger distance.

Also like the common hippo, the pygmy hippo secretes a reddish substance that looks like blood. It’s actually called hipposudoric acid, which researchers thinks acts as a sunscreen and an antiseptic. Hippos have delicate skin with almost no hair, so its skin dries out and cracks when it’s out of water too long.

The pygmy hippo is endangered in the wild due to habitat loss and poaching, but fortunately it breeds successfully in zoos and lives a long time, up to about 55 years in captivity. For some reason females are much more likely to be born in captivity, so when a male baby is born it’s a big deal for the captive breeding program. I’ll put a link in the show notes to a video where you can watch a baby pygmy hippo named Sapo and his mother. He’s adorable.

Finally, let’s finish where we started, with another reptile. The smallest lizard is a gecko, although there are a lot of small geckos out there and it’s a toss-up which one is actually smallest on average. Let’s go with the Virgin Islands dwarf gecko, which lives on three of the British Virgin Islands. It’s closely related to the other contender for smallest reptile, the dwarf sphaero from Puerto Rico, which is a nearby island, but while that gecko is just a shade shorter on average, it’s much heavier.

The Virgin Islands dwarf gecko is only 18 mm long not counting its tail, and it weighs .15 grams. A paperclip weighs more than this gecko. It’s brown with darker speckles and a yellow stripe behind the eyes. Females are usually slightly larger than males. Like other geckos, it can lose its tail once and regrow a little stump of a tail.

The Virgin Islands dwarf gecko lives in dry forests and especially likes rocky hills, where it spends a lot of its time hunting for tiny animals under rocks. We don’t know a whole lot about it, but it does seem to be rare and only lives in a few places, so it’s considered endangered. In 2011 some rich guy decided he was going to release a bunch of lemurs from Madagascar onto Moskito Island, one of the islands where the dwarf gecko lives. Every conservationist ever told him oh NO you don’t, rich man, what is your problem? Those lemurs will destroy the island’s delicate ecosystem, drive the dwarf gecko and many other species to extinction, and then die because the habitat is all wrong for lemurs. So Mr. Rich Man said fine, whatever, I’ll take my lemurs and go home. And he did, and the dwarf gecko was saved.

Look, if you have so much money that you’re making plans to move lemurs halfway across the world because you think it’s a good idea, I can help take some of that money off your hands.

You can find Strange Animals Podcast online at strangeanimalspodcast.blubrry.net. That’s blueberry without any E’s. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. We also have a Patreon if you’d like to support us that way.

Thanks for listening!

Episode 079: Starfish and Friends

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This week’s episode is all about echinoderms, or at least the star-shaped echinoderms! Thanks to Llewelly for the suggestion about feather stars and crinoids!

A very pretty starfish:

Crown of thorns starfish. Do not touch:

Pumpkin starfish or orange throw pillow? YOU DECIDE:

Sea daisies. Not much to look at tbh:

A banded arm brittle star:

Ruby brittle stars:

Brittle stars riding around in a jelly:

A basket star:

Basket stars got TEETH THINGS:

A stemmed crinoid:

A lovely feather star:

Further reading:

Echinoblog, a really amazing resource and so much fun to browse

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week we’re going to look at some marine animals that most people barely think about, but which are really interesting. It was going to just be about starfish and maybe one other animal, but while I was still researching starfish, listener Llewelly suggested I cover feather stars and crinoids. They’re related to starfish, so I thought I’d tack them on. And if you talk about starfish, you really have to talk about brittle stars too, and if you talk about brittle stars you have to talk about basket stars. Basically, I had to stop myself from breaking this episode into two big episodes about echinoderms. It’s just the stars this time.

Before we get into echinoderms, though, a quick note about my schedule. Next week I’m going on a trip to Paris, France! I know it sounds like I’m rich and just travel as my whim takes me, but actually I just have really generous relatives. A week and a half after I return from Paris, I’ll be in Atlanta, Georgia for DragonCon, where I’ll be on a panel about podcasting. In other words, I won’t be around much on social media for the rest of August, but don’t worry, I’ll have episodes recorded and scheduled to run normally while I’m gone.

