its a featherduster.
i know the things ive described are not amphipods. but another reef said they are harmless.
ive seen some sundial snails in the tank and for the most part have taken out everyone ive come across but they could still be the problem. im going to search for spiders tonight. if it is spiders what should i do? i pretty much can not take that rock out without ripping apart the whole tank.