My grandparents have a beach house on the Cape, on the bay side. When the tide is low you can walk out for over a mile, and in the tidal flats are little tiny hermit crabs (http://pics.livejournal.com/bleemoo/pic/0000t7h5/) that are small enough that they are physically unable to break human skin, so you can just pick them up and let them crawl on your hand.

For the first 10 years of my life or so I thought that was the only kind of hermit crab, and I got very confused whenever anyone talked about getting pinched by a hermit crab.