Forty-four specimens of the millipede Narceus gordanus Chamberlin, 1943 (Spirobolida: Spirobolidae) were collected from Alachua, Citrus, Hernando, and Marion counties in peninsular Florida. Morphometric data were recorded for each. Nematodes were dissected from the intestine of each individual and sorted into morphotaxa. Heth pivari n. sp. (Oxyuridomorpha: Ransomnematoidea: Hethidae) was found in 33 (75%) of dissected N. gordanus and examined with brightfield, differential interference contrast, phase contrast and scanning electron microscopies. LSU rDNA sequences of representative males and females of H. pivari n. sp. were analyzed and compared to sequences of nematodes in the infraorder Rhigonematomorpha. Heth mauriesi, an introduced species, also was sequenced. Females of H. pivari n. sp. differ from those of other Heth spp. in having smooth, button-like somatic and cervical papillae and shallow, shield-like cervical collars. Males have slit-like or narrowed, rather than circular, stomal openings. Heth pivari n. sp. is the first species of this genus found in an indigenous millipede north of Mexico. Keys based on female cervical ornamentation are provided to differentiate the 52 known Heth spp.
Keywords: Nematoda, 28S rDNA, biogeography, commensalism, Diplopoda, Heth mauriesi, key, molecular analysis, taxonomy.