Okay, now let’s get into echinoderms. Echinoderms include sand dollars, sea urchins, starfish, and many others, and every single echinoderm lives in the ocean. Many of them can regenerate limbs and other body parts, and instead of blood they have a water vascular system. In most echinoderms, seawater enters the body through slits or pores, then travels through canals within the body to transport oxygen to cells and waste products out of cells. Echinoderms have internal skeletons made of calcium carbonate, but they’re invertebrates because they don’t have a backbone. Heck, technically they don’t even have a back.

Echinoderms show radial symmetry, which means their bodies are roughly the same in all directions instead of having a clear front and rear. The echinoderms we’re talking about this week are ones that also exhibit pentaradial symmetry, which means they have five sides. And the best-known echinoderms out there are starfish. There are about 1,500 species of starfish known, and some of them are really weird and some are only kind of weird. Most have five arms but some have a whole lot more.

Starfish are members of the class Asteroidea, which just delights me. A better name for them is sea star, since they’re not fish at all. Starfish have been around for at least 450 million years, but in 2012 paleontologists found a fossil of the oldest known ancestor of starfish in the mountains of Morocco. It’s about 515 million years old, from the Cambrian period. It was only about an inch and a half long, or 4 cm, and looked similar to the modern-day sea lily, or crinoid. If you recall, the Cambrian period was when life was expanding rapidly in the oceans and evolving sometimes quite strange body plans. You know, like things with FIVE LEGS.

Most starfish have ossicles in their skin, little hard beads of calcium carbonate that help protect the animal. In some starfish, the ossicles are more like spines or even spikes. Although cartoons of starfish usually make them look like their legs are always exactly star-shaped, the legs are actually quite flexible. If a starfish is flipped upside down, it bends a couple of its legs down to flip itself back over.

The starfish’s mouth is in the very center of its body, the part in the middle of the legs, known as the disc. Different starfish use their mouths differently. That sounds confusing, but just hang on, because things are about to get weird and gross.

Starfish are primarily predators. Some starfish just swallow their prey whole and digest it in the stomach. Pretty normal. But other starfish—look, I don’t know how to tell you this, so I’ll just say it. They turn their stomach inside out, called eversion, squish it around the prey, and start the digestive process. Part of the stomach stays inside the body, and when the prey has been digested enough that’s it sort of a lumpy soup, the starfish retracts its everted stomach and the food back into the body. This means that the starfish can eat prey that’s bigger than it is.

A lot of starfish eat bivalves of various kinds, like clams. Say a starfish finds a clam and wants to eat it. The clam is closed up tight and starfish don’t have teeth or claws to break the clam open. But starfish do have tiny tubes on the bottoms of their legs, called tube feet. These tubes act like suction cups, although they actually stick to things with a chemical reaction. So the starfish latches onto both shells of the bivalve with its tube feet and pulls. It probably isn’t strong enough to pull the clam open completely, but it doesn’t need to. It just needs a little space so it can evert its stomach and squish it into the clam’s shell. Then it releases digestive enzymes and the clam is doomed.

Starfish can’t move very fast, and lots of animals eat them. But they can regenerate lost legs if some of them are bitten off. The starfish doesn’t have a brain, although it does have a nerve net. Plus, it has sensory bundles at the ends of its arms that can detect smells, along with eye spots at the end of each leg. The eye spots basically just detect light and darkness and they don’t actually look like eyes, which is a good thing because that would be terrifying.

Starfish arms, or legs, are properly called rays. I will continue to confuse everyone by calling them arms or legs depending on which word sounds better to me at the time.

So let’s get down to the nitty-gritty. What is the biggest starfish? What is the weirdest starfish? Could a starfish actually kill you, and I don’t mean by making you faint with terror and drown, which is what would happen to me if I accidentally touched one.

