Catalog - Globorotalia (Turborotalia) incisa

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Globorotalia (Turborotalia) incisa

Citation: Globorotalia (Turborotalia) incisa Brönnimann & Resig 1971

Type locality: S W Pacific, Eauripik Ridge, Hole 62.1, Core 8, Sec.3, 15-17cm, Zone N.20

Type repository: Washington; USNM

The medium-sized test is a low, tightly coiled trochospire of about 12 chambers which increase rapidly in size and change in the course of growth from a tangentially to a radially elongate, or at least equi-dimensional, subglobular shape. The early chambers form a slightly elevated but not pointed trochospire.
There are four chambers in the final whorl. The spiral and cameral sutures of the final whorl are strongly incised, but narrow, cutting each chamber clearly from its neighboring chambers. Hence the outline of the test,as seen in spiral view, is only slightly lobate almost to nonlobate. At the intersections of cameral and spiral dorsal sutures, there occur rather deep but narrow depressions but no supplementary sutural apertures.
The cameral sutures are radial on both the umbilical and the spiral side. The radial intercameral suture between ultimate and penultimate chambers is virtually a continuation of the spiral suture separating the final chamber from the preceding coil. This characteristic is nearly the same for the intercameral sutures between penultimate and antepenultimate and between ante-penultimate and ante-antepenultimate chambers, which is probably the reason, together with the deep incision of the suture, why the chambers of the final whorl break off so easily. In lateral view, the chambers are peripherally broadly rounded and at least the ultimate and penultimate ones somewhat compressed in axial directions. In umbilical view the chambers are pointed toward the deep and small umbilicus, of about 15 microns diameter, which is large enough to expose a portion of the aperture of the penultimate chamber.
The final aperture is a low umbilical-extraumbilical arch, about 10 to 20 microns high, with a distinct but narrow and thick-walled rim-like border which, as shown on the scanning micrographs, Plate 46, Figures 1 and 8, is pustulate. The wall is calcareous, of heavy appearance, perforate, and its surface is densely pustulate. The umbilical pustules on the early chambers are heavier than those on the later ones, and pointed to bluntly rounded. The pustules which coalesce into funnel-like compartments around the deeply set pores, seem to be composed of smaller units as described for Globorotalia (T.) planispira Brönnimann and Resig,n.sp., and Globorotalia (T.) pseudopumilio Brönnimann and Resig, n. sp.

The maximum diameter of the holotype is 275 microns; its axial height is 175 microns. The specimen is illustrated on Plate 46,Figure 1. It is from Hole 62.1, Core 8, Section 3, 15-17 centimeters, Zone N. 20 (including N. 19).

The number of chambers in the final whorl varies from 3.5 to 5 in paratypes of Globorotalia (T.) incisa n. sp.
The small individuals with 3.5 to 4 chambers in the final whorl are tightly coiled, those with five chambers show a tendency to coil less tightly. The final chamber(s) in large forms break(s) off easily along the deeply incised cameral and spiral sutures. The pustulate surface and the general morphology place Globorotalia (T.) incisa, in the vicinity of Globorotalia (Turborotalia) obesa Bolli, 1957, illustrated by scanning micrographs, Plate 50, Figures 7 and 8, from which it differs by the tight coiling of the trochospire, the deeply incised cut-like sutures, the less obese shape of the final chambers, and the different surface structure. Also, the aperture of Globorotalia (T.) obesa is considerably larger than that of Globorotalia (TJ incisa.

Globorotalia (T.) incisa seems to be related to Globorotalia (Turborotalia) pseudopachyderma Cita, Premoli-Silva and Rossi, 1965, which shows throughout a tightly coiled test with 4 chambers in the final whorl.
It is illustrated by the scanning micrograph, Plate 45,Figure 8. The final chamber is, in contrast to that of
Globorotalia (T.) incisa, strongly oppressed and normally smaller than the penultimate chamber. The apertural features are identical in both species. Due to the more tight mode of coiling, the radial sutures of Globorotalia (T.)pseudopachyderma appear to be less deeply cut than those of Globorotalia (TJ incisa, but they are still distinct and sharply defined. On the ultimate chamber of paratypes of Globorotalia (T.)incisa, Plate 46, Figures 2, 3, 4, 5 and 6, the large pointed to bluntly pointed pustules are irregularly distributed and fairly widely spaced. In between the larger pustules occur numerous minute ones. The larger pustules are axially "canaliculate"" as can be seen on the scanning micrograph, Plate 46, Figure 4. The detail of the specimen, Plate 46, Figure 3, illustrated on Plate 46, Figure 7, suggests that the minute pustules are in fact short spines. Also the larger pustules of Globorotalia (T.) pseudopachyderma are ""canaliculate"". The outer wall formations of pachyderma and incisa are identical, suggesting the genetic relationship
of the two forms. Globorotalia (T.) pseudopachyderma and Globorotalia (T.) incisa are clearly closely allied and associated in most samples of the interval Zone N. 20 (including N. 19), to Zone N. 18, that is, in Hole 62.1 from Core 8, Section 3 to Core 13, Section 4. The maximum diameter of topotypes of Globorotalia (T.) incisa ranges from about 150 to 375 microns. The direction of coiling of paratypes is random."

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: Globorotalia (Turborotalia) incisa Brönnimann & Resig 1971

Globorotalia (Turborotalia) incisa

References:

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