Catalog - Acarinina acarinata

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Acarinina acarinata

Citation: Acarinina acarinata Subbotina 1953

Type specimens: Pl. 22, figs. 4-10, X 72: 4, holotype; 5-10, "originals." In all figures, a indicates a dorsal view, b a ventral view, and c a peripheral view.

Type age (chronostrat): Holotype and four "originals" (nos. 4129-4132) from the Paleocene-lower Eocene, zone of flattened Globorotalias, Globorotalia crassata subzone, series F1. Other "originals" from the same zone, in the lower part of a series of white, slightly greenish, marls ("white series"); and found also in the undifferentiated lower Paleogene and in the Goryachy Klyuch horizon.

Type locality: Holotype and four "originals" (nos. 4129-4132) from near Nalchik, along the Kheu River, Northern Caucasus, U.S.S.R. Other "originals" from the Kyzyl-Espe well in the Akmol Range, Mangyshlak, Kazakh A.S.S.R. Found also in the lower Paleogene in the west and central parts of the Northern Caucasus; and in the Goryachy Klyuch horizon at the Kuban River, Northern Caucasus.

This species is reminiscent of Acarinina rotundimarginata Subbotina in general appearance and test dimensions, differing mainly in having longer and less broad chambers, due to which the test outline is oval. In addition, most often this species has four chambers in the final whorl, and only comparatively few forms are found with five chambers, whereas in Acarinina rotundimarginata in most cases there are five chambers in the final whorl and specimens with four chambers are considerably less common. Dorsal side less convex than the ventral, and often even slightly flattened. Ventral side strongly convex, nearly semispherical. Umbilicus small, a weakly defined depression near the ends of the umbilical chambers. Peripheral margin broadly rounded. Keel lacking. Chambers on dorsal side nearly oval; nearly triangular on the ventral side.

Early chambers in a distinctly exposed rotaloid spiral, often raised above the general surface of the test. The dimensions of the early chambers in comparison with the dimensions of the later chambers, which constitute the final whorl, are always very slight. In transverse section the early whorls constitute about one-third of the diameter of the entire test.

Later chambers situated in a Globigerina-like fashion, as in all rounded Acarininas. However, the attachment of the later chambers to one another is very tight so that the test outline is usually slightly sinuous, but not lobate, as is often observed in Globigerina-like chamber arrangements.

Chamber dimensions in the final whorl increase markedly in comparison with one another, so that each chamber is considerably larger than the preceding one. Sutures simple, depressed, slightly curved. Aperture slitlike, small, along the marginal suture between the umbilicus and the peripheral margin of the test. A small lip in the shape of a thin, very narrow, smooth border is often seen. Wall finely and densely spinose. Sutures, as is usual in most rounded Acarininas, are shorter on the dorsal side and longer on the ventral.

[Dimensions. -Diameter 0.35-0.55 mm.; thickness 0.25-0.35 mm. Oval tests are found, in outline and situation of chambers slightly resembling flattened Globorotalias, especially in those instances in which the first and third, as well as the second and fourth chambers are located opposite one another in the last whorl. However, no flattening of the peripheral margin, i. e., a transition from a keelless form to one with a keel, has ever been noted in Acarinina acarinata, as it has in Globorotalia.

References:

Olsson, R. K., Hemleben, C., Berggren, W. A. & Huber, B. T. (1999). Atlas of Paleocene Planktonic Foraminifera. Smithsonian Institution Press, Washington, DC. (85): 1-252. gs

Subbotina, N. N. (1953). Foraminiferes fossiles d'URSS Globigerinidae, Globorotaliidae, Hantkeninidae. Bureau de Recherches Geologiques et Minieres. 2239: 1-144. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Acarinina acarinata Subbotina 1953

Acarinina acarinata

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