In a pen shell, that is! Museum friend and collaborator Amy Tripp from Marco Island took this great photo of a pinnotherid crab (arrow) inside a pen shell (probably a Stiff Pen Shell, Atrina rigida). Pinnotherids are tiny, soft-bodied crabs that live inside the mantle and gills of some bivalve mollusks (and the occasional large gastropod such as a true conch (family Strombidae) or abalone (Haliotis species). Pinnotherid crabs are commensals, i.e., they take advantage of their hosts' meals or leftovers for their own feeding.