Ensis americanus (Binney) is an alien razor shell living infaunally in the southern North Sea. It is encrusted postmortem by the acorn barnacle Balanus crenatus Brugière. A remarkable shell of E. americanus was found densely infested by a single spatfall of B. crenatus on the inner and outer surfaces of both valves. The ligament was still attached and was pliant when collected, indicating that infestation was soon after death, probably only weeks or months before it was collected. The evidence of this specimen argues strongly against the common received wisdom that borings or encrustations on the inner surfaces of disarticulated fossil bivalves are an indication of a relatively long postmortem residence time on the seafloor.