Abstract
ABSTRACT Cibicidoides and Planulina are common genera of benthic foraminifera used for paleoceanographic reconstructions through the study of their stable isotopes (e.g., δ18O, δ13C) or morphological features (e.g., pore patterns). Often with an epifaunal mode of life, species of these genera are recognized as reliable indicators for assessing bottom water conditions. Hence, precision in their taxonomic identification is necessary for their effective utilization in paleoceanographic studies. To establish criteria for a consistent classification system of selected recent Cibicidoides and Planulina species, stereomicroscope and SEM imaging, manual illustration, and observations were conducted for specimens from surface sediment samples at the continental margin of Chile and Peru (12–44°S) in the Southeast Pacific, one of the most understudied regions worldwide. In the study area, Cibicidoides wuellerstorfi specimens showed morphological variation, differing mainly in the suture curvature, chamber inflation, and umbilical side convexity, with two morphotypes: C. wuellerstorfi forma convexa, and C. wuellerstorfi forma plana. Cibicidoides lobatulus showed differences in test shape, primarily attributed to chamber deformation from substrate fixation adaptation. Cibicidoides ungerianus is reported for the first time in the Southeast Pacific, characterized by a keeled, primarily biconvex test, inflated chambers, coarse pores on both sides, transparent test, and glassy sutures. While Planulina ariminensis and P. ornata may resemble C. wuellerstorfi, they can be distinguished by their evolute and nearly parallel umbilical and spiral sides, a large planispiral test for the former and raised umbilical sutures for the latter. Planulina limbata stands out from the other species described herein due to its raised sutures, involute umbilical side, and elongated, narrow chambers on the umbilical side. Therefore, species of Cibicidoides and Planulina might exhibit similarities; however, significant morphological differences take place among them. The criteria developed here will serve as essential tools for future applications in the Southeast Pacific, particularly for taxonomy-based proxy calibrations and paleoceanographic reconstructions.
Published Version
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