The Samsung dishwasher has an upper rack with a rotating sprayer that was thoroughly clogged with debris from its damaged screen filter:
The whole assembly is readily available, although it seems any discrete part of the dishwasher costs about fifty bucks and this one wasn’t exactly broken.
It comes apart by rotating the lock ring (the one with right-angle ears sticking out on either side) 1/8 turn in the other direction from whichever way you think it should rotate. Hold the spray bar, shove the ears, and the spray arm will drop off:
The inside of the spray bar shows the locking details:
Now, here’s the tricky part.
The small ring under the locking ring, the one with two square nubbins pointing downward, snaps onto the pipe carrying the water. There’s a shallow notch around the pipe, the inside of the ring has a shallow lip, and the ring holds the whole affair onto the pipe.
Contrary to what I thought, the two nubbins do not latch onto anything. Apparently, they hold the ring in the proper position relative to the arm’s interior and that’s it.
The only way to reassemble the arm is to snap the small ring into place, with the lock ring above it, then install the arm and turn the lock ring 1/8 turn the other way. You (well, I) cannot snap the assembled arm into place, because the nubbins don’t provide enough oomph to seat the small ring on the pipe.
Unless I write that down, I will never remember it …
Protip: Needle nose tweezers are invaluable for picking crud out of the nozzles. Iterate on picking and flushing with water until nothing more comes out, then expect to repeat the process several times as more crud emerges from the depths of the plumbing.
Although it is apparently possible to disassemble the spray arm by unlatching all the snaps along the edge, I’d reserve that for a moment when lives depended on unclogging the nozzles.
The Smell of Molten Projects in the Morning 
The bottom-of-the-line dishwasher that Came With the House(tm) was a GE that skipped such frivolous luxuries as a filter. Eventually the bottom (I don’t recall an upper spray arm, though I’ve tried hard to forget that so-called appliance.) spray arm got clogged with crud, and I had the delightful experience of kneeling in front of the washer with filament tweezers to get the crud out. Removing either the door or the spray arm was beyond casual surgery…
The only good thing was that the crud was solid, but malleable. I was able to tease out the blockages so we could resume use. It was a day of great rejoicing when the replacement was installed. We could also do things without being drowned out by the sound of the old dishwasher. Cleaning a filter is so much better than spray arms.