Integrated Ocean Drilling Program Expedition 320/321 at Site U1338 (equatorial Pacific Ocean) recovered lower–middle Miocene (17–13.5 Myr) sediments containing unusually well-preserved and diverse planktonic foraminifera. Previous taxonomic study of planktonic foraminifera from this interval in the eastern Pacific Ocean has been hindered by the absence of biogenic carbonate. Here we present a taxonomic analysis of these foraminifera, including wall textures and species variability, supported by scanning electron micrographs. Specimens exhibit open pore spaces, little evidence of calcitic overgrowth on the wall surface, and in many cases spines. Fifty-five species are recorded, including Dentoglobigerina juxtabinaiensis n. sp. Dominant genera include Paragloborotalia and Globigerinoides with common Dentoglobigerina.

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