Catalog - Globigerina seminulina

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Globigerina seminulina

Citation: Globigerina seminulina Schwager 1866

Type specimens: P. 44035 - neotype designated by Banner & Blow 1960

Description of neotype: The fairly large test consists of about two whorls of rapidly enlarging, inflated chambers arranged in a low trochospire, with 4 chambers present in the last whorl. The chambers are initially obscure but probably embracing; they become increasingly well separated, slightly radially elongate and ovoid during the last whorl. The equatorial profile is sub-oval, somewhat elongate in the direction of the last chamber; the equatorial periphery is strongly lobulate. The axial profile is a compressed oval, and the dorsal surface is only very slightly convex. The axial periphery is evenly rounded, tending to become subacute over the last chamber. The dorsal sutures are initially obscure. In the last whorl, the intercameral sutures are slightly but broadly depressed on the ventral and dorsal surfaces and are much more deeply depressed over the periphery. The dorsal intercameral sutures are slightly curved to nearly radial, whilst the ventral intercameral sutures are virtually radial. The umbilicus is broad and probably very deep (infilled in the neotype) and is bordered by broad, clear, hyaline, thickened, crenulate and corrugated flanges, which are the strongly developed lips of the relict parts of the primary apertures of the chambers in the last whorl. The primary aperture is believed to be a low interiomarginal, intraumbilical arch, but it is obscured in the neotype. There are no supplementary apertures present, either dorsally or ventrally. The waH is very thick and coarsely perforate. The surface of the test is covered by a layer of clear shell material which is thickest near the umbilicus; this cortex partially or wholly covers the coarse but sparsely distributed punctations. [Banner & Blow 1960]

Maximum diameter of neotype: 0.56 mm. [Banner & Blow 1960]

FROM BANNER & BLOW 1960:

Taxonomic remarks: Schwager first described this species in 1866 using specimens obtained from the Neogene of Kar Nikobar, British India. Metatypic specimens were sent by Schwager to H. B. Brady and these are deposited in the British Museum (Natural History). As we have been informed by Prof. M. Reichel (personal letter dated 14th July, 1959) that the Schwager Collections in Munich have been lost, we have re-investigated this metatypic material (see also taxonomic remarks under Globigerina conglomerata). A slide present in the British Museum (Natural History) collections is labelled "Pliocene? Kar Nikobar, ex Dr. Schwager, Globigerina seminulina Schwager;" on the reverse of this slide a label is pasted, and this reads, "Globigerina zeminulina [sic] Schwager, Pliocaen, Kar Nicobar, KI." This latter label is probably in Schwager's handwriting. From among the specimens it contains, one metatype has been isolated and this is now registered in the British Museum (Natural History) as specimen number P. 44035. This specimen is here described, illustrated and proposed as neotype of Globigerina seminulina Schwager. [Banner & Blow 1960]

Remarks: We refer this species to the genus Sphaeroidinellopsis Banner and Blow 1959 because of its external cortex, secondarily thickened flange-like lips and the absence of supplementary apertures (see Banner and Blow, 1959). The taxonomic importance of the presence or absence of supplementary sutural apertures is confirmed by a study of this species. No comparable form is known which does possess such sutural supplementary apertures; Sphaeroidinella dehiscens, for example, is distinct both in morphology and stratigraphic range. It is therefore unlikely that the contention that supplementary apertures are merely reproductive features is tenable (compare Hofker, 1959).

No specimens which could be referred to Sphaeroidinellopsis subdehiscens (Blow) were present in Schwager's metatypic series; one specimen appeared similar to the form described as Globigerina kochi Caudri 1934, but the type of Caudri's species needs re-examination. The age given by Schwager on the slide sent to Brady is doubtful and they are, in our opinion, much more likely to have come from the Middle or Upper Miocene. However, A. G. I. P. Mineraria have illustrated specimens from the Lower Pliocene of Italy but this uppermost part of its range needs further investigation. It may be found that it does not occur above the Sarmatian; the stratigraphic evidence given by A. G. I. P. Mineraria is not documented. It has been recorded by Blow (1959, p. 198), from beds as old as the "Globigerinatella insueta/ Globigerinoides triloba"" Subzone, Tocuyo formation, which is here considered to be Middle to Upper Aquitanian.

Blow (op. cit., lac. cit.) has already discussed the evolutionary trends seen in this species and he refers to a plexus of evolving forms which may be shown by future work to be taxonomically distinguishable at subspecific level. Forms described as Sphaeroidinella disjuncta by Finlay (1940) are particularly closely related to Sphaeroidinellopsis seminulina and may prove to be fully synonymous. Other forms which have close affinity are Globigerina kochi Caudri 1934; Sphaeroidinella rutschi Cushman and Renz 1941 (holotype only) and Globigerina grimsdalei Keijzer 1945. These may, in part, prove synonymous amongst themselves but they are at least subspecifically distinct from S. seminulina (Schwager). [Banner & Blow 1960]

References:

Banner, F. T. & Blow, W. H. (1960a). Some primary types of species belonging to the superfamily Globigerinaceae. Contributions from the Cushman Foundation for Foraminiferal Research. 11: 1-41. gs O

Schwager, C. (1866). Fossile Foraminiferen von Kar Nikobar, Reise der Oesterreichischen Fregatte Novara um Erde in den Jahren 1857, 1858, 1859 unten den Befehlen des Commodore B. Von Wuellerstorf-Urbair. Geologischer Theil, Geologische Beobachtung no. 2, Palaeontologische Mittheilung. 2: 187-268. gs O

CATALOG OF ORIGINAL DESCRIPTIONS: Globigerina seminulina Schwager 1866

Globigerina seminulina

References:

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