Sign up for our mailing list! We also have t-shirts and mugs with our logo! Thanks to Nicholas and Emma for their suggestions this week as we learn about some (nearly) indestructible animals! Further listening: Patreon episode about Metal Animals (unlocked, no login required) Further reading: Even a car can't kill this beetle. Here's why The scaly-foot snail's shell is made of actual iron - and it's magnetic The scaly-foot gastropod (pictures from article linked above): The diabolical ironclad beetle is virtually unsquishable: Limpet shells: The business side of a limpet: Highly magnified limpet teeth: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week we’re going to learn about some indestructible animals, or at least animals that are incredibly tough. You may be surprised to learn that they’re all invertebrates. It’s a suggestion by Nicholas, and one of the animals Nicholas suggested was also suggested by Emma. We’ll start with that one, the scaly-foot gastropod, a deep-sea snail. We actually covered this one a few years ago but only in a Patreon episode. I went ahead and unlocked that episode so that anyone can listen to it, since I haven’t done that in a while, so the first part of this episode will sound familiar if you just listened to that one. The scaly-foot gastropod lives around three hydrothermal vents in the Indian Ocean, about 1 ¾ miles below the surface, or about 2,800 meters. The water around these vents, referred to as black smokers, can be more than 350 degrees Celsius. That’s 660 degrees F, if you even need to know that that’s too hot to live. The scaly-foot gastropod was discovered in 2001 but not formally described until 2015. The color of its shell varies from almost black to golden to white, depending on which population it’s from, and it grows to almost 2 inches long, or nearly 5 cm. It doesn’t have eyes, and while it does have a small mouth, it doesn’t use it for eating. Instead, the snail contains symbiotic bacteria in a gland in its esophagus. The bacteria convert toxic hydrogen sulfide from the water around the hydrothermal vents into energy the snail uses to live. It’s a process called chemosynthesis. In return, the bacteria get a safe place to live. The snail’s shell contains an outer layer made of iron sulfides. Not only that, the bottom of the snail’s foot is covered with sclerites, or spiky scales, that are also mineralized with iron sulfides. While the snail can’t pull itself entirely into its shell, if something attacks it, the bottom of its foot is heavily armored and its shell is similarly tough. Researchers are studying the scaly-foot gastropod’s shell to possibly make a similar composite material for protective gear and other items. The inner layer of the shell is made of a type of calcium carbonate, common in mollusk shells and some corals. The middle layer of the shell is regular snail shell material, organic periostracum, [perry-OSS-trickum] which helps dissipate heat as well as pressure from squeezing attacks, like from crab claws. And the outer layer, of course, is iron sulfides like pyrite and greigite. Oh, and since greigite is magnetic, the snails stick to magnets. Unfortunately, the scaly-foot gastropod is endangered due to deep-sea mining around its small, fragile habitat. Hopefully conservationists can get laws passed to protect the thermal vents and all the animals that live around them. The scaly-foot gastropod is the only animal known that incorporates iron sulfide into its skeleton or exoskeleton, although our next indestructible animal, the diabolical ironclad beetle, has iron in its name. The diabolical ironclad beetle lives in western North America, especially in dry areas. It grows up to an inch long, or 25 mm, and is a dull black or dark gray in color with bumps and ridges that make it look like a piece of tree bark. Since it lives on trees,