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Subspecies Globorotalia (Turborotalia) tosaensis tosaensis Blow 1969 | ||||||
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| Discussion / Comments: | ||||||
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Blow (1969): Remarks: During the writers investigations into the morphology and taxonomy of forms occurring in the Pliocene Pleistocene it became apparent that two forms existed which differed mainly in terms of their wall structure, although differences in coiling and chamber shape and arrangement were also present. These forms were similar in gross morphology to the illustrated morphology of Globorotalia tosaensis. The writer contacted Dr. TAKAYANAGI who kindly sent details of the morphology of the holotype of tosaensis over and above the published description and especially details of the wall structure of the form. Further, TAKAYANAGI kindly sent several paratapes of G. tosaensis. These paratypes together with TAKAYANAGI's fürther information indicated that "Globorotalia tosaensis" had what appeared to be a "thickened wall". However, recent optical and electron microscope stereoscan studies indicate that this "thickened wall", characteristic of tosaensis sensu stricto, is a complex structure and not merely due to some exogenous, ecophenotypic and secondary thickening by random secretion of calcareous material upon a "thin walled" specimen resultant upon a change of habitat during ontogeny. Thus both "thick" and "thin" walled forms occur in the samples from the Sarmi formation, West Irian, in great profusion and none of these samples contain foraminiferal assemblages indicative of a depth of deposition greater than about 250 metres at the most. As discussed above for G. (T.) crassaformis ronda (P. 388) and later in the discussion for G. (G.) truncatulinoides Pachytheca (P. 405 below; see also reference note no. 64), the "thickened wall" of G. (T.) tosaensis tosaensis consists of a felted mass of lath like sclerites which has no obviously euhedral crystals amongst its felted mass of sclerites. The felted mass of lath like sclerites forms a sheathlike structure which envelops very nearly all of the test, with the usual exception of the apertural face of the final chamber; although, over the last chamber the sheath like structure is thinner and less well developed. Nevertheless, this sheath like structure is remarkably uniform in structure over the individual specimen, between specimens of the taxon and even between specimens of the three taxa G. (T.) crassaformis ronda, G. (T.) tosaensis tosaensis and G. (G.) truncatulinoides pachytheca. The constancy of the structure of the sheath of felted sclerites between specimens, and within the evolutionary lineage of the three taxa, completely discounts that it is merely due to exogenous thickening by secondary secretion of CaCO3 resultant upon a change of habitat as postulated by BE and others [641. The formation of the sheath like structure may be a result of the proliferation and fusing together of the separate pustules of the wall which are present in many species of the Tertiary Globigerinacea. The nature of the pustules in many taxa of the Globorotaliidae has long been recognised as connected with cytoplasmic processes and this is substantiated from an analysis of their distribution especially in the apertural regions. The ultrastructure of unaltered carinae in Globorotalia (Globorotalia) also seems to consist of a mass of interlocking lath like sclerites but with a much higher degree of organisation and with preferred orientation of the laths; this gives a translucent optical response to the carinal structure which is not seen in the "thickened wall" of G. (T.) tosaensis tosaensis with its probable more randorn structure and "chalky" opaque optical response. Thus, the sheath of randomly orientated, felted mass of sclerites seen in the "thickened forms" of G. (G.) truncatulinoides pachytheca, G. (T.) tosaensis tosaensis and G. (T.) crassaformis ronda is believed to be due to a genetic mechanism and this should be recognised by formal taxonomic distinction at some nomenclatorial level. The writer makes a taxonomic distinction between those forms with discrete and separated pustules, superimposed upon a wall of "normal' structure, from those forms in which the pustules have apparently proliferated and fused together so giving a sheath like structure entirely covering at least a part of the "normal' wall. At present and until more is known of the ultra structures of the pustules in different taxa and until more is known of the ultra structures of the carinae of the Globorotaliidae and the cortex of the Sphaeroidinellinae, the writer employs the lowest formal taxonomic category for the distinction of forms with the "thickened" wall (i.e., those which possess a sheath like structure of randomly orientated lath like sclerites) from those with a "normal" wall with only discrete and well separated pustules. Future research may require that this taxonomic procedure is revised. Reference should be made here to the comments given in reference note nos. 62, 62a and 64 (pp. 415 419). In addition to the differences of wall structure discussed above for G. (T.) tosaensis tosaensis and G. (T.) tosaensis tenuitheca, there are small but significant differences in gross morphology between the two forms. Thus, in G. (T.) tosaensis tosaensis, the chambers as seen in dorsal aspect tend to be longer tangentially (anterior posterior) as compared to their radial breadth than in G. (T.) tosaensis tenuitheca, n. subsp. Further, in tosaensis (s.s.) the dorsal intercameral sutures are more sharply recurved and less deeply incised than they are in tenuitheca. Again, the dorsal surface of the test in tosaensis (s.s.) is a little more inflated than in tenuitheca but, more importantly, the dorsal peripheral margin in tenuitheca is usually sub acute whilst it is more broadly rounded in tosaensis (s.s.). Most of these differences seem to be a reflection of the probably separate ancestry of the two forms. Thus, G. (T.) tosaensis tosaensis appears to develop from G. (T.) crassaformis ronda and to carry through some of the general features of the latter taxon. Ort the other hand, G. (T.) tosaensis tenuitheca appears to develop from G. (T.) crassaformis oceanica and perpetuates many of the general characters of this form. The two evolutions do not seern to be quite synchronous and tenuitheca appears a little earlier than tosaensis (s.s.) so that the latter form first occurs just subsequent to the base of Zone N.21. |
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| Blow (1969): 1962 Globorotalia tosaensis Takayanagi & Saito. - Takayanagi & Saito : p.81 pl. 28, figs. 11-12
1969 Globorotalia (Turborotalia) tosaensis tosaensis Blow. - Blow : p.393 pl. 4, figs. 10-12; pl. 40, figs. 4-7
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| References: | ||||||
Takayanagi,Y. and Saito,T. (1962): Blow,W.H. (1969): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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