Evidence is accumulating for a memory-like phenomenon in the immune defence of invertebrates. Down syndrome cell adhesion molecule (Dscam) has been proposed as a key candidate for a somatically diversified receptor system in the crustaceans and insects (Pancrustacea) that could enable challenge-specific protection. However, what is the evidence for an involvement of Dscam in pancrustacean immune memory, and in particular specificity? Here we review the current state of the art, and discuss hypotheses of how Dscam could be involved in immunity. We conclude that while there is increasing evidence for the involvement of Dscam in pancrustacean immunity, crucial experiments to address whether it plays a role in specificity upon secondary encounter with a pathogen still remain to be done.