New insight into the systematics and evolution of the foraminifera

Abstract

A new suprageneric classification of the Foraminifera is here presented based on fundamentally new concepts of their evolution and classification. The predominant significance is given to the shell morphology as the most conservative feature, while the wall composition and shell wall ultrastructure are considered as having important but nevertheless subordinate meaning. Foraminifera are regarded as a phylum that includes five classes: Astrorhizata Saidova 1981, Spirillinata Mikhalevich 1992, Miliolata Saidova 1981, Nodosariata Mikhalevich 1992 and Rotaliata Mikhalevich 1980. Each of the five classes unite forms that can be characterized by a complex of common features of their shell morphology reflecting the building plan of the organism (number of chambers, their form, the predominant mode of coiling, position and character of the aperture and its inner structures, the presence or absence of additional apertures, the presence or absence of integrative systems and their peculiarities, and some other features – all of them having evolutionary significance). Each of these classes represents independent and well-outlined phyletic lines. Some characters of the cell structure and nuclear apparatus are also used as taxonomic features of some higher-ranking taxa where the accumulated data permit. Isomorphic agglutinated forms differing from their calacareous analogues in their shell wall composition are separated as subclasses within the appropriate classes: the subclasses Ammodiscana Mikhalevich 1980, Miliamminana Mikhalevich 1980, Hormosinana Mikhalevich 1992, Textulariana Mikhalevich 1980 within the Spirillinata, Miliolata, Nodosariata and Rotaliata correspondingly (the latter also includes two calcareous subclasses – the Rotaliana Mikhalevich 1980 and Globigerinana Mikhalevich 1980).Within the class Astrorhizata, subclasses with organic (Lagynana Mikhalevich 1980) and agglutinated (Astrorhizana Saidova 1981) shell walls are included. In total, the phylum Foraminifera embraces 73 orders, 27 suborders, 98 superfamilies, 499 families and 368 subfamilies among which 2 orders (Cymbaloporida, Cassigerinellida), one suborder Duostominina, two families (Cymbaloporettidae, Haynesinidae), and two subfamilies (Cushmanellinae and Tristixinae) are described as new. The composition of the classes and subclasses is also partially revised. The largest changes were made within the classes Spirillinata, Miliolata and Nodosariata: thus the Fusulinids were included into the Miliolata, the Chapmaninids - into the Spirillinata, the Stilostomellids, Pleurostomellids and Paleozoic Nodosariids – into the Nodosariata. The former suborder Textulariina (= Textulariacea Ehrenberg 1838 sensu lata Loeblich and Tappan 1987) was shown to be heterogenous and its representatives are split out into several subclasses of the different classes according to their shell morphology. The composition of the subclasses is here given up to the family level; most of the subclasses need further revision at the family and generic level. Under the new approach the morphologically similar agglutinated and calcareous shells within each class could be regarded as closely related rather than convergent forms. The rise and development of the classes took place independently and in parallel in each of the phylogenetic lines examined.