Let’s start with the biggest starfish. Starfish don’t actually get all that enormous. Even the biggest ones are typically only about two feet across, or 60 cm. The sunflower star can grow more than three feet across, or over a meter, and can weigh up to 11 pounds, or 5 kilograms. AND it has a ridiculous number of arms, up to 24 of them.

Sunflower stars can be purple, red, pink, brown, orange, yellow, or even white. They live on the sea bed along the Pacific coast, usually where it’s shallow but sometimes nearly 1500 feet deep, or over 450 meters. Young sunflower stars only have five arms, but as they get older they grow more arms. One genus of starfish, commonly called Heliaster, looks similar to the sunflower star even though it’s not that closely related to it, but some individuals can have up to 50 legs.

Recently, a bed of 350 fossil starfish were found in Florida, so well preserved that paleontologists were able to identify them as Heliaster michrobachius, which is still around today. But it lives off the western coast of Central and South America, from Mexico all the way down to Chile—but it’s not found anywhere else. So what were they doing in Florida three million years ago?

Remember the Great American Interchange, where the isthmus of Panama formed, connecting North and South America and allowing animals from both places to spread into the other continents? Before then, North America was separate from South America, so Heliaster undoubtedly lived along North America’s southern coast. After the isthmus formed, currents, salinity, and many other factors changed, which probably led to Heliaster dying out in the Atlantic side of the continent. Fortunately, it survived in the Pacific side.

So, what is the weirdest starfish? It’s really hard to decide. All starfish are weird, frankly. Labidiaster annulatus can grow up to two feet across, or 60 cm, and has 40 to 45 long, thin legs with sharp spines that can actually grab prey. The starfish holds its legs out and wriggles them like fishing lines, and when a little fish or an amphipod comes close, the spines snag it. The starfish wraps its arms around the prey and pulls it to its mouth, where it everts its stomach and starts digesting.

The crown-of-thorns starfish mostly eats coral polyps and is covered with thorny spines that are venomous. It can have up to 21 arms and is the same size as Labidiaster, but with a thicker body and much shorter legs. It looks scary, but it’s actually delicate and rarely survives being lifted out of the water for even a short time. It lives in a lot of areas, including part of the Pacific Ocean, Red Sea, and along the east African coast, but it’s most common around Australia. At one point people worried that it was killing a lot of the coral in Australia’s great barrier reef, but under ordinary circumstances it actually helps maintain biodiversity in coral reefs by preying mainly on fast-growing coral. This allows slow-growing coral to flourish. Every so often, though, there’s a population boom among the crown-of-thorns starfish. Researchers aren’t sure why, and when it happens Australia has tried various population control measures to keep their numbers down and protect the reefs.

The pumpkin sea star is fat, thick, and orange. It’s big too, literally the size of a pumpkin. It’s also rare, and was only discovered in 1997. Even though it’s big, its skeleton is very small and it’s basically very meaty, which makes it look like a star-shaped orange throw pillow. Now I want a pumpkin starfish throw pillow. It lives in the Indo-Pacific up to about 650 feet deep, or 200 meters, but not much is known about it yet.

Luidia maculata has long, flattened arms that are brown and black striped above and white underneath, sometimes with a brown daisy pattern on its body disc. Seriously, who knew these things were so pretty? It lives in shallow water in the Indo-Pacific and often buries itself in the sand with the help of the long spines on the undersides of its legs. It doesn’t have an eversible stomach so it just swallows its prey whole, including sand dollars, sea urchins, clams, other starfish, sea cucumbers, and snails. Whatever’s left over after it has digested its prey, it spits out.

