Petroplacus pantocsekii (Wislouch & Kolbe) Vishnyakov, 2019

Vishnyakov, Vasily S., 2019, Notes on the genus Petroplacus (Bacillariophyceae) with new nomenclature transfer, Phytotaxa 391 (3), pp. 225-232 : 228

Petroplacus pantocsekii (Wislouch & Kolbe) Vishnyakov , comb. & stat. nov. ( Figs 1–26 )

Basionym: — Navicula platystoma var. pantocsekii Wislouch & Kolbe 1916 , Journal de Microbiologie [Журналъ микробiологiи], 3(3–4): 266, 449, fig. 3: 7.

Heterotypic synonym: — Navicula platystoma var. pantocsekii [pantocseki] Gallik 1930, Folia Cryptogamica, 1(2): 743, fig. 19: 5, 6, nom. illeg., syn. nov.

Lectotype (designated here): — Fig. 3 : 7 in Wislouch & Kolbe 1916.

Examined specimens: — RUSSIA. Yaroslavl Region, Rybinsk district:Mologa station, 58°12.472′N, 38°27.336′E, 14 m depth, the topmost 2.5 cm of sandy silt, pH 7.52, 7 August 2016. Coll. O. Makarova. Slide no. V195 IBIW. Breitovo district: Breitovo station, the Mologa riverbed near Breitovo village, 58°19.198′N, 37°56.577′E, 11 m depth, the topmost 2.5 cm of clayey silt, pH 7.52, 11 October 2016. Coll. T. Zaikina. Slide no. V223 IBIW. Rybinsk district: Mologa station, the Volga riverbed near the flooded Mologa town, 58°12.472′N, 38°27.336′E, 13 m depth, the topmost 2.5 cm of sandy silt, pH 7.52, 25 October 2016. Coll. T. Zaikina. Slide no. V227 IBIW.

Figures

FIGURES 1–15. Petroplacus pantocsekii, LM. 1–6, 8–15. Specimens from Rybinsk reservoir showing the size diminution series. 7. The figure designated as lectotype depicting specimen from original material, Lake Onega, phot. by Wislouch and Kolbe (1916).

FIGURES 16–22. Petroplacus pantocsekii, SEM. 16. External valve view showing raphe branches with expanded central pores and straight terminal fissures unilaterally deflected (arrows). 17. Internal valve view showing thickened raphe sternum and central area. 18. Detail of external view of the valve center showing transversely elongated central area, proximal raphe endings with expanded central pores, and radial pattern of uniseriate striae; intercalary stria is visible (arrow). 19. Internal valve view showing thickened central nodule, straight proximal raphe endings (black arrows) connected by longitudinal depression (white arrow). 20–22. External proximal raphe endings lying in spatulate grooves and accompanied by lips-like structure.

FIGURES 23–26. Petroplacus pantocsekii, SEM. 23, 24. Details of internal valve view showing thickened raphe sternum. 24. Distal raphe ending with elongated helictoglossa (arrow). 25, 26. Internal striae arrangement in intact (25) and corroded (26) specimens showing moniliform ‘flaps’ coalesced together and sunk into the shallowed canals between virgae.