Help IDing new friends or foes

[vfitz2523]

I have a 20gal tank, with 3 small lps frags, 2 clowns, fire goby, blood shrimp, and 6 snails. Recently had a friend watch my tank for a week while out of town, needless to say some over feeding and an aggressive water change and I've lost the shrimp and one of my larger snails. When I went to remove the snail today I noticed this guy using the shell as a home. Any idea what I got? Should I remove the critter or let him make a home among the rocks? I tried image searching it online but couldn't get a clear enough picture so I'm hoping the friendly people here will have a sharper eye, thanks!

 

[sixty_reefer]

It’s a amphipod good snack for the fish