Twenty-eight specimens of the introduced diplopod Anadenobolus monilicornis (Spirobolida: Rhinocricidae) were collected in Key Largo, Florida and examined for parasitic intestinal nematodes. Two rhigonematid species, Heth mauriesi Adamson, 1982 and Ruizia karukerae Hunt, 1999 were discovered at 100% prevalence. The morphology of both species was verified by light and scanning electron microscopy. These species represent the first United States records for members of the genera Heth and Ruizia. The rich rhigonematid fauna in the Caribbean region, which has been documented on islands such as Cuba, Guadeloupe, and Puerto Rico, indicates the potential for future additional introductions of rhigonematids to North America.