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Join us this week for some interesting crabs! Thanks to Charles for suggesting the aethra crab!\n\nAethra crabs look like little rocks, although some people (who must be REALLY hungry) think they look like potato chips:\n\n \n\nA hermit crab using a light bulb bottom as an inadequate shell:\n\n\n\nThe tiniest hermit crab:\n\n\n\nGimme shell pls:\n\n\n\nTHE BIGGEST HERMIT CRAB, the coconut crab. It really is this big:\n\n\n\nShow transcript:\n\nWelcome to Strange Animals Podcast. I\u2019m your host, Kate Shaw.\n\nWe have a bunch of crustaceans this week! I\u2019m sorry I\u2019ve taken so long to get to Charles\u2019s suggestion of aethra crabs, so we\u2019ll start with those.\n\nThere are four species of aethra crabs alive today, and they live in warm, shallow coastal waters. They like areas with lots of rocks on the sea floor, because the crabs look like small flattened rocks. They can tuck their legs under their carapace so that they don\u2019t show at all, and often algae and other marine animals like barnacles will attach to the carapace, increasing the crab\u2019s resemblance to a little rock. What eats rocks? Nothing eats rocks! So the aethra crab is safe as long as it stays put with its legs hidden. It lives throughout much of the world\u2019s tropical oceans, especially around islands and reefs in South Asia, but also around Australia, Mexico, and Hawaii.\n\nWe don\u2019t know a whole lot about aethra crabs, not even how many species there really are. There are probably undiscovered species that no one has studied yet, but we do know they used to be even more widespread than they are today. Twelve million years ago, for instance, a species of aethra crab lived in what is now Ukraine, with fossil remains only described in 2018.\n\nMost aethra crabs only grow a few inches across, or maybe 6 cm, but the walking rock crab of Mexico can grow to 6.3 inches across, or 16 cm across. It\u2019s light brown with lighter and darker speckles that give it a mottled appearance like a small rock.\n\nBecause they\u2019re so flattened with rounded edges, and because some species are pale in color, aethra crabs are sometimes called potato chip crabs. I don\u2019t like that name because it makes them sound tasty and not like little rocks. I think we have established that they really look like little rocks.\n\nThat\u2019s just about all I can find out about the aethra crab, so if you\u2019re thinking of going into biology and aren\u2019t sure what subject to study, may I suggest you focus your attention on the aethra crab and bring knowledge about them to the world.\n\nSo let\u2019s move on to a different type of crab, the hermit crab. A big part of being a crab is evolving ways to not be eaten. I mean, that\u2019s what every animal wants but crabs have some novel ways of accomplishing it. Some crabs look like tiny rocks, some crabs hide in shells discarded by other animals.\n\nThere are hundreds of hermit crab species, which are generally grouped as marine hermit crabs and land hermit crabs. There\u2019s also a single freshwater hermit crab that lives on a single island, Espiritu Santo, in the south Pacific, and in fact only in a single pool on that island. It was only described in 1990 and is small, less than an inch long, or about two and a half cm. It uses the discarded shells of a snail that also lives in its pool.\n\nThat\u2019s the big thing about a hermit crab: it uses the shells of other animals as a temporary home. Like all crabs, the hermit crab is an invertebrate with an exoskeleton. But unlike most crabs, its abdomen isn\u2019t armored. Instead it\u2019s soft and vulnerable, but that\u2019s okay because most of the time it\u2019s protected by a shell that the crab wears. In most species the abdomen is actually curved in a spiral shape to better fit into most shells.\n\nWhen a hermit crab finds an empty shell, it may quickly slip out of its current shell and into the new shell to see if it\u2019s a good fit. Ideally the shell is big enough for the crab to hide in completely, but not so big that it\u2019s awkward for the crab to carry around.