Trilobatus immaturus ( LeRoy, 1939 )

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

Trilobatus immaturus ( LeRoy, 1939)

Pl. 8, fig. 3

Globigerinoides sacculifer var. immaturus LeRoy, 1939, p. 263 , pl. 3, figs. 19–21.

Globigerinoides quadrilobatus Banner & Blow, 1960, p. 17 , pl. 4, figs 3a–b.

Globigerinoides trilobus immaturus Bolli et al., 1985 , figs. 20.14.

Globigerinoides trilobus var. immatura Jenkins, 1960, p. 354 , pl. 2, fig. 7a–c.

Globigerinoides immaturus Kennett & Srinivasan, 1983, p. 64 , pl. 10, fig. 3; pl. 13, fig. 7–9; Kender et al., 2008, p. 520. pl. 27, fig. 3.

Trilobatus immaturus Spezzaferri et al., 2018b, p. 289 , pl. 9.9, figs. 1–2; Poole and Wade, 2019, 2003, figs. 6P, 7A–K, 17B, 17F.

Description: The test surface is macroperforate and cancellate-spinose. The test is trochospiral, globular and semi-circular in cross section. The chambers are rounded with 2.5 basal chambers separated by deep incised sutures, overarched by a large chamber that has the width of all three lower chambers. A total of 3 to 3.5 chambers encompasses the final whorl of the test. The primary aperture forms a low arch above the basal chambers on the umbilical side. The middle basal chamber is larger than the two side chambers. Supplementary apertures form on the spiral side of the test along sutures.

Remarks: This species was found to be abundant in some of the samples (<80%). The relative abundance of T. immaturus is higher in deeper cores (2658 and 2670). Tests are moderate in size, measuring up to 0.45 mm in diameter.

Trilobatus immaturus (previously Globigerinoides trilobus immaturus ) is distinguished from Trilobatus trilobus by its smaller final chamber (Bolli, 1957). Bolli et al. (1985) identified Gs. quadrilobatus as being the synonym for T. immaturus .

Environmental preferences: Trilobatus immaturus is considered to be a warm water species ( Reeder et al., 1998).

Global stratigraphic range: This species has been recorded to occur from the early Miocene to Recent ( Kennett & Srinivasan, 1983).

Regional occurrence: Trilobatus immaturus occurs in Miocene-aged strata of the Congo Basin ( Kender et al., 2008) and northern Namibian continental shelf, south of the Kunene River mouth (this study).