Description of a new species of Maritrema (Digenea:Microphallidae) from Mar Chiquita coastal lagoon (Buenos Aires, Argentina) with notes on its life cycle.

Adults of Maritrema bonaerensis n. sp. (Digenea:Microphallidae) were collected from the intestine of the gulls Larus maculipennis and Larus atlanticus from Mar Chiquita coastal lagoon, Buenos Aires province, Argentina. The new species differs from M. pulcherrima Travassos, 1928 in having smaller sucker ratio, longer intestinal ceca, ovary not lobed, and larger eggs, and from Maritrema prosthometra Deblock and Heard, 1969 it differs in having larger suckers, smaller vitelline follicles, and in the absence of pars prostatica. It differs from Maritrema acadiae (Swales, 1933) in having larger body and pharynx and longer cirrus. It differs from Maritrema paracadiae Ching, 1974 in the larger pharynx, longer cirrus, and in the absence of prominent prostatic cells. From Maritrema majestova Ke, 1976, it differs in having a larger body, smaller eggs, and a long and protusible cirrus. Finally, M. bonaerensis differs from Maritrema chiricae Deblock, 1975 in the larger body, longer cirrus, and in the morphology of the seminal vesicle. Sporocysts and metacercarial stages isolated from the snail Heleobia australis australis and from the crabs Cyrtograpsus angulatus and Chasmagnatus granulata, respectively, suggest that those invertebrates could act as intermediate host in the life cycle of the new species in the lagoon. This assumption is supported by evidence derived from natural and experimental infections, from studies on biology of the actual and presumed hosts, as well as from previous reports on life cycles of species of Maritrema with similar transmission patterns.