Catalog - Globigerina nepenthoides

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Globigerina nepenthoides

Citation: Globigerina nepenthoides Brönnimann & Resig 1971

Type age (chronostrat): Lower Miocene

Type locality: South West Pacific, Ontong Java Plateau/Soloman Rise New Guinea: DSDP Leg 7, Hole 64.1

Type repository: Washington; USNM

The small-sized test consists of about 10 to 15 chambers arranged in a moderately high but, in its initial portion, not pointed trochospire with 4 chambers in the final whorl. The peripherally broadly rounded ultimate chamber is radially and tangentially equidimensional, about 110 microns, and is placed nepenthes-like with somewhat extended and flattened ventral face across the umbilicus. The subglobular chambers increase rapidly in size except for those of the final whorl which are separated by well-incised, intercameral sutures producing slightly lobate outlines as seen in spiral and side views. The wall is calcareous, perforate, and its surface distinctly pustulate with short blunt composite pustules. The bases of the pustules are fused and surround the deeply set small rounded pores by polygonal compartments. The poly-
gonal walls are broad, rounded and minutely pustulate.

The aperture is an elongate arch, relatively low in comparison with its length and going across three chambers. It is about 100 microns long and about 20 microns high. The thin-walled slightly upturned apertural face forms a distinct, thick, irregularly finely to coarsely pustulate border. The scanning micrograph of the apertural side of the holotype, Plate 7, Figure 6, exhibits wall pores down to the apertural border.
The holotype coils to the right.

The maximum diameter of the holotype is about 255 microns, its maxi- mum axial height, without the ultimate chamber,about 150 microns. The holotype is illustrated on Plate 7, Figure 6. It is from Hole 64.1, Core 2, Section 6, 15-17 centimeters, Zone N. 7/N. 8.

Globigerina nepenthoides is homeomorphic in the above described morphologic features with Globigerina nepenthes nepenthes Todd and, in particular, Globigerina nepenthes delicatula Brönnimann and Resig,n.subsp.

In the final whorl, however, Globigerina nepenthoides is less tightly coiled and therefore more lobate than most of the individuals of the stratigraphically younger Globigerina nepenthes group, whose sub-species normally show slightly lobate to non-lobate, ovoid outlines. Reference is here made to the illustrations of Globigerina nepenthes nepenthes by Blow (1969, pi. 14, fig. 5) and in the present paper, Plate 1,
Figures 4 and 6, and of Globigerina nepenthes delicatula, Plate 1, Figures 1, 2, 3, 7, and 10. One specimen of this subspecies, Plate 1, Figure 10, shows a more lobate outline than normally seen. Although in large adults of Globigerina nepenthoides the up-turned apertural rim may be quite thick and strongly pustulate, the lip of Globigerina nepenthes nepenthes is comparatively much more strongly structured by perpendicular incisions and has a single row of regularly arranged pustules, which may fuse in its distal portion with the chamber wall as shown by the side view of Globigerina nepenthes nepenthes, Plate 1, Figure 4.
The ultimate chamber and the lip of Globigerina nepenthes delicatula, on the other hand, are thinner-walled than that of nepenthes nepenthes and approaches in this characteristic those of Globigerina nepenthoides. Typical Globigerina nepenthes delicatula have very thin upturned lips, normally almost smooth to minutely pustulate, occasionally showing a slight structuring by vertical lines. Globigerina nepenthoides differs from Globigerina falconensis Blow, with which it is associated from Zone N. 13 to the uppermost part of Zone N. 6, by its high trochospire, the nepenthes-like somewhat oblique position of the ultimate chamber, the elongate low-arched aperture, and by the upturned apertural border. Further, its wall seems to be generally thinner than that of Globigerina falconensis. The surface structures of Globigerina falconensis and and of Globigerina nepenthoides are very similar. Both species have perforate calcareous walls, and the
rounded deeply set pores are also found in Globigerina falconensis to be surrounded by bluntly pointed basally fused pustules. The relatively regularly structured lip of Globigerina falconensis is closer to that of Globigerina nepenthes nepenthes than to that of Globigerina nepenthoides. Reference is made to the illustrations of typical Globigerina falconensis, Plate 3,Figures 1, 2, and 4, and to the metatype of Globigerina falconensis figured by Blow (1969, pi. 16, fig. 1),which is not particularly well-preserved but shows the strongly structured thick wall quite well. Globigerina nilotica Viotti and Mansour, 1969, is probably indentical with Globigerina falconensis, at least in part. The illustration of this species (Viotti and Mansour, 1969, p. 447, pl. 6) shows in fact a mixture of rather different apertural morphologies. However, the individuals figured on Plate 6, Figures 1, 2, 3 and 4 could be assigned to the Globigerina falconenis group of
forms. The maximum diameters of paratypes of Globigerina nepenthoides range from 150 to 225 microns.
The scanning micrographs of paratypes Plate 7, Figures 4, 5, 7, and 9, show strongly pustulate tests. The ultimate chamber of the specimen, Plate 7,Figures 4 and 5, from Hole 64.1, Zone N. 7/N. 8, has a minutely granular texture. The polygonal meshwork is not yet developed but accumulation of small pustules or "crystallites"" indicates the position of the future large pustules of the polygonal corners. The wall pores occur on the ultimate chamber down to the apertural border. In places, the wall pores are defined by whitish thin annuli which seem to rise slightly above the surface of the wall."

References:

Brönnimann, P. & Resig, J. (1971). A Neogene globigerinacean biochronologic time-scale of the southwestern Pacific. Initial Reports of the Deep Sea Drilling Project. 7(2): 1235-1469. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina nepenthoides Brönnimann & Resig 1971

Globigerina nepenthoides

References:

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