Spider Filter feeder? What is this?

[Gracekain]

I discovered this organism on the glass today. Initially, there were two present: this one and a very small specimen. However, by the time I retrieved my phone, the smaller one had disappeared. Based on my observations, it appears to possess filter-feeding tentacles. Obtaining a clear image was challenging due to the water flow; therefore, I reduced the flow, and the organism immediately detached and settled to the substrate. I was then able to remove it.

 

[Tahoe61]

Hydroid Jelly Fish. Fairly common in new set ups. They will disappear as quickly as they appeared.

 

[Gracekain]

That makes sense. I initially thought they resembled jellyfish. I am curious as to how it entered the tank. I double-dip my frags, both upon purchase and after quarantine, and I have utilized dry rock. Unless it somehow came in with the Fiji Pink Live Sand, I am at a loss.

 

[Tahoe61]

I don't think anyone has definitively figured out how Hydroids entire a dry rock system.