pforams@mikrotax - Laeviheterohelix pulchra

Citation: Laeviheterohelix pulchra (Brotzen, 1936)

Taxonomic discussion: listed under "Guembelina pilchra" [misspelled] in E+M online catalogue.
The wall structure of L. pulchra appears to be ecophenotypic. Smooth specimens are found in high latitude localities, specimens with pore mounds are present in Tethyan sections. "Haynes et al 2015: The paratype of Lv. pulchra illustrated on Figure 25.9 has strongly overlapping reniform chambers and faint pore mounds that are only visible under high magnification (Fig. 25.9c). Pore mounds are a key characteristic of this species and their size is variable, with some becoming large and well-developed (e.g., Fig. 25.7; Georgescu, 2009a, fig. 9). Nederbragt (1989, 1991) suggested that pore mounds are expressed only on smooth-walled individuals that lived in tropical locations, and therefore, were considered a poor characteristic to define a species. Recent studies, however, show that smooth-walled forms with well-developed pore mounds occur at high latitude sites such as the Falkland Plateau (DSDP Site 511; Fig. 25.7; Bice et al., 2003; Georgescu, 2009a). Steineckia steinecki Georgescu, 2009a, differs from Lv. pulchra in having larger pore mounds, no periapertural pustulose area, and no evidence of vestigial costae (Georgescu, 2009b). The paratype of Lv. pulchra and two other specimens illustrated here (Figs. 25.7 - 25.9) lack both vestigial costae and periapertural pustulose areas. They also show a large range of variability in terms of pore mound size, suggesting that these features are not suitable to characterize a separate species; therefore, we consider St. steinecki to be a junior synonym of Lv. pulchra." [copied from Chronos database]

Original description: Test biserial, surface smooth or with pore mounds. Periphery rounded, chambers reniform. Aperture bordered by elongate flanges, which extend to the opposite periphery. Relict flanges of preceding chambers are visible along the edges of the test.

Geological Range:
Last occurrence (top): within R. calcarata zone (75.71-76.18Ma, top in Campanian stage). Data source: [copied from Chronos database]
First occurrence (base): within M. schneegansi zone (89.91-92.56Ma, base in Turonian stage). Data source: [copied from Chronos database]

References:

Brotzen, F. (1936b). Foraminiferen aus dem Schwedischen Untersten Senon von Eriksdal in Schonen. Sveriges Geologiska Undersökning, Series C. 1-206. gs

Nederbragt, A. J. (1989b). Maastrichtian Heterohelicidae (Planktonic Foraminifera) from the North West Atlantic. Journal of Micropalaeontology. 8(2): 183-206. gs

Nederbragt, A. J. (1991). Late Cretaceous biostratigraphy and development of Heterohelicidae (planktic foraminifera). Micropaleontology. 37: 329-372. gs

Pessagno, E. A. (1967). Upper Cretaceous planktonic foraminifera from the western Gulf Coastal Plain. Palaeontographica Americana. 5: 245-445. gs

test outline:	Subtriangular	chamber arrangement:	Biserial	edge view:	Compressed	aperture:	Interiomarginal
sp chamber shape:	Reniform	coiling axis:	N/A	periphery:	N/A	aperture border:	Thin flange
umb chbr shape:	Reniform	umbilicus:	N/A	periph margin shape:	Moderately rounded	accessory apertures:	None
spiral sutures:	Moderately depressed	umb depth:	N/A	wall texture:	Pore mounds	shell porosity:	Finely Perforate: 1-2.5µm
umbilical or test sutures:	Moderately depressed	final-whorl chambers:	2.0-2.0	N.B. These characters are used for advanced search. N/A - not applicable

Laeviheterohelix pulchra

References:

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