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Linked specimens: London, UK; NHM (PM PF 45683)
Current identification/main database link: Globorotalia plesiotumida Banner & Blow 1965
The test consists of three whorls of chambers; the successive whorl heights are in the approximate ratios l : 4 : 8. The test is completely evolute dorsally and the dorsal walls of all the chambers are translucent and uniformly perforate; the dorsal surface of the early whorls is clearly thickened by secondary laminae, but the surface is smooth, not pustulate, and the perforation distribution and density is not appreciably affected, nor is the chamber arrangement obscured. The dorsal surface is smoothly convex, but the dorsal chamber walls are uninflated. The dorsal intercameral sutures are very weakly depressed between the last two or three chambers only; the sutures between the earlier chambers are flush with the surface of the test (because of the lamina! thickening) but are marked by continuously developed, flush or very slightly raised, sutural limbations of imperforate, clear shell material. The globular proloculus (c. 0·010 mm diameter) is surrounded by a whorl of five reniform chambers, with smoothly curved intercameral sutures. The succeeding whorl, of six chambers, possesses straighter intercameral sutures, which are oblique to the very weakly lobulate spiral suture at angles of about 45°. The proximal ends of the later sutures become increasingly re-curved, so that in the last whorl (of 6 + chambers) the inner ends of the intercameral sutures are approximately sub-radial, only their distal parts being curved to meet the periphery obliquely. The axial periphery is acute and is furnished, throughout ontogeny, with an imperforate carina which is continuous with the dorsal sutural limbations. In axial profile, the last-formed chamber is slightly concave immediately ventrally to the carina. The ventral surface of the test is slightly more strongly convex than the dorsal surface, the ratio of ventral to dorsal convexity being about 3 : 2. The ventral side is completely involute, only the six and one-half chambers which comprise the last whorl being visible. The ventral intercameral sutures are narrowly and shallowly depressed, are nearly straight or very slightly curved or sinuous, and are radially arranged, meeting the weakly lobulate periphery and the narrow, almost completely closed tunbilicus approximately at right angles. The ventral chamber walls are finely and uniformly perforate, the pores, being spaced at distances no greater than 0·01 mm, being approximately equal in size and density of distribution to those of the dorsal surface. Most of the ventral surface is smooth, but granules are developed in the immediate vicinity of the umbilicus on the four earlier chambers of the last whorl as well as on areas of the walls of the first two chambers which immediately face the aperture. The last-formed chamber possesses a low, rounded umbilical shoulder; this shoulder is visible, to a decreasing extent, on the two preceding chambers, but it is concealed on earlier chambers of the last whorl by intorcameral embrace and overlap. The apertural face is flattened and broad; it is broadest near the axial periphery, where it is slightly concave and is delimited by the carina, and narrowest near the umbilicus; at its mid-point, the breadth of the apertural face is approximately equal to one-half its total length. The apertural face is separated from the ventral face of the last chamber by a change in slope; the area of the change is rounded (not sharply angular), and the texture and structure of the apertural face and the ventral wall are very similar. The narrow, interiomarginal aperture extends from the tunbilicus almost to the ventral margin of the peripheral carina; the aperture, which is a low arch, broadest just dorsal to its mid-point, is furnished, throughout its length, with a narrow, uniformly developed lip
Size: The maximum diameter of the test is 0.52mm
Extra details from original publication
Globorotalia (G.) tumida (sensu stricto) differs from G. (G.) tumida plesiotumida in developing a much larger test at the same growth stage (as determined by the number of chambers attained), with a much more rapid increase in whorl height (successive whorl heights being in the approximate ratios 1: 4: 12). G.(G.) tumida tumida also characteristically differs from G.(G.) tumida plesiotumida in possessing a much more massive carina, thicker test walls, a greater development of coarse granules on the earlier chambers of the ventral side, a tumid test of approximately equal dorso-ventral convexity (that is, dorsal heightjventral depth being in the approximate ratio 1 : 1) and often in possessing a higher aperture, furnished with a very broad, thick lip.
Banner, F. T. & Blow, W. H. (1965c). Two new taxa of the Globorotaliinae (Globigerinacea, foraminifera) assisting determination of the late Miocene/middle Miocene boundary. Nature. 207(5004): 1351-1354. gs Banner, F. T. & Blow, W. H. (1967). The origin, evolution and taxonomy of the foraminiferal genus Pulleniatina Cushman, 1927. Micropaleontology. 13(2): 133-162. gs Blow, W. H. (1969). Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In, Bronnimann, P. & Renz, H. H. (eds) Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967. E J Brill, Leiden 380-381. gs
Banner, F. T. & Blow, W. H. (1965c). Two new taxa of the Globorotaliinae (Globigerinacea, foraminifera) assisting determination of the late Miocene/middle Miocene boundary. Nature. 207(5004): 1351-1354. gs
Banner, F. T. & Blow, W. H. (1967). The origin, evolution and taxonomy of the foraminiferal genus Pulleniatina Cushman, 1927. Micropaleontology. 13(2): 133-162. gs
Blow, W. H. (1969). Late middle Eocene to Recent planktonic foraminiferal biostratigraphy. In, Bronnimann, P. & Renz, H. H. (eds) Proceedings of the First International Conference on Planktonic Microfossils, Geneva, 1967. E J Brill, Leiden 380-381. gs
Globorotalia (Globorotalia) tumida plesiotumida compiled by the pforams@mikrotax project team viewed: 20-1-2020
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