Is what I found a hermit crab?

Me and my freinds were in the ocean about waist deep, and she felt a shell with her foot, so she picked it up, and it was a mollusk or crab of some sort...We think its a hermit crab...but we thought those lived on land and couldnt be underwater that deep for too long or it may drown....but it looks like a hermit crab. it has six arms and feelers and eyes and a swirly shell. help?