The Guayaguayare Formation, an Upper Cretaceous (Maastrichtian) deep-water unit in southern Trinidad, contains a diverse assemblage of agglutinated foraminifera. This study presents a systematic investigation of these assemblages based on subsurface well material, providing taxonomic descriptions and evaluating their paleoecological significance. A total of 61 species belonging to 33 genera were identified, dominated by tubular and elongate forms such as Nothia excelsa, ammodiscids including Ammodiscus cretaceus and Ammodiscus peruvianus, rzehakinids such as Rzehakina epigona, and textulariids including Dorothia and Remesella. The assemblage composition corresponds to a mixture of slope marl and flysch-type faunas, indicating deposition in a deep-marine environment near or below the lysocline. Variations in morphogroup composition reflect changes in benthic conditions, including shifts in sedimentation regime, organic matter supply, and bottom-water oxygenation. The dominance of cosmopolitan taxa further supports the interpretation of broadly similar ecological conditions across deep-marine settings during the Late Cretaceous. These results provide new taxonomic data and contribute to a better understanding of deep-water agglutinated foraminiferal assemblages and their paleoecological significance in the Guayaguayare Formation.