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Translation from the Russian. - Test small. round in plan view. with a high. slightly twisted spire consisting of three whorls: there are 3-4 small, slightly convex chambers in the initial whorls. in the last whorl 4 to 6. On the dorsal side the chambers are usually alate, barely convex, with flat, translucent, often limbate sutures: on the ventral, conically vaulted, side the chambers are triangular, making an angle with the outer margin of about 45°: the surface of the chambers is slightly convex, umbilical ends usually closely touching: intercameral sutures fine, radial, slightly depressed. Outer margin bluntly acute, less commonly sharp, no keel, Surface covered wth fine spinules.
Size: holotype diameter 0.28 mm height 0.21 mm
Extra details from original publication
Variation. - The basic defining character of this species is its weakly developed spire, with each whorl projecting a little above the next one. Among the many specimens the overwhelming majority have this characteristic. but in some forms only the last half-whorl is slightly uncoiled. and the initial whorls are nearly coplanar. A distinctive, but nonetheless variable, feature is the vaulted nature of the conicospiral ventral side of the test, which is, however, not observed in all specimens owing to flattening of the chambers, the tightly apprcssed umbilical ends of the chambers sometimes open and form a small umbilicus.
Features that vary broadly are: chamber shape on the dorsal side (from flat, alate to slightly convex. rounded-rectangular), number of chambers in the last whorl (usually 5, but often deviating from this number- 4-6), the outer margin (usually bluntly acute, nearly rounded. but sometimes sharp and slightly lobate), size of the last chamber (in 4-chambered forms making up almost half the whole test. in forms with 5 or 6 chambers sometimes much smaller than the preceding one).
Comparative remarks. - Despite the wide variability noted this subspecies has completely diagnostic features and is easily distinguished from Acarinina angulata (White) [Globigerina angulata, 1928], to which group it belongs, by the high and Iittle twisted spire. From A. tadjikistanaensis (Bykova) [Globorotalia tadjikistanaensis, 1953] the many specimens collected from the Crimea and Northern Caucasus differ in having fewer chambers (4-6. usually 5, not 6-8), and a more rounded outer margin. Considering that the principal features - the slightly twisted spire and the vaulting of the spiroconvex chambers on the ventral side - are common to the Central Asian species. While the main differences are the number of chambers and the shape of the outer margin, it would evidently be more accurate to consider these specimens as a subspecies of A. tadjikistanaensis (Bykova), which has a different aureole of distribution. Further study, and also a comparison of originals (up to now not carried out) will allow us to determine its systematic position more precisely.
Holotype (fig. 7a-c) from Tarkhankut reference borehole, Crimea: other figured specimen (fig. 6a-c) from along the Bodrak River. Bakhchisaray area, southwestern Crimea: and also found in dark grey calcareous clays of the lower part of the Upper Paleocene in the Dzhanay reference borehole. northwestern Caspian Basin: all in the southern USSR. Single specimens at the first locality, in massive quantities at the other two.
djanaensis was included by Davidzon (1976) in the list of species included in Igorina, when he described the genus.
Davidzon, R. M. (1976). Novyy paleogenovyy rod planktonnykh foraminifer. [A new Paleogene genus of planktonic foraminifera.]. Trudy Vsesoyuznogo Nauchno-issledovatel’skogo Geologorazvedochnogo Neftyanogo Instituta (VNIGNI), Tadzhikskoe Otdelenie,. 183: 197-199. gs Shutskaya, E. K. (1960). Foraminifera from the Upper Paleocene of southwestern Crimea.
Davidzon, R. M. (1976). Novyy paleogenovyy rod planktonnykh foraminifer. [A new Paleogene genus of planktonic foraminifera.]. Trudy Vsesoyuznogo Nauchno-issledovatel’skogo Geologorazvedochnogo Neftyanogo Instituta (VNIGNI), Tadzhikskoe Otdelenie,. 183: 197-199. gs
Shutskaya, E. K. (1960).
Foraminifera from the Upper Paleocene of southwestern Crimea.
Acarinina tadjikistanensis djanaensis compiled by the pforams@mikrotax project team viewed: 18-2-2020
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