The test wall of ?Nubeculina Cushman 1924 (Miliolida): updates on its agglutinated-porcelaneous wall structure from entire and sectioned specimens

Abstract

There is a growing number of new foraminifera with agglutinated wall types held together by secreted crystallites of high-magnesium calcite that do not fit within the traditional definition of the Miliolida. In this study, we analyzed entire and sectioned foraminiferal specimens frommodern marine sediments collected off the Croatian coast (Adriatic Sea) using an Environmental Scanning Electron Microscope (ESEM) equipped with Energy-Dispersive x-ray-Spectroscopy (EDS). The investigated specimens resemble the miliolid genera Nubeculina Cushman 1924 and Falsonubeculina Amao and Kaminski 2019, but display characteristics of testmorphology and an agglutinated-porcelaneous wall structure that have not been previously observed in similar miliolids. Their wall structure is more like that observed in primitive agglutinated foraminifera such as Lagenammina rather than in true miliolids. New taxonomical inferences regarding the nubeculinid group of genera are discussed.