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Species Globigerina borealis Brady 1881


Discussion / Comments:
Iaccarino (1985):
The species is better known as Globigerina pachyderma. Banner & Blow (1960) proposed the adoption of G. borealis instead of G. pachyderma (Ehrenberg), which has to he regarded as a 'nomen dubium' (Blow, 1969). In fact the taxon given by Brady (1878, pl. 21, fig. 10) as Globigerina bulloides arctic variety, corresponds well to G. pachyderma, while the figure given by Ehrenberg as Aristerospira pachyderma is not clearly recognizable. Brady (1878) regarded G. borealis as 'a thick walled, cold water variety of Globigerina bulloides' and in 1881 named it 'borealis' but did not figure it. Subsequently, in 1884, he illustrated it (pl. 114, figs. 19-20) and considered it as a synonym of G. pachyderma. From Ehrenberg's original illustration (1873, pl. 1, fig. 4) it may be seen that Aristerospira pachyderma is a thick walled form but not so clearly representative of the species as the specimens of Brady. In my opinion the type figures given by Brady both in 1881 and in 1884 correspond well to the species concept while the lectotype, illustrated by Banner & Blow (1960, pl. 3, figs. 4a-c) does not fully reflect Brady's illustrations. G. borealis shows great variability both in shape and in the calcification of the test. In particular, the last chamber is often variable in size and sometimes appears to be no more than a broad flap covering the aperture of the penultimate chamber. In other specimens it is abortive and may resemble a bulla. The aperture in such specimens may be umbilical extraumbilical in position, giving a Globorotalia like appearance to the test. Bandy & Theyer (1971) observed that there is a relationship between growth, development of the abortive last chamber and calcification. Normal development of the last chamber and thin wall are typical for the upper water column specimens. From bottom sediments come specimens with moderate calcification with an abortive last chamber becoming dominant. The advanced stage of calcification gives rise to specimens with a thickened wall, very restricted aperture and oval to subglobose test shape. Studies of this species suggest restriction of sinistral populations to Antarctic and Arctic waters, and dextral form, to warmer areas (Bandy, 1960, 1968). Bandy ( 1960, 1968) emphasized the stratigraphic significance of the coiling ratios in G. borealis; sinistral forms, limited to cold waters, can be used to separate Pleistocene from Pliocene sediments.
Synonym list:
Iaccarino (1985):
1878 Globigerina bulloides d'Orbigny. - Brady : p.435 pl. 21, figs. 10a-c arctic variety
1881 Globigerina bulloides borealis Brady. - Brady : p.412
1985 Globigerina borealis Brady. - Iaccarino : p.301 figs. 5.6a-c; 4
Was used in synonym list of:
Globigerina pachyderma Ehrenberg 1861
References:

Brady,H.B. (1878):
On the reticularian and radiolarian Rhizopoda (Foraminifera and Polycystina) of the North Polar Expedition of 1875-1876 . Ann. Mag. Nat. Hist. London Vol. 5(1) p. 425-40

Brady,H.B. (1881):
On some Arctic Foraminifera from soundings obtained on the Austro Hungarian North Polar Expedition of 1872-1874 . Ann. Mag. Nat. Hist. London Vol. 5(8) p. 393-418

Iaccarino,S. (1985):
Mediterranean Miocene and Pliocene planktic foraminifera.
In: Plankton stratigraphy Eds: Bolli, H.M.Saunders, J.B.Perch-Nielsen, K. p. 283-314
Anonymous: Unedited TaxonConcept data
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