Strange growth on LR
I'm new to the aquarium hobby and recently bought some live rock for my tank. The tank is only about a week old now and I noticed there has been some rapid growth of some type of hitchhiker on my live rock but I haven't been able to figure out what it is.
It started off as a white/transparent spot on the rock but it's grown to look like some sort of slug with long antennae/tentacles. One has a purplish tint to it.
I know it's not some sort of worm or snail as it hasn't moved an inch in over a week, or when I poke it lol. I'm very curious as to what it might be, and a bit concerned as multiple have started showing up around the tank.
Any thoughts as to what it might be?