Catalog - Globorotalia (Turborotalia) acostaensis pseudopima

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Globorotalia (Turborotalia) acostaensis pseudopima

Citation: Globorotalia (Turborotalia) acostaensis pseudopima Blow 1969

Type age (chronostrat): Pliocene, zone N.21 (= Globorotalia (T.) tosaensis tenuitheca Consecutive-range zone), Sarmi Formation. Ranges from the base of Zone N.20 (Pliocene) to Recent

Type locality: Holotype (figs. I -3) and two paratypes (figs. 4, 5) from sample Ba.14 recovered from the Sarmi Formation in the Otim River section, Island of New Guinea, West Irian.

The large test consists of 10 chambers arranged in a low trochospire with 4 ½ inflated, subspherical chambers in the final whorl (only 4 chambers visible ventrally). The chambers are closely appressed; the ventral intercameral sutures are not deeply incised but are shallow. The umbilicus is small, almost closed and the ventral shoulder of the final cham ber overhangs the umbilicus. The aperture is interiomarginal, umbilical-extraumbilical and extends slightly beyond the mid-plane of the periphery and thus encroaches slightly onto the dorsal side. The aperture is a low arch and is bordered by a thickened rim-like lip which is 'tucked' under the inflated apertura] face of the final chamber. The spire is strongly depressed and does not protrude above the plane of the dorsal surfaces of the last whorl of chambers. The ventral intercameral sutures are subradial and the dorsal spiral suture is indistinct. The wall is calcareous, radial hyaline, moderately densely perforate and the pores open into comparatively small but deep pits. The early parts of the test tend to be rather rugose but the final chamber is relatively smooth without distinct hispidity.

Maximum diameter of holotype 0.56 mm.

This taxon develops from Globorotalia (T.) acostaensis acostaensis by reduction of the number of chambers in the last whorl, almost complete loss of the apertural lip and the acquisition of more inflated chambers. As in G. (T.) acostaensis humerosa there is a tendency for the aperture to approach a hastigerine condition but a truly symmetrical equatorial aperture has not been seen in G. (T) acostaensis pseudopima. G. (T.) acostaensis pseudopima greatly resembles G. (T) opima opima and virtually completely homeomorphs this form. However, G. (T.) opima opima occurs in the middle to later parts of the Oligocene whilst G. (T) acostaensis pseudopima occurs from the Pliocene to Recent. Gross morphological distinction between the two taxa is difficult to formulate in words but subtle differences of wall texture (and '?structure) are present. The evolution of pseudopima is clearly displayed in the Pliocene and, thus, the taxon is stratigraphically isolated from G. (T.) opima opima. The homeomorphy between pseudoptima and opima (s.s.) parallels the homeomorphy seen between G. (T.) centralis and G. (T) inflata (see Banner and Blow, 1967 Micropaleontology, vol. 13, no. 2, pp. 145, 146). In these cases intra-specific variation may be as great or even greater than the interspecific variation, it is this intra-specific variation which makes differential diagnosis difficult to formulate even though the two taxa concerned are most distinctive within the assemblages in which they occur.

References:

Blow, W. H. (1969). 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. 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

CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia (Turborotalia) acostaensis pseudopima Blow 1969

Globorotalia (Turborotalia) acostaensis pseudopima

References:

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