Catalog - Eoglobigerina eobulloides simplicissima

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Eoglobigerina eobulloides simplicissima

Citation: Eoglobigerina eobulloides simplicissima Blow 1979

Type age (chronostrat): Basal Paleocene, lowermost Danian, zone Pa (Globorotalia (Turborotalia) longiapertura partial-range zone); nine paratypes (pl. 70, figs. 5, 6, 9, 10 and pl. 73, figs. 1-3, 8, 9) from lower Danian, Zone P. I (Globorotalia (Turborotalia) pseudobulloides/ Eoglobigerina eobulloides simplicissima concurrent-range zone.

Type locality: DSDP Site 47/2, cored at a depth of 2689 meters on the Shatsky Rise, lat. 320 26.9' N. , long. 1570 42.7' E. , northwestern Pacific Ocean; holotype (pl. 55, fig. l) and two paratypes (pl. 55, figs. 2-4) from sample I l 6, 148-150 cm; three paratypes (pl. 57, figs. 3, 4; pl. 60, figs. 2, 3) from sample I l 5, 148-150 cm; four paratypes (pl. 70, figs. 5, 6, 9, 10) from sample I l 3, 0-5 cm; five paratypes (PL 73, figs. 1-3, 8, 9) from sample I l I (figs. l, 3, 8, from top of sample, and figs. 2, 9, from 148-150 cm).

The very small test is coiled in a fairly low trochospire with about 11-12 chambers comprising the spire and with four chambers present in the last convolution of the test. In dorsal aspect, the chambers are inflated, slightly appressed and embracing. The dorsal intercameral sutures are broadly depressed to slightly incised and are radially disposed. The chambers enlarge fairly slowly but regularly and evenly within the progression of the trochospire. In ventral aspect, the chambers are also inflated but are slightly appressed and embracing with distinct ventral intercameral sutures which are radially disposed. The umbilicus is open, quite sharply delimited by the inflated ventral surfaces of the last whorl of chambers and is quite deep. The aperture is a moderately highly arched opening almost confined to the limits of the umbilicus; however, the aperture is slightly asymmetrically placed with respect to the centre of the umbilicus and has a thin porticus. The equatorial profile is lobulate but oval in outline. The axial-apertural profile is smoothly rounded. The wall is perforate and the mural-pores open into small porepits without distinct inter-pore ridges.

Maximum diameter of holotype 0.152 mm as measured electronically.

The morphotypes ascribed to Eoglobigerina eobulloides simplicissima Blow, 1979, are all very small and, in many ways, homeomorph [sic] the gross morphology of the forms ascribed to Globigerina bulloides d'Orbigny. The three primary type specimens illustrated on pl. 55, figs. 1-4, were carefully chosen for morphological identity and these three specimens illustrate the typical morphology of the writer's new taxon. The specimen shown m axial-apertural view in fig. 3 is also examined at higher magnification in fig. 4 where the nature of the apertural system is examined in particular. The porticus is clearly shown as being a structure additional to the primary wall of the last chamber and not a simple direct reflexed continuation of the wall of this chamber. The size of the pore-pits is variably developed for specimens referable to the new taxon but the pore-pit pattern appears to be constantly expressed.
Eoglobigerina eobulloides simplicissima differs from E. eobulloides eobulloides (Morozova) [Globigerina (Eoglobigerina) eobulloides, 1959] in having a consistently four-chambered last whorl to their tests and in having chambers which enlarge a little more rapidly in the progression of the trochospire. Thus the diameters of eobulloides eobulloides are virtually equal and the equatorial profile nearly circular but in eobulloides simplicissima the diameter which bisects the last chamber is longer than the one at right angles to it. Thus, these diameters are distinctly unequal and the equatorial profile is oval and elongate in the direction which includes the last chamber. The aperture of simplicissima is a more widely open, laterally restricted, opening than seen in eobulloides eobulloides whilst the umbilicus is more clearly defined and deeper in the writer's new taxon as compared to the condition seen in Morozova's taxon. These features are seen particularly well in the paratype figured on pl. 57, figs. 3 and 4 and may be compared With the features of the [intermediate] specimen figured on the same plate in figs. I and 2. These latter figures refer to a morphotype referred to as E. eobulloides cf. simplicissima which links typical simplicissima to typical eobulloides sensu stricto.
The paratypic specimen illustrated on pl. 60, figs. 2 and 3, show a range of variation for the new taxon. In fig. 2, the elongate nature of the test is more pronounced than usual whilst in figure 3, the aperture is not so widely open as usual. The specimen in fig. 3 may show the beginnings of a transition towards the Subbotina triloculinoides triloculinoides (Plummer) [Globigerina triloculinoides, 1926] group and this transition is apparently continued by such forms as that specimen illustrated on pl. 70, fig. 7.

References:

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Eoglobigerina eobulloides simplicissima Blow 1979

Eoglobigerina eobulloides simplicissima

References:

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