Morphology of Pulleniatina (planktonic foraminifera) from optical microscopy, micro-CT, and SEM investigations

Pulleniatina is a genus of planktonic foraminifera that is widely used in biostratigraphic and palaeoceanographic studies. In our taxonomy, it comprises six morphospecies, alphabetically P. finalis, P. obliquiloculata, P. praecursor, P. praespectabilis, P. primalis, and P. spectabilis. Standard methods of taxonomic discrimination rely on descriptive characteristics of the adult test, such as the shape of the chambers, the shape and position of the primary aperture, the number of chambers per whorl, the height of the spire, the degree of involution, and the irregularity of coiling (“streptospirality”). Here, we illustrate representative specimens of each morphospecies and the likely ancestor, Neogloboquadrina acostaensis, from International Ocean Discovery Program (IODP) Site U1488 (Eauripik Rise, western equatorial Pacific Ocean) using light microscopy and X-ray microcomputed tomography (micro-CT). For each specimen, we provide multifocus light microscope images in three standard orientations, a set of up to 2000 X-radiographs, and a rendered three-dimensional (3D) model that can be viewed externally, internally, and in any cross-section using widely available freeware. We also include labelled images distinguishing each successive chamber and quantify the chamber volumes, the rate of size increase, the aspect ratios, and the angles at which they are added. A second set of specimens was crushed and imaged using scanning electron microscopy (SEM) to further study the internal morphology and wall texture. We use these observations to document the comparative ontogeny and test structure of the six Pulleniatina morphospecies in the context of an evolutionary model involving two diverging species lineages.