Afrocymbella delphinea, 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 : 29-32

Afrocymbella delphinea sp. nov. (LM Figs 60–80 , SEM Figs 81–86 )

Description:— Valve length 27–45 μm, valve breadth 10.5–13.5 μm. Length to breadth ratio: 3.8. Valves distinctly dorsiventral, and strongly heteropolar, semirhomboid-lanceolate ( Figs 60–86 ). Dorsal margin distinctly arched, ventral margin tumescent ( Figs 60–80 ). Valve apices apiculate-rostrate, with rostrate headpole and protracted footpole, particularly in smaller specimens ( Figs 60–80 ). Internally, valve apices with small to indistinguishable pseudosepta ( Figs 84, 86 ). APF of round poroids present at footpole ( Fig. 83 ), covered internally by knobby jointed ridge of silica ( Fig. 86 ). Axial area narrow, curved, slightly displaced ventrally ( Figs 60–80 ). Central area small, oval-shaped, notably wider on dorsal side and often minimal on ventral side ( Fig. 82 ). Single (rarely 2) distinct stigmoid present on dorsal side of central nodule ( Figs 82 , 84 ), appearing slightly elongated in LM ( Fig. 61 ). From inside, stigmoid opening with elongated slit ( Fig. 85 ). Raphe curved and slightly sinusoidal ( Fig. 81 ). External proximal raphe ends expanded into small pores ( Fig. 82 ). External distal raphe terminal fissures ventrally deflected ( Figs 81, 83 ). Internal proximal raphe ends covered by nodular or flap-like silica development formed by primary side of valve ( Figs 84, 85 ). Internal distal raphe terminal fissures slightly elevated into small lobed helictoglossa at some distance from valve apices ( Fig. 86 ). Striae radiate throughout, but can be slightly radiate-curved in central area, 16–20 in 10 μm. Striae continue uninterrupted onto valve mantle ( Fig. 81 ), composed of 26–32 areolae in 10 μm. External areolae slit-like poroids ( Figs 81, 83 ). Internal areolae ellipsoid without velum ( Fig. 84 ).

Type:— REPUBLIC OF ZAMBIA. Lake Tanganyika , Isanga Bay, at 767 m elevation, rock scrape, 8°39’15.9” S 31°11’31.6” E, E.Jovanovska & P.Hamilton, 7 th September 2018, (holotype designated here, circled specimen ANSGC17196 ! = Fig. 74 , isotypes circled specimens ANS-GC17197!, BM-101979!). Cleaned type materials: ANS-GCM 33027 .

Registration: https://zoobank.org/NomenclaturalActs/6d108e31-d99a-4a74-b574-02f8fbc27ed9

Etymology:— The specific epithet ‘ delphinea ’ relates to the delphine (dolphin-like) outline that characterizes this species.

Distribution:— To date, Afrocymbella delphinea sp. nov. has been observed most commonly as an epilithic species attached on rocks in the littoral zones in the southern sub-basin of Lake Tanganyika. We observed this species at sites from Mpulungu (Mp), Chituta (Ch/Cb), Isanga (Is), and near the Kalambo Falls. We also found this species occurring in samples from Chembe (Cm) in the southern sub-basin of Lake Malawi ( Fig. 1 ).

Figures

FIGURE 1. Map of the lakes Tanganyika and Malawi, showing the sampling locations of modern (red circles) and fossil (cores MAL05- 1C and NPO4-KH1-1K; white circles) specimens used in this study.

FIGURES 60–80. Afrocymbella delphinea sp. nov., LM valve views. 60–63, 65–80. Valves from the type material. Fig. 74. Holotype specimen. Scale bar = 10 μm.

FIGURES 81–83. Afrocymbella delphinea sp. nov., SEM external valve views. 81. View of the whole valve showing raphe structure, and striae continue uninterrupted onto valve mantle. 82. Close view of the mid-valve showing dorsally deflected proximal raphe ends and slightly round to slightly elongated single stigmoid on the dorsal side of slightly elongated central nodule. 83. Detail of valve apex showing the slit-like areolae and APF of round poroids. Scale bars = 10 μm (Fig. 81), 2 μm (Figs 82, 83).

FIGURES 84–86. Afrocymbella delphinea sp. nov., SEM internal valve views. 84. View of the whole valve showing raphe structure and areolae without velum. 85. Detail of mid-valve showing proximal raphe ends covered by flap-like silica development and antler-like intermissio stigmoid. 86. Close view of distal raphe terminal fissure and APF with knobby jointed ridge of silica. Scale bars = 5 μm (Fig. 84), 2 μm (Figs 85–86).