Those look just like the ones I have had for years. They were reproducing in my tank like rabbits. I lost count of how many I gave away. I am now down to a manageable amount of them. It has been a while since they have spawned. They all work their way to the top of coral or live rock and extend their bodies upward on the tips of their tentacles. It looks like war of the worlds. They then turned my tank into what looked like 2% milk. There were way too many in my tank at the time which is why is was so dense and hard to see in there for about 20 minutes or so.