pforams@mikrotax - Planohedbergella circularis pforams@mikrotax - Planohedbergella circularis

Planohedbergella circularis


Classification: pf_mesozoic -> Globigerinelloididae -> Planohedbergella -> Planohedbergella circularis
Sister taxa: P. aspera, P. circularis, P. escheri, P. impensa, P. messinae, P. multispina, P. prairiehillensis, P. subcarinata, P. ultramicra, P. yaucoensis

Taxonomy

Citation: Planohedbergella circularis Huber & Petrizzo, in Huber et al. 2022
taxonomic rank: Species
Basionym: Planohedbergella circularis Huber & Petrizzo, in Huber et al. 2022
Taxonomic discussion: This species has a very distinctive ontogenetic morphology. The proloculus diameter averages 17 m, which is the middle range compared to the other planispiral species, and it is surrounded by 6–8 chambers in the initial whorl. Throughout ontogeny the chamber expansion rate is very slow, with a significant reduction in the final whorl such that the last several chambers are nearly equidimensional, and the final chamber is often kummerform. The 8.0–9.5 chambers in the final whorl and the UD:TD ratio are in the upper range compared to the other Albian–Maastrichtian planispiral species measured.

Type images:

Entries in the Catalog of original descriptions: Planohedbergella circularis

Distinguishing features:
Parent taxon (Planohedbergella):

Test planispiral throughout, biumbilicate, peripheral margin rounded to acute; wall micro-finely perforate and muricate throughout; coiling involute to evolute, chambers globular to axially compressed; may be uniapertural or biapertural with bordering lip. Differs from Laeviella by having a muricate rather than smooth test surface; differs from Polycamerella by lacking any infolding of the test wall along the sutural margin of biapertural portici.


This taxon:
Differs from other Planohedbergella species as it has more evolute coiling, greater final whorl and total number of chambers that increase more slowly in size and are nearly equidimensional in the final whorl, its more circular peripheral outline, and its wider umbilicus;
Differs from species included in Laeviella by its coarsely pustulose wall surface texture;
Differs from Plh. impensa by its more rounded peripheral margin, more even distribution of moderate to coarse pustules on the test surface, and absence of costellae on the equatorial periphery;
Differs from Po. tardata n. sp. by its larger size, more lobate peripheral outline and slower chamber expansion rate in the final whorl.


Morphology:
Test planispirally coiled, biumbilicate, evolute (UD:TD ratio average 0.37), with some specimens becoming uncoiled, moderately lobate and circular in outline with a rounded peripheral margin, symmetrical in edge view, uniapertural forms much more common than biapertural forms; chambers globular, moderately inflated, enlarging very slowly in size (y = 0.092x + 2.04), from 19–23 total number of chambers in adult specimens usually coiled in 2.5 whorls, 8.0 to 9.5 in final whorl with a reduction in the chamber expansion rate in such that the last several final whorl chambers are nearly equidimensional, kummerform chambers relatively common (UCL:PCL ratio average = 1.02; sutures radial, moderately depressed; interiomarginal aperture centered on equatorial margin with a circular to semicircular arch extending 1⁄4 to ? up final chamber face and part way toward umbilicus, bordered by a narrow lip, while bipartite apertures are extraumbilical circular openings that are also bordered by a narrow lip; relict apertures surround the umbilicus and are particularly visible in final several chambers.

Wall type:
Finely perforate with wall pores averaging 1.8 m in diameter, surface with evenly scattered moderate to coarse, sharply pointed pustules.

Size:
Holotype USNM 770991 maximum diameter 315 m, maximum breadth 139 m; paratype USNM maximum diameter 289 m, maximum breadth 158 m; paratype USNM 770993 maximum breadth 271 m, maximum breadth 139 m; maximum diameter of hypotypes ranges from 256–403 m.

Character matrix
test outline:Circularchamber arrangement:Planispiraledge view:Hourglassaperture:Equatorial
sp chamber shape:-coiling axis:N/Aperiphery:N/Aaperture border:Thin lip
umb chbr shape:-umbilicus:Wideperiph margin shape:Moderately roundedaccessory apertures:Relict
spiral sutures:Moderately depressedumb depth:Shallowwall texture:Moderately pustuloseshell porosity:Finely Perforate: 1-2.5µm
umbilical or test sutures:Moderately depressedfinal-whorl chambers:8-9.5 N.B. These characters are used for advanced search. N/A - not applicable

Most likely ancestor: Planohedbergella yaucoensis - at confidence level 2 (out of 5). Data source: Huber et al. 2022 fig. 2.

Geological Range:
Notes: Oldest occurrence recorded in upper Campanian Radotruncana calcarata Zone at Blake Nose ODP Sample 1050C-18R-CC (e.g., Pl. 10, Figs. 7a–7b), ranges through upper Maastrichtian Plummerita hantkeninoides Zone at ODP Hole 1049C (Huber et al., in press).
Last occurrence (top): within P. hantkeninoides zone (66.04-66.39Ma, top in Maastrichtian stage). Data source: Huber et al 2022
First occurrence (base): within R. calcarata zone (75.06-75.91Ma, base in Campanian stage). Data source: Huber et al 2022

Plot of range and occurrence data:

References:

Huber, B. T., Petrizzo, M. M. & Falzoni, F. (2022b). Taxonomy and phylogeny of Albian–Maastrichtian planispiral planktonic foraminifera traditionally assigned to Globigerinelloides. Micropaleontology. 68(2): 117-183. gs


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Planohedbergella circularis compiled by the pforams@mikrotax project team viewed: 2-3-2024

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Short stable page link: https://mikrotax.org/pforams/index.php?id=110602 Go to Archive.is to create a permanent copy of this page - citation notes



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