Catalog - Hendersonites pacificus

CATALOG OF ORIGINAL DESCRIPTIONS: Hendersonites pacificus Georgescu 2011

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 -> Hendersonites -> Hendersonites pacificus
Other pages this level: H. pacificus

Hendersonites pacificus

Citation: Hendersonites pacificus Georgescu 2011
Rank: Species
Type specimens: Holotype: WKB 010079. Paratypes: Eighteen paratypes, WKB 010080-010097.
Type age (chronostrat): Uppermost Santonian-lower Campanian (lower part of the Globotruncanita elevata Biozone equivalent).
Type locality: Mid-Pacific Mountains, equatorial Central Pacific
Type repository: Willi Karl Braun Micropaleontological Collection at the University of Calgary (Calgary, Alberta, Canada)

Current identification:


Original Description

Diagnosis: Hendersonites with simple-ridged test wall and reduced costate ornamentation over the last one to two pairs of chambers.


Description: Test with chambers alternately added with respect to the test axis of growth resulting in biserial arrangement; tests consist of 10 to 16 chambers, which increase gradually in size and overlap at various rates. Chamber growth rate is moderate to high in most specimens, rarely lower in the adult stage; earlier chambers are subglobular, then subrectangular and crescentic in the adult and/or gerontic stages. The test is distinctly compressed in the terminal portion in some specimens resulting in a lanceolate edge view outline. Sutures are often indistinct between the earlier chambers of the test due to the heavy ornamentation and addition of successive layers of calcite; those between the chambers of the last two or three pairs are curved towards the anterior part and depressed. Test periphery with distinct test wall flexure lined by coarse costae, which form a rim-like structure around the test as seen in lateral view. Aperture is a low to medium high arch at the base of the last formed chamber; it is bordered by two symmetrically developed, small and rimmed periapertural flanges. There is a well-developed periapertural pustulose area on top of the chamber and above the aperture. Chamber surface is covered with costae, which are thicker over the earlier chambers and become gradually thinner over the last formed ones; juvenile specimens have costae with variable thickness (4.1–6.5 µm) over all chambers of the test; adult and gerontic specimens have thicker costae over the earlier chambers (7.8–8.5 µm) and those of the last formed chambers are much thinner (2.0–2.7 µm). Some of the thickest costae (6.8–7.5 µm) are developed in the peripheral region. Test wall is simple in juvenile specimens, with relatively small pores (1.1–1.9 µm) and simple-ridged with larger pores (3.2–4.2 µm) in the adult and gerontic individuals. Pores consistently occur between the peripheral costae, rarely disrupting them.


Size:
Dimensions: L = 0.189–0.396 mm, W = 0.125–0.272 mm, W/L = 0.661–0.780, t = 0.072–0.117 mm, t/L = 0.295–0.280. Ranges based on the measurements of the holotype and 14 paratypes.

Etymology:
Species named after the Pacific Ocean, where the type locality is situated.

Extra details from original publication
Remarks: Hendersonites pacificus is the only known Cretaceous planktic foraminiferal species with simple-ridged test wall, which is developed in contrast with the reduction of the costate ornamentation (Fig. 5). This demonstrates that the test ultrastructure and ornamentation are two features with distinct evolution in the Hendersonites branched lineage. The similarities in the general test appearance (i.e., chamber shape, peripheral test wall flexure forming a rim-like structure around the test, etc.) and pore size, test ultrastructure and costae thickness over the earlier portion of the test; indicate that H. pacificus evolved from H. carinata.

Editors' Notes

References:

Georgescu, M. D. (2011a). A new type of test wall in the Late Cretaceous (Late Santonian-Campanian) heterohelicid planktic foraminifera. Revue de Micropaléontologie. 54: 105-114. gs


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Hendersonites pacificus compiled by the pforams@mikrotax project team viewed: 5-12-2022

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