Coral ID - is this some kind of sun coral?

[mc-nuggs]

I found these growing on a live rock I bought from Florida. The tentacles seem to fully extend at night; they are slightly retracted during the day. Very long tentacles, like a torch coral, but translucent and speckled. They are very fast feeders, like anemone-fast. They appear to be branching, but the branching is so short, it is basically encrusting.

Been wondering what these might be for the past year or so. Any speculation welcome.

 

[ReefStable]

Those look like Aiptasia to me. They're a pest anemone that spread quickly and sting everything they touch.

Here are some tips for getting rid of them before they spread.
https://reefstable.com/solutions/pests/aiptasia

 

[F i s h y]

These are called hidden cup corals.

Hidden Cup Coral – Phyllangia americana – Tampa Bay Saltwater

 

[ReefStable]

These are called hidden cup corals.

Hidden Cup Coral – Phyllangia americana – Tampa Bay Saltwater

You may be right. I've never seen that before.

Honestly though, my general rule is if I didn't put it there, I don't trust it...

 

[mc-nuggs]

Thanks guys! These are definitely hidden cup corals