Hermit vs green star polyp question

I purchased a green star polyp over the weekend. The morning after I got it, woke up got ready for and noticed a small hermit crab laying on it, which must have been a hitchhiker that came with it, so I removed it and layed it on my sand band, well this morning same thing he was back on the gsp, willthis hurt gsp, or is it just using it for a sleeping spot?
 
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