Antiviral activity (99.5% inhibition) against the Autographa californica polyhedrosis nuclear virus AcNPV+GFP was shown by a polypeptide of approximately 10 kDa, isolated from the exoskeleton of Pleuroncodes planipes, the pelagic red crab. This thermo-stable polypeptide retained its anti-viral properties after being exposed to 76 °C for 30 min and showed no apparent cytotoxic effect. Its anti-viral activity was observed when incubated with the virus, previous to the inoculation of cells. Using Tandem Mass Spectrometry (LC/ESI-MS/MS), this polypeptide showed sequence identity to a fragment of a myohemeritrin-like metalloprotein found in the Scoloplos armiger sea worm (VFYANLDEEHK). Copyright © 2011 Elsevier Ltd. All rights reserved.