<p>The Romualdo Formation of the Araripe Basin is one of the most important Cretaceous paleontological units in the world. Its deposition is directly related to the fragmentation of the Gondwana supercontinent during the Aptian–Albian, which resulted in marine ingressions into northeastern Brazil. The macroinvertebrate associations found in this formation provide important insights into the palaeoenvironmental history and palaeogeography of the Araripe Sea, which are still poorly understood. The present study reports on the most complete inventory to date of macroinvertebrates from this unit, with identification of associations that allowed to detail the marine subenviroments. The Spinicaudata association represents a transitional environment. The associations of the Brachyura and the Naticidae is typical of beach zones. The <i>Eocallista</i> sp. and Corbulid associations highlight mixohaline areas sensitive to changes in sea level. The associations of the Cassiopidae, Epitoniidae, and Bakevelliidae, represent shell beds formed in shelf under storm action with varying biotic conditions. The association of the Echinoidea represents the establishment of calm, shallow marine waters, which are only occasionally affected by storms. The <i>Brachidontes araripensis</i> association represents both a hypersaline lagoon and the colonization of a shallow sea following the action of storms. Lastly, the <i>Paleomattea deliciosa</i> association characterised by a necktonic shrimp represents the open marine shelf environment. The distribution patterns of marine taxa identified indicate the occurrence of marine ingressions into the Araripe Basin during the late Aptian–early Albian through the west, corroborating the hypothesis of a seaway in northeastern Brazil from the Parnaíba Basin.</p>