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If you look at this episode and think, "Oh, ho hum, think I'll skip this one because snore, jellyfish," you are so wrong! Jellies are fascinating, creepy, and often beautiful. Come learn all about our squishy friends in the sea! A Portuguese man o'war. Creepy as heck: A lion's mane jelly. You do not want this guy on your ship. Incidentally, a lot of the photos you find of divers with enormous lion's mane jellies are fakes that make the jellies look gigantic. The cosmic jelly, a deep-sea creature: The creepy Stygiomedusa gigantea, guardian of the underworld: A newly discovered golden jelly. Further reading: Jelly Biologist (I've been enjoying browsing this site) Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week’s episode is about jellyfish—also called jellies, which is more accurate since they’re not fish at all. Originally, I was going to focus on the Portuguese man o’war, another in the ongoing feature of “animals that scared me as a kid” and technically not even a jelly. But there’s so much to learn about jellies that we’re going to cover a whole lot more than that. Jellies are interesting animals, to say the least. Their bodies have radial symmetry, meaning they’re the same in all directions. While the body shape varies, most jellies have a bell-like shape. The bell is generally rather thin, made up of an external covering, an internal covering, and an elastic gel-like material in between. Inside, the jelly has a digestive cavity with four to eight oral arms surrounding the mouth and long tentacles hanging beneath. The jelly also has a simple nerve net that can detect light and react to other stimuli, and which takes the place of a brain. Jellies don’t have brains. They don’t have hearts, specialized sensory organs, or much of anything else. But they’ve been around for some 650 million years, possibly much longer, so clearly it all works. The jelly’s life cycle is pretty weird. Most start out as polyps that stick to rocks or shells and use their little tentacles to catch microscopic organisms. A polyp can bud, producing new polyps that are clones of the original. Eventually, a polyp will constrict its body and develop into a stack of larvae. Each larva develops into a tiny jelly, which separates from the stack and swims away. Once it’s grown, a jelly reproduces by releasing sperm, if it’s male, which the water carries to the female to fertilize her eggs. Some female jellies have brood pouches on the oral arms, some just carry the fertilized eggs inside the body while they develop. The embryos develop into swimming larvae called planula, which leave the female and attack themselves to something firm, where they transform into polyps. This seems needlessly complicated, but again, it works for the jelly. Polyps can live for years, while adult jellies, which I’m delighted to report are called medusas, usually only live a few months. The immortal jellyfish throws another step into this process. It can transform back into a polyp from any stage of its life if it needs to. As a polyp, the immortal jellyfish is tiny, only about a millimeter long. As a full-grown medusa it’s not all that much bigger, less than four millimeters in diameter. Because it can transform back into a polyp as many times as it needs to, apparently without any kind of degradation or injury, the immortal jellyfish is effectively, well, immortal. Before you get too excited, though, keep in mind that there’s not a whole lot of research into the immortal jellyfish yet. It’s not even known if they will transform back into polyps in the wild, since it’s only ever been observed in captivity. Almost all jellies have stinging cells, usually concentrated on the tentacles or oral arms, which they use to stun and kill prey. The stinging cells contain venom-filled nematocysts, which are coiled structures that uncoil and sting when touched.