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Microhedbergella rischi


Classification: pf_mesozoic -> Hedbergellidae -> Microhedbergella -> Microhedbergella rischi
Sister taxa: M. albiana, M. intermedia, M. miniglobularis, M. praeplanispira, M. pseudodelrioensis, M. pseudoplanispira, M. pseudotrocoidea, M. renilaevis, M. rischi, M. sp.

Taxonomy

Citation: Microhedbergella rischi (Moullade, 1974)
Rank: Species
Basionym: Hedbergella rischi

Type images:

Original description: Translated from French [Described under the name Hedbergella (Hedbergella) sp. aff. infracretacea (Glaessner, 1937) by Moullade, 1966 and renamed by him H. rischi in 1974]: "Hedbergella sp. aff. infracretacea usually displays a more noticeable increase in the height of the spire, hence a slightly more important last chamber compared to the preceding ones. In profile view, the test seems to have a slightly less thick section. The ventral side is umbilicate as opposed to H. infracretacea which is devoid of umbilicus. In the evolved well-characterized forms, we can see a noticeable extension of the aperture towards the periphery, clearly reaching the dorsal edge: the coiling, however, remains asymmetrical, does not become planispiral. Occasionally a slight distortion of the trochospire has also been observed, the arrangement of the last chambers appearing to be less even than in H. infracretacea."

Entries in the Catalog of original descriptions: Hedbergella rischi


Emended description: [Huber & Leckie, 2011, p. 79]: Test wall microperforate in older part of its evolutionary range (pore diameters 0.7 to 1.0 microns), finely perforate in its younger range (pore diameter 1.0 to 2.0 microns), with widely scattered and randomly distributed pores, wall surface smooth. Test small, coiled in a low to moderate trochospire, equatorial periphery rounded, weakly to moderately lobate in equatorial view; chambers subglobular to globular, increasing moderately in size, 11 to 13 coiled in 2 to 2.5 whorls with 4.75 to 6, rarely 6.5 in the final whorl, never with kummerform chambers, penultimate:antepenultimate chamber length ratio averaging 1.3, sutures moderately depressed, radial on umbilical side, radial to slightly oblique on spiral side; umbilicus moderately deep and narrow, comprising 16 to 26% of test diameter; aperture an extraumbilical low arch that extends from near equatorial peripheral margin nearly to the umbilicus, bordered by a narrow lip that may broaden to a flap in final chamber, with weakly developed relict apertural lips surrounding the umbilicus. Test size generally ranges 120 to 180 microns. [copied from Chronos database]

Geological Range:
Last occurrence (top): within P. ticinensis zone (101.92-103.94Ma, top in Albian stage). Data source: [copied from Chronos database]
First occurrence (base): at base of M. rischi zone (0% up, 113Ma, in Albian stage). Data source: zonal marker (from Timescale Creator)

Plot of range and occurrence data:

Character matrix

test outline:Lobatechamber arrangement:Trochospiraledge view:Spiroconvexaperture:Umbilical-extraumbilical
sp chamber shape:Globularcoiling axis:Lowperiphery:N/Aaperture border:Thin lip
umb chbr shape:Globularumbilicus:Narrowperiph margin shape:Broadly roundedaccessory apertures:Relict
spiral sutures:Strongly depressedumb depth:Deepwall texture:Smoothshell porosity:Microperforate: <1µm
umbilical or test sutures:Strongly depressedfinal-whorl chambers:5.0-6.0 N.B. These characters are used for advanced search. N/A - not applicable

References:

Bellier, J. P. & Moullade, M. (2002). Lower Cretaceous planktonic foraminiferal biostratigraphy of the Western North Atlantic (ODP Leg 171b), and taxonomic clarification of key index species. Revue de Micropaléontologie. 45(1): 9-26. gs

Huber, B. T. & Leckie, R. M. (2011). Planktic foraminiferal species turnover across deep-sea Aptian/Albian boundary sections. Journal of Foraminiferal Research. 41: 53-95. gs

Moullade, M. (1974). Zones de Foraminiferes du Cretace inferieur mesogeen. Comptes Rendus Hebdomadaires des Séances de l'Académie des Sciences, Paris. 278: 1813-1816. gs


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Microhedbergella rischi compiled by the pforams@mikrotax project team viewed: 25-10-2020

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Short stable page link: http://mikrotax.org/pforams/index.php?id=110355 Go to Archive.is to create a permanent copy of this page - citation notes



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