A newly discovered trematode parasite infecting the bay scallop, Argopecten irradians

Abstract

A novel parasite infecting the gill tissue of bay scallops (Argopecten irradians) was first observed in North Carolina in 2012 and has also been found infecting bay scallop populations along the Gulf Coast of Florida. Because the parasite infects a host of great fisheries interest and is extremely conspicuous to the naked eye, and yet was not observed before 2012, it is likely an introduced species. Preliminary morphological analyses indicate that this parasite is a trematode in the superfamily Hemiuroidea and that it uses the bay scallop as a first intermediate host. All other hosts are currently unknown. Phylogenetic analyses show that this novel parasite belongs to family Didymozoidae and forms a strongly supported clade with a recently described trematode from Australia, Saccularina magnacetabula. Histological analysis indicates that Saccularina sp. sporocysts inhabit and greatly expand the afferent vessels of the host's gills. Prevalence monitoring of Saccularina sp. in caged and wild bay scallop populations in North Carolina shows a strong pattern of seasonality that is consistent across sites, but no latitudinal gradient was found, suggesting that prevalence is likely driven by final host distribution in time and space. This research provides important baseline information on the basic biology of Saccularina sp. and impacts on its economically important host, the bay scallop.