I was watching these Chrysaora pacifica (Japanese sea nettle) strobilae pulse along in their little lab bowl, when all of a sudden one of the jelly babies popped off and swam away! These young jellies (termed ephyra) are connected to one another with the remnants of muscle fibers from the parent polyp, which run through the mouth of one ephyra, and into the bell top of the next [1]. As they pulse these connections grow weaker and eventually break.
Work Cited
[1] The morphogenesis of ephyra in Coronatae (Cnidaria, Scyphozoa)
http://link.springer.com/article/10.1007%2Fs00227-007-0719-8?LI=true
The Helm Lab Blog 
Are these your polyps? You’ve got two of the color morphs, there are several, would be interesting to know if they represent sexual dimorphism???
I was wondering about that Wyatt! Do they retain the color difference as they grow? Or should I separate them now?
Energetic little things aren’t they!
Does that mean the oral arms of one are actually holding the next jelly in place, or is there something additional there like a channel into the bell of the next? And either way it reminds me of a stack of adult Pelagia in the sea…
Yes, I think that’s what’s going on. There are small sinuous fibers of old polyp muscle running through the mouth and connecting one ephyra to the next. As they pulse these fibers grow weaker and eventually detach.