Systematic updates of the agglutinated foraminiferal genus Colominella Popescu, 1998: insights from sectioned specimens

The occurrence of agglutinated foraminiferal specimens belonging to the genus Colominella Popescu, 1998 was documented for the first time by Mancin et al. (2012) in a lower Pliocene record of the western Mediterranean area, thereby extending the known stratigraphical and geographical distribution of the genus previously limited to the middle Miocene (Badenian) of the Paratethys. Direct comparisons with entire and sectioned topotype specimens of Colominella paalzowi (Cushman, 1936), recently sampled in the Badenian type locality of Lăpugiu de Sus (Transylvania), show that the Pliocene individuals from the western Mediterranean morphologically resemble the type species C. paalzowi but they also differ in possessing a longer biserial chamber arrangement with a higher number of internal chamber partitions, in lacking a clear early triserial stage, and in having a more complex microstructure of the agglutinated wall, with the grains selected with respect to their size, disposition with the test wall and mineralogical composition. Mancin et al. (2012) interpreted these peculiar shell features as evolutionary adaptations to perform kleptoplastidy and/or to house photosymbionts probably at shallower bathymetries in warm-water environments. The fact that the Pliocene individuals from the Mediterranean appear as more evolved with respect to the Badenian specimens from Paratethys represents an interesting evolutionary development of the genus Colominella that begs a further question: are the Pliocene Mediterranean specimens described by Mancin et al. (2012) correctly assigned to the Miocene species C. paalzowi or they do represent a new and more highly evolved species?