These Jellies Will Turn You Upside-down!
Since I was raised in an aquarium, I’ll just get this out of the way… I don’t say jellyfish or starfish. As you may have noticed previously, science is an ever changing and growing field, and along with those changes sometimes names and descriptions change as well. So, in this and future posts, I will be referring to them as jellies and sea stars. Ok, the soapbox has been put away. I am so excited to get to talk about one of my favorite jellies of all time. These wonderful animals are just as special and unique as the constellation they are named after. Let’s drift on over and learn about the cassiopea jelly.
What is it? A cassiopea is a type of “true jelly”, meaning they have a cup shaped bell (the dome), and have two life phases, the polyp and the medusa (when you think of a jelly, that is usually this phase). Another name for these jellies are the upside-down jellies, which should tell you a little bit about them. They aren’t very large, and grow to be around 16 inches wide and 10 inches high. Their domes are a more flattened shape than most jellies, which makes it easier to rest on the sea floor. They have 8 arms smallish oral arms (the tentacle part) that look like lace when relaxed. They come in a range of beautiful colors with blue, grey, green, and brown being the most common. The colors come from an algae that lives within the arms. Researchers are not sure how long they live in the wild but in zoological settings, cassiopeas usually live up to 4 years.
Where do they live? Cassiopeas are found around the world in shallow, tropical coastal regions. They prefer sheltered areas like mangroves, lagoons, estuaries, and in some coastal lakes. Due to their superpower, cassiopea are found in shallow water, usually no deeper 3 feet or so. These jellies are social, and are often found in groups along the sea floor, this makes me say “awww” every time I see them.
What is their diet? This is the cool part… remember that algae I mentioned? They don’t eat that, but what is so nifty is they sort of farm it and I’ll go further into that in the superpower part. The algae is called zooxanthellae, and it fills most of the cassiopea’s dietary needs. The rest of its diet consists of zooplankton they catch with nematocysts (stinging cells).
What does cassiopea romance look like? Jellies have odd reproductive stuff that I am not qualified to explain the whole thing, so I’ll add a picture below… Anyway, when a girl jelly is ready she will lay eggs and males will fertilize them, and this is where they lose me. Parenting is not in their vocabulary either, seriously they are like 95% water. Really sorry that cnidarian (jellies, coral, anemones, etc.) reproduction is just too weird for me to try and explain.
Yep…. here you go. That’s easy to understand, you didn’t even need me to explain. This graphic is from Frontiers in Neuroscience
What is the cassiopea’s superpower? I will give these guys a solid 2.5 superpowers. Number one… Most creatures spend their lives looking for food, but not our cassiopea. They have given up the normal jelly life of drifting, for what I would call… passive farming. These jellies live upside down in shallow water, which allows the algae to get all the sunlight it needs and is protected from predators. In return, the algae produces food for the jelly. This partnership is called symbiosis, and is the definition of “teamwork makes the dream work”. Their second superpower is that they are the first species without a central nervous system that has been recorded sleeping. All I know is when they are asleep, they tend to pulse less and can be startled awake…that’s adorable. The half a superpower is that they are a jelly, so technically they can sting. In order to protect themselves and their algae friends, they will secrete a gooey, mucus substance that have stinging cells known as nematocytes in it. These stinging cells aren’t particularly harmful to people, but they will cause a very itchy rash.
How many are there? Well there are more than three….scientist disagree with how many species there are. According to the World Register of Marine Species there are eight species of Cassiopea, including andromeda, depressa, frondosa, maremetens, medusa, mertensi, ndrosia, and ornata. So, we will go with that for now, till they can decide on a concrete number.
Ranges of various cassiopea species. Credit:Lorenzito1
Science Time (and the crowd goes wild)!!!!
Cassiopea - Cassiopea This name comes from a queen in Greek mythology…I’ll explain later, but it makes sense to name an upside-down animal after her.
Cassiopea andromeda - Indo-Pacific region naturally, and invasive in the Mediterranean
Cassiopea depressa - Western Indian Ocean, off the coast of Africa
Cassiopea frondosa - Westrn Atlantic Ocean and Caribbean Sea
Cassiopea maremetens - Western Pacific Ocean, off the coast of Australia
Cassiopea medusa - Pacific Ocean around Indonesia and the Philippines
Cassiopea mertensi - Southern Pacific Ocean, around Micronesia
Cassiopea ndorsia - Pacific Ocean, around Australia and Fiji
Cassiopea ornata - Pacific Ocean from the Philippines to southern Japan
This is a first for me. These jellies are not listed anywhere on the IUCN Redlist or even on CITES….. so they’re good. Just making an honest life of farming in the tropics. Guess this is where I tell you the Greek queen Cassiopea and why it is a fitting name. Queen Cassiopea lived in Aethiopia (Ethiopia). She was very vain, and made the mistake of proclaiming her daughter, Andromeda, was more beautiful than the Nereids, the ocean nymph daughters of Poseidon. If you watched Clash of the Titans, that is their story. After she dies, Poseidon punishes her by putting her in the sky on her throne. This may not sound like a punishment, but for half the year she is upside-down, and has to cling to her chair…thus why the cassiopea jellies are named after her. This constellation was first listed by Ptolemy in the 2nd century, and is still one of the easiest constellations to find, with a distinctive W shape in the sky.
Queen Cassiopea upside down in the sky. You can see the W easily in the sky. Image from AstroBob
That’s it for this week….some jellies and greek mythology. Two things I geek out about way too much.
Resources:
Collins, A.G.; Morandini, A.C. (2024). World List of Scyphozoa: Cassiopea. World Register of Marine Species. https://www.marinespecies.org/aphia.php?p=taxdetails&id=135253
Pattern Media. (2010). Upside Down Jellyfish. Jellyfish Facts http://www.jellyfishfacts.net/upside-down-jellyfish.html.
Post, M. and Sacca, P. (2012). Cassiopea xamachana. Animal Diversity Web. https://animaldiversity.org/accounts/Cassiopea_xamachana/
