Definitley a mantis shrimp. Check out this site on some various trap methods.
Be careful, please. Mantis are awesome, but dangerous. They *can* cut you very badly, take a finger off, etc. No kidding. If you have some heavy duty gloves, that might help just to provide a little extra protection.
If you want to keep it, I'd go with a smaller acrylic tank, since it is stronger than glass. If not, the LFS
should buy it back or give you credit for it. They are in high demand by some of the more adventurous hobbyists. Haha.
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