Catalog - Globanomalina laccadivensis

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Globanomalina laccadivensis

Citation: Globanomalina laccadivensis Fleisher 1974

Type repository: Washington; USNM

The minute strongly compressed test contains at leat 14 chambers arranged in a very low trochospire, with 5½ to 6½ chambers in the final whorl. The test wall is penetrated by numerous irregularly distributed pored which are not clearly visibly under the binocular microscope. In axial view, the test is distinctly rounded but slightly convex, and the early chambers are obscured by wall thickening. The dorsal sutures are curved and very slightly depressed, and the closely appressed chambers can be distinguished only with difficulty. The peripheral margin is rounded and consists os a broad imperforate band, which is particularly developed in the early chambers of the final worl. No raised keel is present. The final chamber projects above the remainder of the last whorl as seen in lateral view. The ventral sutures are straight and slightly depressed, and the chambersare more distinct and wedge-shaped in ventral than in dorsal view. The umbilicus is small and shallow and may be present only as a slight depression in smaller forms. The aperture is a low umbilical to extraumbilical arch, bordered by a faint rim, at the base of the poorly defined apertural face.

The species is named for the Laccadive Island group, which is located near Site 219.

Remarks: The relationships of G. laccadivensis with most other known species are not presently understood. It appears, however, to have evolved from G. pseudoscitula by the loss of the distinct, raised keel, rounding of the periphery, and increase in the number, size, and density of the pores. The author's concept of G. laccadivensis includes forms with a poorly developed but distinct keel and an acute periphery on the final chamber (Plate 5, Figure 11), although it may prove desirable to refer these to G.pseudoscitula. Typical forms, however, were observed at the base of the stratigraphic range recorded here for this taxon.

G. laccadivensis is quite similar to Turborotalita primitiva Brönnimann and Resig, differing primarily in having a greater number of pores, a less pustulose chamber wall, a less embracing final chamber, and more chambers per whorl. The morphology of the latter species, however, is closer to Globanomalina laccadivensis than to Turborotalita spp., and it probably should be referred to Globanomalina. There seem to be no known intermediate species throughout the stratigraphic interval separating the range of these forms, but the very small test size suggests that they may have been overlooked.

Stratigraphic Range: Middle P.14 to middle P.17 (late Middle to Late Eocene).

Problematica - Resembles an igorinid but occurs stratigraphically above the last occurrence of Igorina; we have not found this taxon in our researches; needs further study. [Huber et al. 2006, p. 507]

References:

Fleisher, R. L. (1974a). Cenozoic planktonic foraminifera and biostratigraphy, Arabian Sea, Deep Sea Drilling Project, Leg 23A. Initial Reports of the Deep Sea Drilling Project. 23: 1001-1072. gs O

Huber, B. T., Olsson, R. K. & Pearson, P. N. (2006). Taxonomy, biostratigraphy, and phylogeny of Eocene microperforate planktonic foraminifera (Jenkinsina, Cassigerinelloita, Chiloguembelina, Streptochilus, Zeauvigerina, Tenuitella, and Cassigerinella) and Problematica (Dipsidripella). In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 16): 461-508. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globanomalina laccadivensis Fleisher 1974

Globanomalina laccadivensis

References:

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