I am assuming you are refering to the annelid(segmented) worm on the left. It looks like one of the bristleworms, there are about a thousand sp. IDed. They are generaly a good thing as long as they dont get out of control, or are the Fireworm spp. that are know coral crunchers, tho I doubt it. THe spooky looking thing on the right is a little
hermit crab 
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