452 MICROFOSSILS/Foraminifera Figure Fossil foraminifera, showing diversity of form of the chambered test (or shell) Left to right, they comprise the genera Ammotium, Bolivina, Planulina, Cyclammina, and Pseudorotalia, respectively The first and fourth are agglutinating foraminifera, making their test from mineral grains ‘glued’ together with an organic cement The other three are calcareous, secreted by the foraminifer itself Magnifications between Â25 and Â150 retained and the foraminiferal wall structure and composition is used at the highest taxonomic level, the eight main systematic groupings within the Foraminifera may be defined at the rank of a subclass However, in view of the elevation of the Foraminifera to the status of a phylum, the rank of these groups will probably change in the near future Pending a decision on their rank by the IWGFS, the main wall-structure groups are treated here as informal categories The main groups are the allogromiids, agglutinates, fusulinids, miliolids, silicoloculinids, robertinids, and other minor perforate aragonitic groups, the spirillinids which display a unique crystal stucture, and the perforate calcitic groups consisting of rotaliids, buliminids, and globigerinids (Figure 1) This subdivision, based on wall structure, is not strictly a phylogenetic scheme, and even separates some groups based on habitat (i.e., planktonic and benthic groups) in spite of their identical wall structure Alongside the work of Loeblich and Tappan, a conceptually different version of the higher systematics of the foraminifera (‘the Russian school’) was pioneered by Fursenko and Rauser-Chernousova, and developed in detail by Mikhalevich and others According to these authors, the starting point for the systematic hierarchy is the overall test morphology rather than wall structure The general ‘bauplan’ of the foraminiferal test is regarded to be associated with the function and habitat of the whole organism The mode of coiling and apertural characteristics of the test are considered to be the most conservative feature of the test, and the overall test shape is given priority in those cases where the test composition and/or microstructure has undergone modification within evolutionary lineages Therefore, the composition and ultrastructure of the foraminiferal wall has subordinate significance compared with test morphology Mikhalevich uses the following criteria to define the main foraminiferal classes: the number of chambers, the chamber shape, pathways of chamber formation resulting in the nature of chamber conjunction, the shape of the test and the predominant mode of coiling, the shape and position of the main aperture, the development of any inner apertural structures, the development of integrative apertural systems, the presence or absence of additional apertures, the presence of additional skeletal plates, and 10 the presence or absence of canal systems According to the Mikhalevich classification, the foraminifera are composed of a fewer number of larger groups of equal rank, and consist of the classes Astrorhizata, Spirillinata, Miliolata, Nodosariata, and Rotaliata (the latter also includes the planktonic Globigerinana as a subclass) The more advanced multichambered classes have both secreted calcareous and agglutinated subclasses (Figures and 3) In each case, the agglutinated subclass (or in the case of the Astrorhizata, the organic-walled Lagynana) is regarded to be the ancestral group Within each subclass, there are numerous examples of strikingly isomorphic pairs of Class Spirillinata Subclass Ammodiscana: Ammovertellina, Ammovertella, Ammodiscus, Turritelella, Repmanina, Arenotur rispirillina, 7a,b Tetrataxis Subclass Spirillinana: Miliospirella, Glomodiscus, Archediscus dubitabilis, A karreri, Cylindrotrocholina, Howchinia, Lasio trochus, Babelispirrillina, Coronipora, 10 Trocholina, 11 Spirillina, 12 Spirotrocholina (a,b views of the test, c view of the canal in axial section), 13 Annulopatellina, 14 Paleopatellina Class Miliolata Subclass Miliamminana: Recurvoides, 2a,b Charentia, Lituola, Alzonella, Dentostomina, Sigmoilopsis, Ammomassilina, Reticulinella Subclass Miliolana: Squamulina, Cornuspira, Cornuspiroides, Gheorgianina, Discospirina, Cornuloculina, Spirophtalmidium, Fisherinella, Zoella, 10 Spirolina, 11a,b Danubiella, 12 Quinqueloculina, 13 Neoalveolina, 14a,b Dendritina, 15 Laevipeneroplis, 16 Parasorites Class Nodosariata Subclass Hormosinana: Saccammina, Hormosinella, 3a,b,c Nodosinum, Adelungia, Pseudopalmula, Nouria, Agardhella, Flabellammina, Triplasia, 10a,b Ammomarginulina Subclass Nodosariana: Lagena, Parafissurina, Syzrania, 4,5 Grigelis, Nodosaria, Multiseptida, 8a,b Lingulina (a microspheric, b megalospheric forms), Marginulina, 10a,b Tristix, 11 Kyphopixa, 12 Dyofrondicularia, 13 Flabellina, 14 Polymorphina, 15 Laryngosigma, 16 Lenticulina, 17 Planularia, 18 Hemicristellaria, 19 Saracenaria Class Rotaliata (the third subclass, Globigerinana, is not shown) Subclass Textulariana: Haplophragmoides, Minouxia, 3a,b Gaudryina, Pseudobolivina, 5a,b Clavulina, 6a,b Asterotrochammina, Tiphotrocha Subclass Rotaliana: Bermudezinella, Elphidium, Brizalina, Bolivinellina, Euuvigerina, Sporobulimina, 7a,b Reussella, Pseudobuliminella, 9a,b Discorbis, 10 Neoconorbina, 11 Rotalia (detail of canal system), 12a,b Ammonia, 13 Baculogypsinoides (horizontal section of megalospheric individual showing canals), 14 Eulinderina