Trilobatus subsacculifer ( Cita, Premoli Silva and Rossi, 1965 )

Bergh, Eugene W. & Compton, John S., 2022, Taxonomy of Middle Miocene foraminifera from the northern Namibian continental shelf, Zootaxa 5091 (1), pp. 1-55 : 35

Trilobatus subsacculifer ( Cita, Premoli Silva and Rossi, 1965)

Pl. 8, figs. 5–6

Globigerinoides sacculifer subsacculifer Cita, Premoli Silva and Rossi, 1965, p. 268 , pl. 31, figs. 3a–c.

Globigerinoides subsacculifer Spezzaferri 1994, p. 38 , pl. 13, figs. 4a–c; Spezzaferri et al., 2018b, p. 298, pl. 9.13, figs. 1–20.

Description: The test surface is macroperforate. The test is trochospiral, globular and semi-circular in outline. There are four chambers in the final whorl, with the three basal chambers underneath the primary aperture separated by deep incised sutures. These basal chambers are overarched by a chamber that is finer in texture and shaped at a rounded angle to one side. The final chamber is lobulate in shape and is not always the largest chamber. The penultimate chamber is often the largest. The primary aperture forms a low arch above the three basal chambers on the apertural side. The apertural arch has a thin finely punctate layer and is often not as coarsely perforated as the rest of the test. Several supplementary apertures form on the spiral side of the test along sutures.

Remarks: The relative abundances of T. subsacculifer form a minor component (<10%) of the planktic foraminiferal assemblage in all three cores. The abundances are highest below the Mio-Pliocene contact. The tests are relatively small to moderate in size, measuring up to 0.4 mm in diameter.

This species resembles Trilobatus sacculifer , but the last chamber might only be slightly pronounced and less sac-like compared to T. sacculifer . Tests of T. subsacculifer are also generally smaller than T. sacculifer , with a smaller arched primary aperture ( Spezzaferri et al., 2018b).

Global stratigraphic range: The stratigraphic range for T. subsacculifer is in the Miocene, from the Aquitanian to Messinian ( Spezzaferri et al., 2018b).

Regional occurrence: This species is recorded in middle Miocene-aged sediments of the northern Namibian outer continental shelf, south of the Kunene River mouth (this study) .