Lenticulina gibba

Lenticulina gibba (d’Orbigny, 1839) Pl. 2, figs. 7–8

Cristellaria gibba d’Orbigny, 1839, p. 40, pl. 7, figs. 20–21; Brady, 1884, p. 546, pl. 69, figs. 8–9.

Robulus oblongus Coryell & Rivero, 1940, p. 332, pl. 43, fig. 12.

Robulus gibbus Bermúdez, 1949, p. 126, pl. 7, figs. 53–54.

Lenticulina gibba Barker, 1960, pl. 69, figs. 8–9; Lowry, 1987, p. 168, pl. 9, fig.2; Jones, 1994, p. 81, pl. 69, figs. 8–9; Robertson, 1998, p. 66, pl. 22, fig. 4.

Description: The test wall is calcareous, smooth and finely perforate. The test is planispiral involute and longer than wide; biconvex in side view. A narrow keel surrounds the periphery of the test, becoming narrower along later chambers. There are six to nine chambers in the final whorl. The chambers gradually increase in size toward the terminal chamber. The sutures are flush and slightly curved. The aperture is radiate and terminal.

Remarks: Specimens are moderately sized, measuring 0.5 mm in diameter and 0.75 mm in length. The relative abundance is generally low, forming minor components (<5%) in some of the core samples.

This species appears more elongated and oblong compared to other Lenticulina species in the assemblage. The central boss, from where the test’s curved radial sutures extend, is not as largely developed as many other species. There is a variation in the width of the keel between specimens of this species.

Life strategy: Species of the genus Lenticulina are generally epifaunal (Corliss and Chen, 1988) under oxic (Pezelj et al., 2013 and references therein) to suboxic conditions (Kaiho, 1994). The bathymetric range of Lenticulina gibba is reported as shelf to upper slope (Holbourn et al., 2013).

Global stratigraphic range: This species is documented to be extant and occurs in early Miocene to Recent strata (Holbourn et al., 2013).

Regional occurrence: This study records L. gibba to occur in middle Miocene sediments on the Namibian outer continental shelf, south of the Kunene River mouth (this study). Lowry (1987) recorded this species in surface sediments on the continental shelf off Cape St. Blaize, Mossel Bay, on the southern margin of South Africa.