The presence of polydorids shell-borer and the epifaunal polychaetes on Crassostrea cf. brasiliana were studied in five estuaries in Northeastern Brazil. The prevalence of shell-boring polychaetes in oysters varied significantly, showing the dominance of Polydora websteri, with 57% of sampled oysters, and Boccardiella ligerica, with 11%, but the prevalence was significantly different among estuaries sampled. Capibaribe River showed the highest infestation, with 81% these mud-blisters, but in Massangana River had no presence of these polychaetes. The linear regression between the number of polychaetes and the size of oysters was significant, suggesting that infestation increases with age.
