Melonis affinis (Reuss, 1851)

Pl. 6, fig. 5

Nonionina affinis Reuss, 1851, p. 72, pl. 5, fig. 32.

Noniona barleeana Williamson, 1858, p. 32, pl. 3, figs. 68–69.

Nonionina crassula Parker & Jones, 1857, p. 14, pl. 11, figs. 5–7.

Nonion barleeanum Cushman, 1930, p. 11, pl. 4, fig. 5.

Melonis barleeanum Loeblich & Tappan, 1988, pl. 696, figs. 5–6; Hermelin, 1989, p. 88, pl. 17, fig. 12; Milker & Schmiedl, 2012, p. 115, fig. 26.11–26.12; Holbourn et al., 2013, p. 354.

Melonis barleeanus Loeblich & Tappan, 1994, p. 159, pl. 347, figs. 1–5.

Melonis affinis Milker et al., 2009, p. 218, pl. 3, fig. 20; Milker and Schmiedl, 2012, p. 115, fig. 26.9–10.

Description: The test wall is calcareous and perforate. The test is planispiral and symmetrical in side view. The periphery of the test is rounded. Up to twelve chambers in the final whorl are separated by smooth, slightly curved sutures. The chamber walls are coarsely perforate and the sutures very finely perforate. The sutures radiate from the umbilical region, becoming thinner toward the test margin. The chambers gradually increase in size toward the apertural end. The aperture is an interio-marginal slit.

Remarks: The relative abundances of Melonis affinis decrease toward the deeper cores, forming minor (<10%) to trace (<1%) components in the samples of all three cores. The tests are moderate in size, measuring up to 0.5 mm in diameter.

Life strategy: This species lives unattached in mostly infaunal and muddy substrates (Murray, 1991). M. affinis is most abundant in oxic conditions, but is also tolerant of dysoxic and suboxic conditions (Kaiho, 1994; Murray, 2006). The species is also associated with the nitrate reduction zone (Fontanier et al., 2002) on the shelf to slope (Holbourn et al., 2013).

Global stratigraphic range: This species occurs from the Oligocene to Recent (Holbourn et al., 2013).

Regional occurrence: Melonis affinis is recorded to occur in middle Miocene sediments on the outer continental shelf of Namibia, south of the Kunene River mouth (this study) and in moderate abundances during the late Miocene to Pliocene along the slope of northern Namibia to the southwestern slope of South Africa (Wefer et al., 1998). Wefer et al. (1998) recorded the occurrence of M. affinis (= M. barleeanus) only in low to moderate (<2 to <20%) abundances along the slope off the Walvis Ridge during the Pleistocene.