hitch hicker id

Hello and thank you for all the great info I have been lurking for months. I finally pulled the trigger and got some Gulf Live Rock. It has been awesome watching things pop up the last couple days.so much life clams and starfish countless feather dusters sponges and algae. I have been searching...

Can someone help me identify what this is on the bottom of my montipora cap? It retracted when I accidentally touched it. It’s been there quite sometime. And I never thought anything about it. It has gotten twice as big. I attached three photos and a video of it moving. I can’t tell if it’s a...