Thanks to Murilo and an anonymous listener for their suggestions this week! Further reading: The ‘sheep’ that can photosynthesize Meet the ‘mold pigs,’ a new group of invertebrates from 30 million years ago A leaf sheep: Shaun the sheep: A mold pig: Show transcript: Welcome to Strange Animals Podcast. I’m your host, Kate Shaw. This week let’s learn about two animals that sound like you’d find them on a farm, but they’re much different than their names imply. Thanks to Murilo for suggesting the leaf sheep, which is where we’ll start. The leaf sheep isn’t a sheep or a leaf. It’s actually a type of sea slug that lives in tropical waters near Japan and throughout much of coastal south Asia. The reason it’s called a leaf sheep is because it actually looks a lot like a tiny cartoon sheep covered with green leaves instead of wool. Back in episode 215 we talked about the sea bunny, which is another type of sea slug although it’s not closely related to the leaf sheep. The leaf sheep is even smaller than the sea bunny, which can grow up to an inch long, or about 25 mm. The leaf sheep only grows about 10 mm long at most, which explains why it wasn’t discovered until 1993. No one noticed it. The leaf sheep’s face is white or pale yellow with two tiny black dots for eyes set close together, which kind of makes it look like Shaun the Sheep. It also has two black-tipped protuberances that look like ears, although they’re actually chemoreceptors called rhinophores. The rest of its body is covered with leaf-shaped spines called cerata, which are green and often tipped with pink, white, or black. This helps disguise it as a plant, but there’s another reason why it’s green. The leaf sheep eats a particular kind of algae called Avrainvillea, which looks like moss or fuzzy carpet. While algae aren’t exactly plants or animals, many do photosynthesize like plants. In other words, they transform sunlight into energy to keep them alive. In order to photosynthesize, a plant or algae uses a special pigment called chlorophyll that makes up part of a chloroplast in its cells, which happens to be green. The leaf sheep eats the algae, but it doesn’t digest the chloroplasts. Instead, it absorbs them into its own body and uses them for photosynthesis. That way it gets nutrients from eating and digesting algae and it gets extra energy from sunlight. This is a trait shared by other sea slugs in the superorder Sacoglossa. Because they need sunlight for photosynthesis, they live in shallow water, often near coral reefs. When the leaf sheep’s eggs hatch, the larvae have shells, but as they mature they shed their shells. This is a good place to talk about cyanobacteria, which was requested ages ago by an anonymous listener. Cyanobacteria mostly live in water and are also called blue-green algae, even though they’re not actually classified as algae. They’re considered bacteria, although not every scientist agrees. Some are unicellular, meaning they just consist of one cell, while others are multicellular like plants and animals, which means they have multiple cells specialized for different functions. Some other cyanobacteria group together in colonies. So basically, cyanobacteria looked at the chart of possible life forms and said, “yes, thanks, we’ll take some of everything.” That’s why it’s so hard to classify them. Cyanobacteria photosynthesize, and they’ve been doing so for far longer than plants--possibly as much as 2.7 billion years, although scientists think cyanobacteria originally evolved around 3.5 billion years ago. The earth is about 4.5 billion years old and plants didn’t evolve until about 700 million years ago. Like most plants also do, cyanobacteria produce oxygen as part of the photosynthetic process, and when they started doing so around 2.7 billion years ago, they changed the entire world. Before then, earth’s atmosphere hardly contained any oxygen. If you had a time machine and went back to more tha...