Maranhites isaacsonii sp. nov. was recovered from an outcrop sample of the Upper Devonian Cabanillas Group, Oxapampa Province, Peru. This acritarch displays the discrete equatorial thickenings that characterize the genus, but differs from all described species by having a lobate vesicle margin with processes or process groups. The processes taper distally and terminate in capitate, rounded, or clavate tips. The palynomorph assemblage is dominated by marine elements, including acritarchs, prasinophytes, scolecodonts, and chitinozoans. The occurrence of Retispora lepidophyta indicates a Late Famennian–Early Tournaisian (Fa2c-Tn1a) age for the sample yielding Maranhites isaacsonii sp. nov. Palynomorphs exhibit a thermal alteration index equivalent to gas-window maturation.