Sony F-717 digital, tripod 9.7mm (Macro) at f2.04 1/30 at ISO 160

Wheeeee!

How could I pass up a scene like this?

Porcelain Crabs (either Petrolisthes armatus or Porcellana sayana) usually perch atop rocks in order to feed, giving them the best flow of water for filtering microorganisms. In a pinch, they'll use any handy surface that fits the bill, such as the shell of this large Thinstripe Hermit Crab (Clibanarius vittatus). Thinstripe hermits get fairly sizable, this one inhabiting a shell just slightly smaller than my fist. I didn't retain him very long in the tank, because there wouldn't be enough for him to eat.

Crabs often avoid direct, face-to-face contact, because crab species will indeed feed on one another, but they seem to know what's safe, too -- these two Porcelains are completely blasé about the much larger species. And you may also note that they don't seem to care how close they are to each other, either. During feeding, I've seen them wave a pincer to get another encroaching Porcelain to back off about a centimeter, but that's about it.

Hovering there in space is a snail species climbing the aquarium glass. Another species of hermit crabs often use shells this small as their own homes, so you have an indication of the size disparity between Thinstripes and others. Also visible, just under the shell opening of the Thinstripe, is a Slipper Snail, seen here, happy to ride along and snag its own food.