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Linked specimens: London, UK; NHM (PM P 45684) London, UK; NHM (PM PF 45684)
Current identification/main database link: Globorotalia merotumida Blow & Banner, in Banner & Blow 1965
The test consists of three whorls of regularly enlarging chambers, six in each whorl; successive whorl heights are in the approximate ratios I : 2 : 5. The test is completely evolute dorsally, and the dorsal walls of all the chambers are thin, translucent and finely perforate; there is no conspicuous deposit of thick, secondary laminae to obscure the early whorls. The dorsal surface is slightly convex, but the dorsal chamber walls are but little, if at all, inflated; the dorsal sutures are very weakly depressed, but they are marked by continuously developed, slightly raised sutural limbations of clear, imperforate shell material. The spiral suture is lobulate. The globular proloculus (c. 0·015 mm diameter) is surrounded by a whorl of reniform chambers with smoothly curved intercameral sutures; in succeeding whorls, the intercameral sutures become straighter and are, in their mid-parts, oblique to the weakly lobulate spiral suture at angles of about 45°; however, the proximal ends of the later intercameral sutures may be sharply re-curved, meeting the spiral suture virtually at right angles. The axial periphery is acute and is furnished, throughout ontogeny, with an imperforate carina, which is continuous with the dorsal sutural thickenings. In axial profile, the chambers are slightly concave immediately dorsally and ventrally to the carina. The ventral surface of the test is much more strongly convex than the dorsal surface, the ratio of ventral to dorsal convexity being about 2 : I. The ventral side is completely involute, only six chambers being visible. The ventral intercameral sutures are narrowly and shallowly depressed and, throughout most of their length, are nearly straight (or only very slightly curved) and radially arranged, meeting the weakly lobulate periphery and the narrow, closed umbilicus at right angles. The ventral chamber walls are very finely perforate; the pores, being spaced at distances no greater than 0·005 mm, are approximately equal in size and density of distribution to those on the dorsal surface. Most of the ventral surface is smooth, but granules are developed in the immediate vicinity of the umbilicus on the earlier chambers and on the area of the wall of the first two chambers which immediately faces the aperture. The last-formed chamber possesses a very low, rounded umbilical shoulder; the umbilical shoulders of the earlier chambers are concealed by embracing overlap of the succeeding chambers. The apcrtural face is flattened and broad; it is broadest near the axial periphery, where it is delimited by the carina, and narrowest near the umbilicus; at its mid-point, the breadth of the apertural face is approximately equal to two-thirds of its total length. The apJrtural face is separated from the ventral face of the last chamber by an abrupt change in slope, but the area of the change in slope 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 umbilicus to the ventral margin of the peripheral carina, and it is of approximately uniform breadth throughout. The aperture is furnished, through its length, by a thick, narrow lip, which is most strongly developed towards the umbilicus.
Size: The maximum diameter of the test is 0·38 mm.
Extra details from original publication
Comparative diagnosis of species : Globorotalia (G.) merotumida typically differs from G.(G.) tumida plesiotumida in possessing (1) a test which is smaller in size at the same growth stage as measured by the numbers of chambers present, (2) a slower increase in whorl height as seen dorsally, (3) more uniformly enlarging chambers, (4) more consistently oblique dorsal intercameral sutures, (5) a thinner and more finely perforate test wall, (6) a thinner carina, (7) a relatively greater ventral convexity, and (8) a relatively broader apertural face.
G.(G.) merotumida differs from G. ( Turborotalia) lenguaensis Bolli in possessing (1) a clearly developed imperforate peripheral carina, (2) a test which has about 25 per cent greater diameter at the same growth stage, as measured by the number of chambers present, (3) a more rapidly increasing whorl height, and (4) less strongly curved dorsal intercameral sutures.
G.(G.) merotumida has a much more convex and tumid test than any sub-species of G.(G.) cultrata (s.l.) (d'Orbigny). G.(G.) ungulata Bermudez, although possessing a dorso-ventral convexity comparable with that of G.(G.) merotumida, has a much weaker carina, circumferentially longer chambers in dorsal aspect, a shorter aperture, and a much more rapid increase in whorl height.
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) merotumida compiled by the pforams@mikrotax project team viewed: 3-7-2020
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