The commensal relationship between the marine bivalve A. islandica and the nemertean M. grossa along the Atlantic coast of North America is reported. It was previously documented in European specimens. A single M. grossa was living in a small ocean quahog dredged from offshore New Jersey [USA]. The nemertean also occurred in the venerid clam, Pitar morrhuana, from the same locality with a frequency of 28%. Examination of specimens of A. islandica for M. grossa with negative results suggests this occurrence is atypical.