Trichurispora wellgundis n. g., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae) is described from the adults of the water scavenger beetle Tropisternus collaris (Coleoptera: Hydrophilidae) collected from B A Steinhagen Lake in the Cherokee Unit of the Big Thicket National Preserve, Tyler County, Texas, U.S.A. Trichurispora is distinguished from known genera of Hirmocystidae by a distinct “trichurisiform” oocyst that is hesperidiform in outline, comprising a fusiform oocyst with shallowly ovoid terminal knobs or caps. Oocyst residua are present but confined to a central fusiform residuum vacuole. Adult and larval hydrophilid beetles represent distinctly different opportunities for parasite colonization and diversification. Gregarines have been reported from both adult and larval hydrophilid beetles, but no species and no genus is reported from both adult and larval hosts. In fact, gregarine taxic richness is often more disparate between adult and larval beetles of the same species than between host beetle species. This is the first report of a septate gregarine from an adult hydrophilid beetle in the Nearctic.