The sea daisy is a deep-sea animal described in 1986 after being discovered by accident. A team collecting samples of wood from the South Pacific seabed found nine of the strange creatures and didn’t know what they were. It’s small, only about 9 mm long, and is shaped roughly like an umbrella without a handle. Its upper surface is covered with plates with spines along the edges, and underneath it has a single row of tube feet and a membrane. Researchers at first decided the sea daisy was so different from other echinoderms that it needed its own class, but further study determined that it’s actually a type of starfish even though it has no arms and no stomach. In fact, it most closely resembles a juvenile starfish, but where starfish grow arms as they develop, the sea daisy never grows arms and instead grows outward along its circumference, like a wheel. It lives among wood that has sunk to the bottom of the ocean to a depth of at least 3300 feet, or 1,000 meters, and researchers think it may eat bacteria that grow on the wood. The membrane on its underside resembles an everted stomach.

Okay, one more. A starfish sometimes referred to as a slime star is covered with a soft, squishy, gelatinous surface. Its body is frequently almost transparent too. It usually lives in the deep sea, with new species found just about every time a deep-sea expedition scouts around on the sea floor. The largest are almost a foot across, or nearly 30 cm. Since they’re so delicate, it’s hard to study them, so not a lot is known about them. But there is a shallow-living species that has been studied a little more, and we know one important thing about them. If you pick up a slime star, it will secrete just ridiculous amounts of slime. This helps it keep from being eaten. The slime may also contain a soap-like toxin.

That brings us to our last question about starfish: can starfish kill you? No. No, they can’t. Even the crown-of-thorns starfish venom won’t kill you, just hurt like crazy for a few hours or as much as a week. The venom actually chemically resembles soap or detergent so isn’t very toxic to humans or other animals, but it does make the starfish taste bad.

Next, let’s look at brittle stars. Brittle stars look superficially like starfish and are closely related to them. Their legs are usually very long and slender, with the legs of some species growing up to two feet long, or 60 cm. The legs are supported by a skeleton made of plates called vertebral ossicles, which resembles a bike chain.

Brittle stars have five arms and a round central disc, with the legs much more differentiated from the disc than starfish legs are. They mostly scavenge for bits of food or eat worms and other small animals. They usually move slowly, but when they need to, they can really zoom around quickly. Their legs are extremely flexible and they can use them for swimming or crawling. Sometimes a brittle star will raise its body disc up and walk on its legs sort of like a spider, which is oddly creepy but also remarkably adorable. Look, I don’t mind telling you, I really like brittle stars. I barely knew what they were before I started researching them, but now I think they’re one of the best things ever.

Some brittle stars are bioluminescent, but only along their arms. Most species can regenerate their arms like starfish can, but not as well as starfish, and some species can’t regenerate at all.

Brittle stars are more freewheeling than their starfish cousins. For instance, one brittle star, Ophiocnemis marmorata, hitches rides on jellyfish. One 2017 study found that 79% of moon jellies examined hosted brittle stars, some riding inside the jellys’ bells, some riding in the tentacles near the oral arms. Larger jellies carry more brittle stars, while small ones usually only have a few. It turns out that the brittle stars steal food from the jellies, known as kleptoparasitism. They also gain some protection from living inside a jelly, and they get a free ride to new parts of the ocean. Researchers hypothesize that the brittle stars find their jelly hosts as larvae, ride around with it for a while, and drop off to live on the sea floor. Since the brittle star prefers tropical waters, it abandons its host jelly when it migrates into colder water.

Brittle stars are divided into two groups, brittle stars and basket stars. Brittle stars live all over and are especially common around coral reefs, but basket stars mostly live in deep water. While brittle stars have relatively simple, snakey arms, basket star arms are long and branched. Sometimes the branches of their arms are so elaborate, they look more like a kind of coral or like a tumbleweed sitting on the bottom of the ocean.

The biggest basket star we know of is probably Gorgonocephalus. There are at least ten species, and they can be hard to tell apart even by experts. Gorgonocephalus’s body disc can grow some 5 ½ inches across, or 14 cm, but its five net-like arms can grow over two feet long, or 70 cm. It’s white or yellowish in color, and its disc is often dark brown. During the day it hides among sponges and corals, but at night it comes out to hunt.

