Trilobatus bisphericus ( Todd, 1954 )

Bergh, Eugene W. & Compton, John S., 2022, Taxonomy of Middle Miocene foraminifera from the northern Namibian continental shelf, Zootaxa 5091 (1), pp. 1-55 : 33-34

Trilobatus bisphericus ( Todd, 1954)

Pl. 8, figs. 1–2

Globigerinoides bisphericus Todd, 1954, p. 681 , pl. 1, fig.1; Reed, 1965, p. 83, pl. 15, fig. 1–2; Bolli et al., 1985, p. 199, pl. 24, fig.8; Kender et al., 2008, p. 520, pl. 27, figs. 5, 8.

Globigerinoides sicanus Kennett & Srinivasan, 1983, p. 62 , pl. 13, fig. 4–6.

Description: The wall surface is macroperforate and cancellate. The test is rounded and circular in cross section. The three to four chambers in the final whorl are globular in shape. The larger chamber envelops earlier chambers, hiding the umbilicus. The sutures are strongly depressed. Secondary apertures form along deep sutures.

Remarks: The relative abundances of T. bisphericus are trace (<1%) in samples of all three cores. The tests are small, measuring 0.3 mm in diameter.

Bolli et al. (1985) note Trilobatus trilobus (previously Globigerinoides trilobus ) to be ancestral to T. bisphericus .

Environmental preferences: This species is recorded to be adapted to warm waters ( Bicchi et al., 2003), as well as being a cosmopolitan species ( BouDagher-Fadel, 2015).

Global stratigraphic range: T. bisphericus is an indicator species of the early to middle Miocene – Burdigalian to Langhian ( Kennett & Srinivasan, 1983; Bolli et al., 1985; BouDagher-Fadel, 2015).

Regional occurrence: This species is recorded to occur in middle Miocene strata in the Congo Basin ( Kender et al., 2008) to the northern Namibian outer continental shelf, south of the Kunene River mouth (this study).