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Narceus millipedes are known from two Canadian provinces (Québec and Ontario); every U.S. state east of the Mississippi River; and nine states to the west (Minnesota, Iowa, Missouri, Arkansas, Louisiana, Nebraska, Kansas, Oklahoma, and Texas). These large, cylindrical millipedes may reach four inches in length as adults and are commonly encountered in a wide range of habitats and within a broad elevational range in the eastern United States. (Shelley et al. 2006 and references therein)
The genus Narceus includes two valid species endemic to Florida (N. gordanus and N. woodruffi) as well as two of uncertain status which occur throughout the range of the genus and may be referred to as the “N. americanus/annularis complex”. According to Shelley et al. (2006), the N. americanus/annularis complex likely includes unrecognized cryptic species, particularly in the southern portion of its distribution. Narceus annularis appears to have a generally more northern distribution than N. americanus, with only the former reportedly found in Canada, New England, New York, New Jersey, Pennsylvania, Wisconsin, Iowa, Missouri, and Kansas; only the latter found in South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, Arkansas, Oklahoma, and Texas; and both species occurring in Illinois, Indiana, Ohio, West Virginia, Virginia, Kentucky, Tennessee, and North Carolina. Shelley et al. (2006) discuss the taxonomic history of this group and provide a thorough review and analysis of distribution records, but emphasize the need for a modern revision of the genus, including molecular genetic analyses.
Narceus americanus is a natural (and probably a primary) intermediate host of the acanthocephalan parasite Oligacanthorhynchus tortuosa. It appears likely that transmission directly from this intermediate millipede host to the definitive host (the only known definitive host being the Virginia Opossum, Didelphis virginiana) is the primary means of transmission for O. tortuosa. The work by Richardson (2006) documenting these host relationships provided the first elucidation of a life cycle of an Oligacanthorhynchus acanthocephalan and resulted in the first description of the cystacanth of O. tortuosa. Although it remains possible that the life cycle of O. tortuosa may also include intervening paratenic hosts in addition to the intermediate millipede host and the definitive opossum host (as Elkins and Nickol (1983) found was the case for another acanthocephalan that may infect millipedes, Macracanthorhynchus ingens), according to Richardson (2006) there is so far no evidence of any paratenic hosts for O. tortuosa (see general discussion of acanthocephalan life cycles under Acanthocephala). In addition to O. tortuosa, Macracanthorhynchus ingens, a common acanthocephalan parasite of the raccoon (Procyon lotor), has also been reported from N. americanus (in fact, this was the first report of an acanthocepalan from a millipede) (Crites, 1964), although cystacanths were not reared to adulthood to verify the identification or life cycle (Elkins and Nickol 1983).