Basket stars mostly eat small animals like krill, jellyfish, and copepods that get tangled in their elaborately branched arms. The arms have hooks and spines all over them too. Basket stars will sit on a rock or a sponge or something similar, and extend their arms as though casting a net. When an animal strays into the net, the basket star carries it to the mouth on the underside of its body disc. And the mouth is full of spikes. Like many deep-sea animals, we don’t know a whole lot about basket stars and new species are discovered pretty frequently.

The last star we’ll look at this time is the feather star, but to learn about the feather star we also have to learn about the crinoid. If you’ve taken a geology class, you probably remember crinoid stem fossils. They’re incredibly common fossils, because crinoids used to be incredibly common animals. Pieces of crinoid stem fossils are sometimes called St. Cuthbert’s beads, and they’ve been used by humans to make jewelry for millennia.

In the past crinoids had five arms, but at some point each arm developed into two, so many modern crinoids have ten arms. In addition, some species have arms that branch. The arms have feathery appendages and tube feet coated with mucus, which helps trap tiny bits of food. Crinoids’ water vascular system is internal, unlike in starfish and brittle stars, which pump water in from outside.

Crinoids with stalks look like plants and are often called sea lilies. Some even have tiny rootlike filaments that help it attach to the sea floor or to rocks or other structures. The stem is slender with the cup-like body disc, called a calyx, and feathery arms at the top. Many species of crinoid have stems as juveniles, but become free-swimming when they reach maturity. Today some deep-sea crinoids can have stems a little over three feet long, or roughly a meter, but one fossil crinoid found had a stem 130 feet long, or 40 meters. But unlike true plants, crinoids can uproot themselves and move to a better location.

Most crinoids today are free-swimming, and these are the feather stars. They may have a vestigial stalk or may have no stalk at all. Most feather stars are sedentary, only crawling around for short distances, but some can swim with their arms. Many are brightly colored and absolutely beautiful.

I could keep talking about echinoderms for hours, but this episode is already getting long. Eventually I’ll do a follow-up episode about other echinoderms, like sea urchins. Until then, if you want to learn more about echinoderms I highly recommend a site called Echinoblog. It’s run by Dr. Chris Mah, a starfish expert, whose enthusiastic and informative posts about echinoderms really helped me learn to appreciate them. I’ll put a link in the show notes. Usually, the more I look at pictures of invertebrates, the more gross they seem, but the opposite is true for feather stars and brittle stars. They’re just gorgeous. Starfish, on the other hand, I would rather admire from afar.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or whatever platform you listen on. We also have a Patreon if you’d like to support us that way.

Thanks for listening!

Episode 054: Regenerating Animals

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This week we’re going to learn about animals that can regenerate parts of their body. What animals can do it, how does it work, and can humans figure out how to make it work for us too?

Thanks to Maxwell of the awesome Relic: The Lost Treasure podcast for suggesting this week’s topic!

The planarian, not exciting to look at but you can get a lot of them easily:

A starfish leg growing a new starfish, or possibly a slightly gross magic wand. Ping! You’ve been turned into a magical starfish:

The adorable axolotl:

The almost as adorable African spiny mouse:

A hydra. Not really very adorable except possibly to other hydras but kind of pretty:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

This week’s episode was going to be about lungfish, but I had to postpone it because I ran across some conflicting information about a mystery lungfish, which required me to order a book that probably won’t arrive for a week or two. So when I tweeted about needing a new topic quick, Maxwell of the Relic: The Lost Treasure podcast suggested animals that can regenerate parts of their bodies.

We’ve touched on regenerative abilities before in one or two episodes. Some lizards can drop their tail if threatened, which then regrows later—but a lizard can only do that once. The fish-scaled gecko from episode 20 can lose its scales and regenerate them repeatedly. But other animals can regenerate not just bits and pieces, but entire organs and even their brains. The sea lamprey can even regenerate spinal cord cells. You better believe researchers are trying to figure out how regeneration works and if it can be adapted for human application.

