“Q: woa are upside down jellyfishs actually always upside down? how do they swim?”
WELL MY FRIEND, they actually don’t! Or, not much, at least.
Some cnidarians (jellies & co) have a pretty neat adaptation in that they have an endosymbiotic relationship with zooxanthellae - a fancy way of saying that they have photosynthetic algae that live right inside of them. The algae gets protection and food in the form of waste, and the host gets delicious, delicious photosynthesized goodies.
Most true jellies do not, of course, entirely rely on photosynthesis, but Cassiopea jellies hang out in shallow water, and it works for them. They can swim, just like a normal jelly, but they usually prefer to just hang out. As a super bonus fun fact, because of this tendency to endlessly chill, they’re also a fairly common accessory for the carrier crab to cart around as protection
Photo from Tim Laman
Even though you didn’t ask and likely don’t care*, coral (the “& co” part of Cnidaria) also has a pretty integral relationship with zooxanthellae! Coral is made up of millions of polyps (think perpetual baby jellies) that secrete a calcium carbonate skeleton - a skeleton that would be entirely white without the various species of algae living within. Endosymbiosis!! So perfect!!!!!
Photo from Shutterstock
JUST KIDDING the relationship isn’t perfect, and depends on an extremely delicate balance. You’ve heard of “coral bleaching” (usually in conjunction with global warming), where wild corals are slowly losing their trademark colour - which, when you take into account where that colour is coming from, is actually much more serious than it sounds**.
The stress of a change in water temperature can actually cause cnidarians to lose their cool (pun intended) and kick out the algae as a sort of last-ditch attempt to save themselves. This would be a great strategy if the stress was, say, an infection or parasite, and not the inescapable slow burn of the entire planet.
Photo from Luiz Rocha/California Academy of Sciences
So the algae leaves, the coral starves, and millions of other organisms have to go find a new home. Except, of course, all the corals are doing it, so pretty soon there won’t be any homes to go to. Coral bleaching is no joke and I got super sidetracked from the whole point of this message but whatever
*But I care and that’s all that really matters so sit the heck down and get out your notebooks class
**This is facetious. How can you hear “bleaching” and think that doesn’t sound serious???? how do people still think this isn’t a big deal????? WHAT IS WRONG WITH YOU