Catalog - Globigerina nepenthes delicatula

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Globigerina nepenthes delicatula

Citation: Globigerina nepenthes subsp. delicatula Bronnimann & Resig 1971

Type locality: South West Pacific, Eauripik Ridge, Micronesia-New Guinea: DSDP Leg 7, Hole 62.1,

Type repository: Washington; USNM

The relatively large-sized in its early portion, bluntly-rounded, high trochospire consists of more than 12 chambers with 5 chambers in the last whorl. The early chambers of the trochospire are masked by secondary shell substance. The chambers are sub-globular on the spiral side and elongate-pointed toward the umbilicus, as seen in lateral and umbilical view. The final chamber is peripherally broadly rounded and rests across the umbilicus on the antepenultimate and penultimate chambers. This somewhat obliquely off-set and towering position on the final chamber is typical of the forms of the nepenthes group. The umbilicus is open and exposes the aperture of the penultimate chamber. The cameral sutures of the final whorl are well-defined on umbilical and spiral sides and fairly deep between the last chambers of the trochospire, creating for this portion of the test a slightly lobate outline.

The aperture, about 175 microns wide and 70 microns high, is a large broad arch crossing from ante-penultimate to penultimate chambers. It is bordered by an upturned imperforate smooth-walled to minutely pustulate, narrow rim of about 10 microns thickness.Very minute pustules occur laterally on the inside of the rim. This rim does not fuse with the apertural wall,which is thin, perforate, and in its lower portion covered with only poorly developed, bluntly rounded, individual pustules. The other portions of the surface of the ultimate chamber are stronger pustulate. The pustules start to coalesce laterally, developing an initial polygonal meshwork. The outer wall formations of the earlier chambers of the final whorl are by contrast very strong. The pustules in the spaces between the wall pores, of about 5 to 10 microns in diameter, fuse basally and laterally forming the funnel-shaped polygonal compartments, each surrounding a deeply set pore. The pustules in the polygonal corners are pointed and higher than the sharp-edged interconnecting walls. The polygonal surface pattern on the spiral side of the early chambers is masked by secondary shell substance. The pustules and the polygonal walls show on the scanning micrograph of the holotype, Plate 1, Figure 7,a smooth surface and nothing can be said about their ultrastructure. The holotype coils to the left.

The maximum diameter of the holotype is about 375 microns; its axial height-without the ultimate chamber—is about 250 microns. The ultimate chamber is about 100 microns high and 175 microns wide. The specimen is from Hole 62.1, Core 13, Section 2, 36-38 centimeters, Zone N. 18. It is illustrated on Plate 1,Figure 7.

Globigerina nepenthes delicatula Brönnimann and Resig, n. subsp., is distinguished from Globigerina nepenthes nepenthes Todd, 1957, by the relatively large, thin-walled, almost transparent, broadly rounded final chamber, the large aperture, and by the upturned smooth-walled, unfused with the apertural wall, rimlike lip. We have examined the holotype of Globigerina nepenthes nepenthes in the collections of the U. S.National Museum and have found that the ultimate chamber is much smaller than the preceding ones, that it lies tightly over the umbilicus, and that the aperture is a very low, elongate arch provided with a strongly pustulate, rounded border which is not upturned.

The features of the specimens illustrated on Plate 1, Figures 4 and 6, and by Blow (1969, pi 14, fig. 5) correspond closely with those of the holotype. The specimen illustrated by Plate 1, Figure 9, under the name of Globigerina nepenthes picassiana Perconig,1968, is interpreted as a subspecies of Globigerina nepenthes nepenthes. According to Perconig (1968), Globigerina nepenthes picassiana has the same stratigraphic range as Globigerina nepenthes nepenthes, which in this author's stratigraphy extends from the Tortonian to the lower Pliocene. The scanning micro-graphs of paratypes, Plate 1, Figures 1, 2 and 10,exhibit a minute granulation on the surface of the final chamber and on the upturned apertural border. The large pustules and the interconnecting walls of the polygonal meshwork of the preceding chambers are made up of small pustules or "crystallites"". As Globigerina nepenthes nepenthes and Globigerina nepenthes delicatula coexist in the same samples, we do not think that these subspecies are environmental variants, but rather that the phenotypic differences are genotypically controlled. The maximum diameter of paratypes of Globigerina nepenthes delicatula range from about 150 to 475 microns. They coil both to the left and to the right."

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 nepenthes subsp. delicatula Bronnimann & Resig 1971

Globigerina nepenthes delicatula

References:

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