Marginulina obesa Cushman, 1923a

Bergh, Eugene W. & Compton, John S., 2022, Taxonomy of Middle Miocene foraminifera from the northern Namibian continental shelf, Zootaxa 5091 (1), pp. 1-55 : 19

Marginulina obesa Cushman, 1923a

Pl. 3, figs. 8–9; Pl. 4, fig. 1

Marginulina glabra Brady, 1884, p. 527 , pl. 65, figs. 5–7; Flint, 1899, p. 133, pl. 60, fig. 1.

Marginulina glabra var. obesa Cushman, 1923a , p. 128, pl. 37, fig. 1.

Marginulina obesa Barker, 1960 , pl. 65, figs. 5–6; LeRoy & Levinson, 1974, p. 8, pl. 4, fig. 3–4; Lowry, 1987, p. 174, pl. 9, fig. 12; Jones, 1994, p. 77, pl. 65, figs. 5–6.

Description: The test wall is calcareous and smooth. The test is elongate, circular in cross-section, initially curved, becoming rectilinear in the later stage. Three inflated chambers increase in size towards the terminal end. The chambers are separated by straight and slightly depressed sutures. The aperture is terminal and radiate.

Remarks: The relative abundance of this species is generally low, forming trace components (<1%) in some of the samples of core 2670. The length of the tests in LeRoy & Levinson (1974) is reported to be 1 mm and a diameter of 0.62 mm. The tests in this study are slightly smaller, measuring up to 0.4 mm in cross section diameter and 0.7 mm in length.

Marginulina glabra has been synonymised with Marginulina obesa (e.g., Holbourn et al., 2013), based on similar descriptions between Terquem (1866), Brady (1884) and Cushman (1923a). Brady (1884) does not distinguish between the variations within the species, where the length and stoutness is concerned. The test should remain inflated and the final chamber as large as at least one third of the test. Confusion might arise with M. glabra that is also described by Parker et al. (1865), but the test of that species is not inflated, is thin and is more elongated, compared to M. obesa and M. glabra described in Brady (1884). M. glabra is now not accepted as a species name and the more elongated form described in Parker et al. (1865) should be synonymised with M. similis in d’Orbigny (1846). The terminal chamber in M. similis is also much more reduced, approximately a quarter in size, compared to the more inflated M. obesa .

Life strategy: The bathymetric distribution of M. obesa is recorded as slope to abyssal ( Holbourn et al., 2013). Species of the genus Marginulina are generally shallow-infaunal in environments with variable conditions of low ( Bernhard, 1986) to high oxygen ( Milker & Schmiedl, 2012).

Global stratigraphic range: This species occurs from the Miocene to Recent ( Jones, 1994).

Regional occurrence: M. obesa is documented to occur in middle Miocene sediments on the Namibian outer continental shelf, south of the Kunene River mouth (this study) and in surface sediments along the south coast of South Africa ( Lowry, 1987).