A lot of worms can regenerate lost pieces, including earthworms. Whenever I’m gardening and accidentally cut an earthworm in half with the shovel, I reassure myself that the worm will regenerate the end I cut off. Some species can even grow back from both cut pieces, effectively turning one earthworm into two, depending on where it is severed, although that’s rare. Some species of worm can only regrow the tail, but some can regrow the head. And some, of course, can’t regrow anything. Leeches are a type of worm but they can’t regenerate at all.

Planarians are flatworms. Some species live in water, some in damp areas on land, but they can all regenerate. If you cut a planarian in two, each half will regenerate into a new planarian. If you cut a planarian in three, you’ll get three planarians. Cut one into four, you get four planarians, and so on and on. Researchers with a lot of time and patience have determined that you can cut a planarian into as many as 277 pieces and you will get 277 planarians after a few weeks. But I guess if you cut a planarian into 278 or more pieces, some of the extra pieces won’t do anything.

Starfish are well-known to regenerate lost or injured legs, and may even drop a leg to escape from predators the way some lizards drop their tails. Some species of starfish can regrow an entire starfish from a single limb. That’s oddly creepy. I don’t know why I find it so creepy. I don’t find the planarians creepy. It’s like if I was run over by a motorboat that chopped my arms and legs off, and instead of dying I not only regrew my arms and legs, my severed arms and legs each grew a new me. I don’t think I’d like that. Although I’m not going to get in the water so I doubt I’ll be run over by a motorboat, and also if I was, sharks would probably eat me before we could see if any parts regrew.

Many starfish relations, such as sea urchins and sea cucumbers, can also regenerate body parts. When the sea cucumber is threatened, it can and will eject its internal organs. They’re sticky and full of toxins, which deters predators, and the sea cucumber just regenerates them.

Most crustaceans, such as crabs and krill, can regenerate legs. So can spiders, which may drop legs to escape from predators. That’s called autotomy, by the way, when an animal detaches a body part to escape from a predator. Spiders molt their exoskeletons every so often as they grow, and lost limbs grow back after molting. Sometimes it takes a few molts for the leg to be the same size as the other legs. Spiders can also regenerate other lost or damaged parts, including mouthparts and spinnerets.

Salamanders and newts can regenerate limbs, tail, some organs, jaws, even parts of their eyes. Frogs and other amphibians can’t. Likewise, some fish can regenerate injured tissue, such as the zebrafish which can regrow fins and eye retinas, and some species of sharks that can regenerate skin tissue, while others can’t. The axolotl, which is an adorable rare salamander found in Mexico, can regrow just about any part of its body, including its spinal cord and up to half of its brain.

So what about mammals? Do any mammals have regenerative capabilities? As a matter of fact, yes. The African spiny mouse is the big regenerator among mammals. It’s actually more closely related to gerbils, and it has stiff guard hairs all over its body that stick out and make it look fuzzy but which act as spines to help ward off predators. But if a predator attacks anyway, three species of the spiny mouse can autotomically drop off part of its skin, which later grows back. Some species of spiny mouse are kept as pets, even though they don’t do very well in captivity. The pet species don’t have regeneration abilities, incidentally. However, they do have delicate tails that are easily injured, which they then lose, and the tail does not grow back.

Those three species of African spiny mouse can also regenerate ear tissue. If a spiny mouse’s ear is damaged, even if it has a hole as big as four mm across, it can regenerate the ear as good as new rather than heal it with scar tissue. A number of mammals can regenerate small injuries to ear cartilage under the right circumstances, including cats. Rabbits can also regrow damaged ear tissue, and have some other regenerative abilities too.

It’s all well and good to point out that a whole lot of animals can regenerate lost or damaged body parts. But how does it work? And more to the point, why can’t humans do it?

