Unknown organism (Update-terebellid worm?)

I'm not exactly sure what these are, but they don't look like scyphozoans. Due to the thickness of the tentacles, and also the fact that some of them retracted from time to time, my best guess is that this is some sort of hydrozoan, possibly even a hula skirt siphonophore. They weren't very big at all, not even 20 cm from bell to tentacle tips. The tentacles of one individual were actually moving, as in retracting, so it was still alive.
Anyway, these were found alongside many stranded Lion's mane jellyfish, a different sighting has been made for them.