Crabs feel pain (Science Magazine)
"Plunge a live crab into a pot of boiling water, and it's likely to try to scramble out. Is the crab's behavior simply a reflex, or is it a sign of pain? Many scientists doubt that any invertebrate (or fish) feels pain because they lack the areas in the brain associated with human pain."
Crabs 'feel and remember pain' suggests new study (CNN)
"The study, which was carried out by Professor Bob Elwood and Mirjam Appel from the School of Biological Sciences at Queen's University, Belfast, looked at the reactions of hermit crabs to small electric shocks. It was published in the journal Animal Behaviour."