New internal and external structures are described from unusually well-preserved specimens of the acritarch genus HoegklintiaDorning 1981, recovered from the Lower Silurian Osgood and Estill shales of Kentucky and Estill Shale of Ohio (U.S.A.). The morphological variability of internal features ranges from irregularly dispersed organic remains and clusters of circular bodies within the vesicle, to structures congruent with the contours of the vesicle and processes. External bodies are primarily ovoid, and may have a ‘tube-like’ extension penetrating the vesicle interior. Published studies mention and/or depict Hoegklintia with dispersed internal organic matter, but the specimens illustrated here are the first to exhibit morphologically discernible contents. Evidence suggests that these various entities represent coagulated cell contents, life-cycle stages, or manifestations of parasitism/mutualism.

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