Maritrema heardi is a parasitic fluke that infects the marsh rice rat (Oryzomys palustris) in a salt marsh at Cedar Key, Florida.

[2] Its intermediate host is the fiddler crab Uca pugilator[4] and it lives in the intestine of the marsh rice rat, its definitive host.

[1] Together with two other species of Maritrema, it is very common in affected marsh rice rats;[4] it infects 19% of studied rats at Cedar Key.

[3] According to Tkach and colleagues, M. heardi is probably primarily a parasite of birds that has secondarily infected the marsh rice rat.

[5] Floridatrema was distinguished from Maritrema on the basis of its possession of loops of the uterus that extend forward to the place where the intestine is forked or even to the pharynx.