Parvatrema affinis [Jameson et Nicoll, 1913] James, 1964 in the Baltic clam Macoma balthica [Mollusca: Bivalvia] in the Gulf of Gdańsk

Background. Macoma balthica is the major zoobenthic species in the Gulf of Gdańsk. Material. Two (4.2%) of the 48 M. balthica specimens collected in 2002 from the depth of 40 m were found to harbour metacercariae−containing sporocysts of Parvatrema affinis (Jameson et Nicoll, 1913) James, 1964. Results. The paper reports morphoanatomical dimensions of 30 sporocysts and metacercariae. Due to the common occurrence of the intermediate (Macoma balthica) and definitive (anseriform and charadriiform birds) hosts of P. affinis in the Gulf of Gdańsk, the trematodes are regarded as a constant component of the local biocoenose.