Sea nettles.

We went to the Monterey Bay Aquarium yesterday but, owing to the whims of the kids we were with (our own plus some friends), I didn’t get to spend the hours I usually like to spend staring at jellies.
In fact, I was able to park myself in front of a single tank of jellies for maybe 15 minutes.
However, the tank contained sea nettles (Chrysaora fuscescens), jellies which are fairly gorgeous and hypnotic. It didn’t quite make up for the oppressively loud background music piped into too many of the exhibits, but it gave me a brief interval of awe.

Of course, the folks at the aquarium are cheating a little by putting these orange jellies in a deep blue tank. In the open waters, I don’t think it’s a sure thing that their background is a complementary color.

They are very pretty this way.

Also, looking at the sea nettles while they’re in a tank, you can appreciate the frilly swirl of mouth-arms and tentacles without having to think too hard about what it would feel like to float into them. As the name suggests, sea nettles can sting. They have stinging cells on their dangly bits that they use to paralyze their prey before using the mouth-arms to transfer the stunned sea life to their mouths.

While sea nettles aim to sting (and eat) fish larvae and little fish, their stinging cells would work perfectly well on humans, too. I’m guessing that would be a much less relaxing way to interact with them than, say, watching them drift across the tank.
There are indications that populations of coastal jellies like the sea nettles are on the rise, due at least in part to human influences on coastal environments. Since they eat zooplankton as well as larval fish, sea nettles are part of a complicated food web that might be shifting its balance. It’s hard to know at this point the extent to which climate change is connected to increased populations of jellies, but marine scientists are trying to figure it out.