pforams@mikrotax - Laeviheterohelix flabelliformis

Citation: Laeviheterohelix flabelliformis Nederbragt 1991

Basionym: Laeviheterohelix flabelliformis

Taxonomic discussion: Laeviheterohelix flabelliformis has been found in rather poorly preserved samples only. All specimens are recrystallized; as a result, details of the wall structure could not be observed. However, the presence of forms which are morphologically intermediate with L. pulchra, as well as the consistent absence of costae, point to a microperforate test (in H. globulosa and Psg. costellifera specimens from the same samples the presence of costae can always be seen).
Laeviheterohelix flabelliformis is a Turonian homeomorph of the Maastrichtian genus Gublerina, from which it morphologically differs in wall structure, as well as in stratigraphic range. For Gublerina, the chamber arrangement is a reason for distinction of a separate genus; the same should apply to L. flabelliformis. However, because of its limited geographic and stratigraphic range, I prefer to assign it for now to the same genus as its probable ancestor L. pulchra.

Laeviheterohelix flabelliformis seems to be an endemic form with a short biostratigraphic range. Its limited range is comparable to that of the approximately coeval Lunatriella spinifera Richer and Worstell, which was described from the Western Interior of the United States (Richer and Worstell 1970a) and later encountered in West African sediments (Petters 1983). Both forms appear to represent morphologic modifications of L. pulchra, which did not become established as a world-wide species. [copied from Chronos database]

Original description: Test biserial throughout, early chambers globular to slightly reniform; adult chambers distinctly reniform, with enlarged apertural flanges separating the widely spaced chambers. Surface smooth, without costae; aperture not observed

Most likely ancestor: Laeviheterohelix pulchra - at confidence level 3 (out of 5). Data source: Nederbragt 1991.

Geological Range:
Last occurrence (top): within M. schneegansi zone (89.91-92.56Ma, top in Turonian stage). Data source: [copied from Chronos database]
First occurrence (base): within H. helvetica zone (92.56-93.52Ma, base in Turonian stage). Data source: [copied from Chronos database]

References:

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

test outline:	Palmate	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:	Narrowly rounded	accessory apertures:	N/A
spiral sutures:	Weakly depressed	umb depth:	N/A	wall texture:	Smooth	shell porosity:	Microperforate: <1µm
umbilical or test sutures:	Weakly depressed	final-whorl chambers:	2.0-4.0	N.B. These characters are used for advanced search. N/A - not applicable

Laeviheterohelix flabelliformis

References:

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