Intraspecific variation in Polydora ciliata (Johnston) was assessed on the basis of evidence from morphological characters, which were studied by scanning electron microscopy. Differences were observed between populations of P. ciliata with respect to the setae of the fifth modified segment and in the caruncle. Two other species, namely P. ligni Webster and P. limicola (Annenkova), were also studied in order to assess interspecific variation. The two forms of P. ciliata, that is boring and non-boring, were found to be different morphologically.
