Cocconeis baicalensis (B. V. Skvortzov & K. I. Meyer) B. V. Skvortzov 1946 in

Gogorev, Rinat, Yurchak, Maria, Sokolova, Irina, Glushchenko, Anton & Kulikovskiy, Maxim, 2024, Nomenclature and systematics of two Cocconeis species (Bacillariophyta) from Lake Baikal: Cocconeis baicalensis and Cocconeis skvortzowii, PhytoKeys 247, pp. 219-248 : 219-248

Cocconeis baicalensis (B. V. Skvortzov & K. I. Meyer) B. V. Skvortzov 1946 in Zapiski Kharbinskogo Obshchestva Estestvoispytatelei i Etnografov, 2. Botany: 19, pl. 3, fig. 24; pl. 5, figs 9–11 (as “ baikalensis ” (Skv. et Mey.) Skv.) emend. Gogorev & Yurchak

Cocconeis placentula Ehrenberg var. baicalensis Skvortzov & K. I. Meyer 1928 in Proceedings of the Sungaree River Biological Station 1, 5: 11, pl. 1. fig. 25, earlier homonym of C. placentula var. baikalensis Skvortzov 1937 . Basionym.

≡ Cocconeis placentula Ehrenberg subsp. baicalensis (Skvortzov & K. I. Meyer) Skabichevskij 1977 in Prirodnye kompleksy nizshikh rastenii Zapadnoi Sibiri: 127, fig. 2, 6–8 (with authorship of the basionym “ Skv. ”). Synonym.

Type materials.

Lectotype • (designated here): Baikal, Cape Kotelnikovskiy , No. 318, 30 June 1926 [N 318, “ Kotelnikovi Maiak ”, Aegagrophila , 30 / VI- 26], leg. K. I. Meyer, permanent slide No. 318 a, LE A 0004242 .

Isolectotype • Baikal, Cape Kotelnikovskiy , No. 318, 30 June 1926 [N 318, “ Kotelnikovi Maiak ”, Aegagrophila , 30 / VI- 26], leg. K. I. Meyer, permanent slide No. 318 b, LE A 0004243 .

Epitype • (designated here): figures here represented by Fig. 9 C (Baikal, specimen BL 15645 , leg. A. P. Skabichevsky, 20 July 1965) .

Type locality.

Russia, Lake Baikal, Barguzin Bay, Bay Pestchannaya, Boguchanskaya Gulf, Cape Elokhin, Cape Kotelnikovskiy, Island Bolshoy Ushkaniy, Maloe More, Marituy, Selenga River, Village Guelga.

Description.

LM (n = 56) (Figs 3 – 7 ). Valves broadly elliptical, 11.2–29.2 μm in length (mean 19.4), 8.6–21.5 in breadth (mean 14.6). RV with straight raphe, SV with straight or slightly curved axial area. On RV 20–28 striae in 10 μm (mean 23.4) and 18.5–27.5 areolae in 10 μm of stria (mean 24.5), on SV 22–28 striae in 10 μm (mean 24.3) and 13.0–19.5 areolae in 10 μm of stria (mean 16.6). Length to breadth ratio 1.2–1.5: 1 (mean 1.3: 1).

SEM (n = 74). Valves from subcircular to broadly elliptical, with broadly rounded apices, 11.5–36.7 μm in length (mean 19.1–21.3), 8.7–27.1 in breadth (mean 15.2–17.2). Length to breadth ratio 1.0–1.4: 1 (mean 1.2–1.3: 1). RV and SV very different on structure.

RV (n = 28). Valves concave, with straight raphe and narrow-linear axial area. Striae uniseriate, 21–32 in 10 μm (mean 24.6), weakly radial in valve middle, more radial towards valve apices, interrupted by submarginal hyaline strips and not reached valve margin. Areolae 20–31 in 10 μm of stria (mean 24.8), absent at valve apices. Valve mantle reversed (contra mantle): valve face flat, mantle (or part of it) elevated and opposite directed to the adjacent SV, these two parts (flat and raised) separated from each other by narrow submarginal hyaline strips, 0.3–0.8 μm in breadth. Wider marginal ridge, 0.8–2.0 μm in breadth, at mantle or along valve edge.

RV, external view (Figs 8 A – F , 11 A – D , 13 A, B , 15 A, C, D ). Central area small, round or rectangular. Raphe straight, proximal (central) endings drop-shaped, slightly extending into central area; distal endings more extending and frequently T-shaped. Areolae round or unevenly rounded, small along raphe, increasing towards valve edge.

RV, internal view (Figs 9 A – D , 11 E, F , 13 C , 15 B ). Central area round, axial and central areas slightly convex. Proximal raphe endings directed opposite; distal ones straight or directed opposite from each other and from proximal endings, i. e. raphe branches S-shaped. Hyaline area (submarginal hyaline strips) in form of ridge. Areolae round, equal in size, and occluded (not always) by hymen.

RVVC (Fig. 13 D ). Valvocopula connected conically to RV, closed or opened, up to 3 μm in breadth, with uneven edge bears and elongated weakly curved fimbriae, 0.9–1.8 μm high, 13–18 in 10 μm, some fimbriae with dichotomously branched tips.

SV (n = 45). Valves convex, increasing of convexity closer to valve edge. Central area and hyaline rings absent. Striae uniseriate, 17–28 in 10 μm (mean 25). Areolae round to unevenly rounded, sometimes elongated, 11–23 in 10 μm of stria (mean 18.7).

SV, external view (Figs 12 A – D , 14 A, B , 15 E ). Axial area narrowly linear or absent. Middle part of valve (not mantle) often with small granules arranged in order or randomly.

SV, internal view (Figs 10 A – D , 12 E, F , 14 C, D , 15 F ). Axial area narrowly linear to narrowly lanceolate, usually slightly raised as rib.

SVVC. Valvocopula closed, 1.3–1.7 μm in breadth.

There are no data on copulae, except valvocopulae.

Comments.

Our data differ from the data of Skvortzov and Skabichevsky in the following (Table 4 ): the valve length corresponds to Skvortzov’s description ( Skvortzov 1946). The upper range of valve width and the stria density on both valves are increased. The protologue data of 14 striae in 10 μm were not observed and are likely erroneous. Literature data on the areola density in striae most likely refer to a SV, according to our data it is somewhat higher than it is in the literature; while the areola density on the RV is significantly higher than on the SV.

Cocconeis baicalensis , in contrast to C. placentula Ehrenberg , has (1) broadly elliptical valves, (2) the lanceolate submarginal hyaline strip on the RV, (3) the stria density is higher on the RV and lower on the SV, (4) striae located along the valve edge are interrupted on / near the apices by the submarginal hyaline strips, (5) rounded areolae on the SV, (6) the sternum on the SV is clear on the internal surface.

We choose SEM photograph Fig. 9 C , as the epitype of C. baicalensis , to show the morphological features of the RV in the internal view, which are poorly represented in the type material, namely its 3 D-shape, density and arrangement of striae, shape and size of hyaline areas. Additionally, figures 8 A, 10 A and 12 C show the same traits of the RV in the external view and SV in the external and internal view.

The validating description of Cocconeis placentula var. baikalensis ( Williams and Reid 2001, 310) (≡ Cocconeis skvortzowii ) is “ based on a little bottom sample collected by Prof. K. I. Meyer at the depth of 33 meters near the Olhon Gate of Baikal Lake July 29, 1916 ” ( