What is this polyp looking thing?

[GothFishKeeper]

A couple weeks ago I added a half pound piece of live rock to my nano as an island for the mushroom I’m planning on adding. Today I noticed this really small thing that looks kind of like a polyp on the rock near a hole. Any idea what it could be? There’s also a similar looking one towards the back of the rock as seen in the second picture. They both flow with the current and occasionally close up really fast as if they’re trying to catch things. The video I’m attaching is a zoomed in clip of the first one moving with the flow. Should I leave them be or are they gonna become something bad?

 

[lil sumpin]

Looks like a ball anemone

 

[exnisstech]

What is that!! A R2R guide to common new tank hitchhikers.

One of the greatest things about starting a reef tank is getting your live rock in and admiring all the diversity within it. The rock comes to life different creatures. This is a guide that I, along with a very well known critter identifier @KJ , have put together for the new reefer on what...

www.reef2reef.com