Afrocymbella nyassae, Stone & Wilson & Jovanovska, 2022

Stone, Jeffery R., Wilson, Mallory C. & Jovanovska, Elena, 2022, The genus Afrocymbella (Bacillariophyceae) from lakes Malawi and Tanganyika, with description of new fossil and extant species, Phytotaxa 556 (1), pp. 21-48 : 25

publication ID

https://doi.org/ 10.11646/phytotaxa.556.1.3

DOI

https://doi.org/10.5281/zenodo.6951977

persistent identifier

https://treatment.plazi.org/id/03AC87E9-455A-FFA6-FF28-FB71FD9B0223

treatment provided by

Plazi

scientific name

Afrocymbella nyassae
status

sp. nov.

Afrocymbella nyassae sp. nov. (LM Figs 32–53 View FIGURES 32–53 , SEM Figs 54–59 View FIGURES 54–56 View FIGURES 57–59 )

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 View FIGURES 32–53 View FIGURES 54–56 View FIGURES 57–59 ). Dorsal margin distinctly arched, ventral margin with gibbous center portion, though otherwise slightly convex ( Fig. 55 View FIGURES 54–56 ). Valve apices with rostrate and nearly symmetrical poles ( Figs 32–53 View FIGURES 32–53 ). Internally, valve apices bear small to indistinguishable pseudosepta ( Fig. 59 View FIGURES 57–59 ). APF of round poroids present at footpole ( Fig. 56 View FIGURES 54–56 ), surrounded internally by knobby jointed ridge of silica (white arrow in Fig. 59 View FIGURES 57–59 ). Axial area narrow, dorsal margin slightly curved ( Figs 32–53 View FIGURES 32–53 , 55 View FIGURES 54–56 ). Central area round, slightly asymmetric, wider on dorsal side ( Figs 32–53 View FIGURES 32–53 , 54 View FIGURES 54–56 ). Single stigmoid present on dorsal side of central nodule, externally circular to transapically elongated ( Figs 54, 55 View FIGURES 54–56 ), internally elongated slit ( Figs 57, 58 View FIGURES 57–59 ). Raphe curved and slightly sinusoidal ( Figs 54, 55 View FIGURES 54–56 ). External proximal raphe ends expanded into small pores dorsally deflected ( Figs 54, 55 View FIGURES 54–56 ), internally covered by nodular or flap-like silica development ( Figs 57, 58 View FIGURES 57–59 ). External distal raphe terminal fissures ventrally deflected ( Figs 55, 56 View FIGURES 54–56 ), internally slightly elevated into small lobed helictoglossa at some distance from valve apices ( Figs 57, 59 View FIGURES 57–59 ). Striae radiate throughout, uninterruptedly continuing onto valve mantle ( Fig. 55 View FIGURES 54–56 ), 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 View FIGURES 57–59 ).

Type:— REPUBLIC OF MALAWI. Lake Malawi central basin, Core MAL05-1 View Materials 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 View FIGURES 32–53 , isotypes circled specimens ANSGC17195 !, BM-101978! Cleaned type materials: ANS-GCM 33026. GoogleMaps

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 View FIGURE 1 ). It is likely an extinct species, seemingly without extant populations.

R

Departamento de Geologia, Universidad de Chile