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| | | Hillsella hillsi Georgescu 2008 |
Current identification:
Diagnosis:Hedbergellid with cancellate test wall and ornamented with scattered pustules. Description:Test very low trochospiral with globular chambers. The last-formed chamber can be slightly radially elongate (Pl. 1:2a, Pl. 2:3c). Sutures are distinct and depressed. Periphery is broadly rounded and without imperforate peripheral band or keels. Aperture is in the shape of medium-high to high arch, peripheral-extraumbilical to peripheral in position, and bordered by an imperfo- rate lip. Relict apertures are present in the shallow and medium-wide umbilical area. Chamber surface is orna- mented with scattered, small-sized pustules. Test wall is calcareous, hyaline, macroperforate, and cancellate. Remarks:The cancellate test wall in Hillsella n. g. has a general resemblance to that of Favusella Michael 1972, and Ascoliella Banner and Desai 1988, which are described as reticulate. The reticulate ornamentation in Favusella and Ascoliella consists of a network of ridges, which are fused to result in a honeycomblike network. Pores, which are 0.8 to 1.1 µm in diameter, are situated in the polygonal or subpolygonal areas enclosed by the network ridges. There are several perforations (3 to 12) present within each of the enclosed areas that form the reticulate ornamentation. By contrast, Hillsella n. g. has pustulose ornamentation, and the general “reticulate” appearance of the test is given by the cancellate test, in which the perforation diameter ranges between 3.1 and 4.2 µm. The irregularly reticulate ornamentation recently described in the upper Campanian–Maastrichtian serial planktonic genus Braunella Georgescu, 2007 (Family Heterohelicidae Cushman 1927) should not be considered similar to either the reticulate or cancellate one from the trochospiral tests (Georgescu, 2007a). The irregularly developed reticulate network in Braunella is the result of partial merging between adjacent costae (Fig.3:2) (Georgescu, 2007b). Chamber surface with fused ridges surrounding each larger pore is developed in another trochospiral genus of the late Albian, namely Biticinella Sigal, 1956. In the case of this genus with smooth chamber surface, the fused ridges apparently result from the thickening of the test wall (Fig. 3:1). Species included Hillsella hillsi nov. sp. Phylogenetic relationships:The ancestor of Hillsella n. g. is unknown. The cancellate test wall and large and dense perforations differentiate this genus from any other known hedbergellid taxon of the middle Cenomanian–Maastrichtian stratigraphic interval. It is unclear at present if Hillsella evolved either from a smooth species of Hedbergella through the direct development of a cancellate test wall, or from a pustulose species through a major change in test ornamentation (i.e., adjustments in pustule size and density) in parallel with a change of the test wall from simple to cancellate and an increase in perforation size. However, the general features of the test, such as chamber shape, position of the main aperture, and the nature of periapertural structures (i.e., imperforate lip) indicate that Hillsella belongs to Subfamily Hedbergellinae Loeblich and Tappan 1961.
Original Description
Etymology:
Extra details from original publication
Georgescu, M. D. (2008b). A new planktonic foraminiferal taxon of the Family Hedbergellidae Loeblich and Tappan 1961 from the Upper Cretaceous (Upper Turonian-Coniacian) of the Caribbean region. Israel Journal of Earth Sciences. 57: 55-63. gsReferences:
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Hillsella compiled by the pforams@mikrotax project team viewed: 20-1-2025
Short stable page link: https://mikrotax.org/pforams/index.php?id=131806 Go to Archive.is to create a permanent copy of this page - citation notes |
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