CATALOG OF ORIGINAL DESCRIPTIONS: Helvetoglobotruncana microhelvetica Huber & Petrizzo, in Huber et al. 2017

This page provides data from the catalog of type descriptions. The catalog is sorted alphabetically. Use the current identification link to go back to the main database.


Higher levels: pf_cat -> H -> Helvetoglobotruncana -> Helvetoglobotruncana microhelvetica
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Helvetoglobotruncana microhelvetica

Citation: Helvetoglobotruncana microhelvetica Huber & Petrizzo, in Huber et al. 2017
Rank: Species
Type locality: TDP 31 (-10.028N; 39.637E), Lindi area, Tanzania
Type age: upper H. helvetica Zone, Turonian
Type sample and level: Sample TDP 31-28-1, 5–25 cm (46.25 meters below surface)
Holotype Repository: Washington; USNM
Type & figured specimens: Holotype USNM 637700 (Pl. 5, Fig. 1) and paratypes USNM 637701– 637702 (Pl. 5, Figs. 2–3)

Current identification/main database link: Helvetoglobotruncana microhelvetica Huber & Petrizzo, in Huber et al. 2017


Original Description
Test small, inequally biconvex, with a maximum diameter of 200–270 μm and maximum breadth 100 to 130 μm, normal perforate (pore size 1.2 to 2.4 μm), nearly planoconvex, subcircular in equatorial outline; equatorial periphery weakly lobate; peripheral margin imperforate except final chamber, which may or may not be perforate; 12–14 chambers in adult tests increase gradually in size as added, with 5–6 in the final whorl; umbilical chambers inflated, chamber surfaces with randomly scattered, fine to moderate-sized pustules, umblical sutures radial and depressed; spiral chambers petaloid, chamber surfaces slightly inflated, with slight convexity toward the peripheral margin, weakly pustulose to smooth with weak alignment of pustules along the peripheral chamber margin, spiral sutures initially depressed and radial, later with weakly aligned pustules; in edge view final chamber offset with respect to spiral coil surface and final chamber face is slightly concave and angled backwards from the peripheral margin; aperture a circular arch that is mostly extra-umbilical in position and bordered by a narrow lip.

Size: Maximum test diameter: holotype 212 μm, illustrated paratype and hypotypes 209 to 264μm; maximum breadth: holotype 125 μm, illustrated paratype and hypotypes 97 to 128 μm.

Etymology: Prefix “micro” used with helvetica to reflect its smaller size and close phylogenetic relationship to H. helvetica.

Extra details from original publication
Remarks: This species is distinguished from H. helvetica (Bolli, 1945) by its smaller size, presence of a more weakly developed pustulose keel on the peripheral margin, greater convexity of the dorsal chambers surfaces, and a smaller, more circular umbilical-extraumbilical aperture. The maximum test diameter of H. microhelvetica mostly ranges between 210 and 280 μm whereas that of H. helvetica mostly ranges from 350 – 600 μm. Transitional forms between these two species (e. g., Huber and Petrizzo 2014, Fig. 7a–c) occur in some samples.

Phylogenetic relationships. Similarity to H. helvetica suggest they are closely related, but presence of an unconformity that truncates the lower range of both species prevents determination of which is the ancestral species.

Stratigraphic range. Restricted to the late early through middle Turonian H. helvetica Zone.

Geographic distribution. Identified at all Tanzanian Drilling Project boreholes that recovered sediments from the H. helvetica Zone but has not been found at any other location outside Tanzania.

References:

Huber, B. T., Petrizzo, M. R., Watkins, D. K., Haynes, S. J. & MacLeod, K. G. (2017a). Correlation of Turonian continental margin and deep-sea sequences in the subtropical Indian Ocean sediments by integrated planktonic foraminiferal and calcareous nannofossil biostratigraphy. Newsletters on Stratigraphy. 50: 141-185. gs


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Helvetoglobotruncana microhelvetica compiled by the pforams@mikrotax project team viewed: 18-9-2020

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