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Subspecies Globigerinoides trilobus fistulosus Schubert 1910 | ||||||
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| Discussion / Comments: | ||||||
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Bolli & Saunders (1985): The reason why the long ranging and stratigraphically insignificant G. trilobus subspecies are included here is because they are often dominant in tropical/subtropical assemblages and because they form the stock from which some shorter ranging index forms have branched off, such as the G. bisphaericus Praeorbulina Orbulina lineage and, in the Pliocene, G. trilobus fistulosus. Banner & Blow (1960) designated a typical Globigerinoides specimen, which in the literature would be regarded as G. trilobus, as a lectotype for the apparently lost holotype of Globigerina quadrilobata d'Orbigny, 1846 (Fig. 20.18).According to d'Orbigny's original description and figures his taxon possessed no secondary aperture. For direct comparison we reproduce here the original illustrations (Fig. 20.18) and those of the lectotype (Fig. 20.17) at approximately the same magnification. The lectotype was selected by Banner & Blow from a heterogeneous topotypic collection deposited in Paris. Subsequently some authors followed Banner& Blow's new concept of G. quadrilobata. Bandy (1964) in discussing and illustrating this case concluded that the lectotype designated by Banner & Blow for G. quadrilobata is invalid in that it represents not only a different species but also a different genus compared with the original type figure. We agree with Bandy and consequently place Banner & Blow's lectotype of G. quadrilobata (Fig. 20.17) in synonymy with Globigerinoides trilobus immaturus (Fig. 20.14). Bolli (1957) distinguished the subspecies trilobus from the subspecies immaturus by the possession of a final chamber larger than all earlier chambers combined A comparison of Reuss' holotype figures of triloba and LeRoy's immaturus (Figs. 20.15 and 20.14) makes evident that, though in the holotype figures of immaturus the final chamber is slightly smaller in relation to the early test compared with trilobus, the difference is minimal. Blow's lectotype for quadrilobatus (Fig. 20.17) with its much larger sized early stage compared with the last chamber, reflects a typical immaturus subspecies in the sense of Bolli (1957). Forms with an ultimate elongate sack like chamber are placed in G. trilobus sacculifer. In the Pliocene and Pleistocene there evolve from G. trilobus sacculifer some bizarre forms where the final one to three chambers form at their peripheral ends fistule like extensions, varying in shape, number and length. Such forms are generally placed in G. trilobus fistulosus (synonym: G. quadrilobatus hystricosus Belford, 1962). On closer examination the following three types can be distinguished, two of which are of stratigraphic significance: (1) G. trilobus fistulosus s.s. (Figs. 22.5 11): fistules distinct, finger like, with rounded ends, one to several in last chamber, often present in penultimate, less frequently in earlier chambers. Chambers which possess more than two to three fistules, are usually distinctly flattened and of a cockscomb shape. Where several fistules occur they usually are in line along the periphery of chambers, like fingers on a hand. Figs. 22.5 11 illustrate some of the considerable variability of the taxon as regards number of fistules and shape of chambers. Range: within Globorotalia margaritae evoluta Zone to top of Globigerinoides trilobus fistulosus Subzone. (2) Globigerinoides trilobus cf. fistulosus (Fig. 22.4): Fistullose extensions generally confined to the last chamber, but much less extended and not as finger like as in G. trilobus fistulosus Observed range: Globorotalia margaritae margaritae Zone to Holocene. (3) Globigerinoides trilobus 'A' (Figs. 22.1 3): Final 1 3 chambers strongly elongated, somewhat irregular in shape, fistuIes of varying length and diameter, often with a pointed end, not arranged in line, may branch off from chamber at different points and angles. Individual fistules may also branch. Such forms have been observed in the Caribbean restricted to the Late Pleistocene to ?Holocene. |
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| Synonym list: | ||||||
| Bolli & Saunders (1985): 1910 Globigerina fistulosa Schubert. - Schubert : p.323 text-fig.2, figs. 13a-c no holotype designated
1985 Globigerinoides trilobus fistulosus Schubert. - Bolli & Saunders : p.197 figs. 22.5-11; 7,10,11
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| References: | ||||||
Schubert,R.J. (1910): Bolli,H.M. and Saunders,J.B. (1985): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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