Technically, humans and other animals are regenerating certain cells all the time, especially skin cells and blood cells. Small cuts and scrapes heal up without scarring and we don’t think about it at all. Fingertips will grow back after injury and the liver can regenerate. The endometrium, which is the lining of the uterus, is partially reabsorbed into the body and partially expelled from the body every month during menstruation, then regrows. Toenails and fingernails regrow after injury. We just don’t think about all these things because they seem normal to us, whereas we can’t regrow a whole finger if it’s been chopped off, for instance.

I won’t go too deeply into how regeneration works, mostly because it’s complicated and I don’t want to screw it up too badly. There are also different types of regenerative abilities with different processes. Basically, though, as an example, when a salamander loses a leg, the cells surrounding the wound dedifferentiate, basically turning from regular skin cells or what have you into stem cells that can grow into anything the body needs. These cells form what’s called a blastema, which is just the fancy name for a bundle of dedifferentiated cells. Then the blastemal cells start differentiating again, this time into the cells needed to regrow the leg, just as stem cells grew legs when the salamander was developing in its egg.

It sounds pretty simple, put like that. I mean, that’s how we all develop in the first place, from a fertilized egg into a person who can make podcasts and eat cupcakes. The main problem is figuring out how to get human cells to dedifferentiate into a blastema. Because it’s not just injuries that could be helped if scientists figure this out, it’s all sorts of problems. People who have lost their sight due to retinal diseases could regrow new retinas. People born with birth defects could have the nonstandard parts regrown so that they work the way they’re supposed to.

Researchers are working hard to figure all this out. Stem cell research is a big part of regenerative research. Unfortunately, at some point the rumor started that all stem cells come from babies, specifically embryonic stem cells. When a human egg is fertilized, after a couple of days a blastocyst is formed from the cells, which is similar to a blastema but made of cells that have never differentiated into anything else. They’re brand new cells with the capacity to make a brand new human. Naturally, people are squiffy about taking cells that might make a baby and using them for something else. But amniotic fluid, the fluid that surrounds the baby as it’s growing in its mother, also contains stem cells, and they can be harvested without hurting the baby or the mother. You can also get stem cells from the umbilical cord right after a baby is born, and the umbilical cord is just cut off and thrown away anyway so you might as well give it a little extra use. But most stem cells used in research and treatment these days come from bone marrow, lipid cells in fat tissue, and blood, all of which can be extracted without harming the person. They’re not as powerful as embryonic and amniotic stem cells, but they have the benefit of being from the patient’s own body, so no immunosuppression is required to make sure the body accepts them in stem cell treatment.

That was a lot of confusing medical information, so let’s talk about one more animal that can regenerate, the hydra. We’ve talked about the hydra before in the jellyfish episode, which for a long time was our most popular episode. It’s now our second-most downloaded episode, with our first episode inexplicably in the top spot. The hydra is a freshwater animal related to jellies that can regenerate so completely it’s essentially immortal.

The hydra is related to the so-called immortal jellyfish we talked about in episode 19. It can regenerate just about any injury, and like the planarian it can regenerate into more than one copy of itself if it’s cut up into tiny pieces. It’s only a few millimeters long but its tiny body is full of stem cells, and as long as stem cells are present in the body part that was cut off, an entirely new hydra can grow from it. Because of its amazing regenerative abilities, some admittedly controversial studies suggest the hydra doesn’t age. That’s a neat trick, if you can manage it.

You can find Strange Animals Podcast online at strangeanimalspodcast.com. We’re on Twitter at strangebeasties and have a facebook page at facebook.com/strangeanimalspodcast. If you have questions, comments, or suggestions for future episodes, email us at strangeanimalspodcast@gmail.com. If you like the podcast and want to help us out, leave us a rating and review on Apple Podcasts or whatever platform you listen on. We also have a Patreon if you’d like to support us that way.

Thanks for listening!