Afrocymbella nyassae Stone & Wilson & Jovanovska 2022, sp. nov.

Afrocymbella nyassae sp. nov. (LM Figs 32–53, SEM Figs 54–59)

Description:— Valve length 20–30 μm, valve breadth 7–10 μm. Length to breadth ratio: 2.8. Valves distinctly dorsiventral and heteropolar, semirhomboid-lanceolate (Figs 32–59). Dorsal margin distinctly arched, ventral margin with gibbous center portion, though otherwise slightly convex (Fig. 55). Valve apices with rostrate and nearly symmetrical poles (Figs 32–53). Internally, valve apices bear small to indistinguishable pseudosepta (Fig. 59). APF of round poroids present at footpole (Fig. 56), surrounded internally by knobby jointed ridge of silica (white arrow in Fig. 59). Axial area narrow, dorsal margin slightly curved (Figs 32–53, 55). Central area round, slightly asymmetric, wider on dorsal side (Figs 32–53, 54). Single stigmoid present on dorsal side of central nodule, externally circular to transapically elongated (Figs 54, 55), internally elongated slit (Figs 57, 58). Raphe curved and slightly sinusoidal (Figs 54, 55). External proximal raphe ends expanded into small pores dorsally deflected (Figs 54, 55), internally covered by nodular or flap-like silica development (Figs 57, 58). External distal raphe terminal fissures ventrally deflected (Figs 55, 56), internally slightly elevated into small lobed helictoglossa at some distance from valve apices (Figs 57, 59). Striae radiate throughout, uninterruptedly continuing onto valve mantle (Fig. 55), 14–16 in 10 μm at middle; 18 in 10 μm at valve apices. Striae composed of 30–35 lineate to slit-like areolae in 10 μm, internally ellipsoid without velum (Fig. 57).

Type:— REPUBLIC OF MALAWI. Lake Malawi central basin, Core MAL05-1 C, Drive 26E2; mud, sampled at 17–18 cm; composite 83 m depth (corresponding to ~135.5 ka), 11°17’39.6” S 34°26’09.0” E, J. R. Stone, 22 nd May 2006 (holotype designated here, circled specimen ANS-GC17194! = Fig. 39, isotypes circled specimens ANSGC17195!, BM-101978! Cleaned type materials: ANS-GCM 33026.

Registration: https://zoobank.org/NomenclaturalActs/13f4f4e3-74e6-41ba-bd38-a84665cfacd3

Etymology:— The species name ‘ nyassae ’ refers to the type locality, Lake Malawi (aka Lake Nyassa).

Distribution:— To date, Afrocymbella nyassae sp. nov. has only been observed from sediment assemblages of Lake Malawi ranging from ~140 ka to 90 ka in the MAL05-1C drillcore (1C, Fig. 1). It is likely an extinct species, seemingly without extant populations.