From one of my past posts:
There are three main types of reef aquarium “pods,” Copepods, Amphipods, and Isopods. You appear to have the last and rarest of the bunch, isopods, specifically Munnid isopods. They are harmless and, like the other “pods,” feed on detritus and algae, while also serving as live food for larger organisms. I hope this helped!
Here is a video: