Definition of "trematode"

He passed under the last of the bridges and around the bend in the river, through peaceful farmland, high fields tilted on the slopes and rich turned earth in patches of black corrugation among the greening purlieus and small cultivated orchards like scenes of plenitude from picturebooks suddenly pasted over the waste he was a familiar of, the river like a giant trematode curling down out of the city, welling heavy and septic past these fine homes on the north shore.

1979, Cormac McCarthy, Suttree, Random House, page 119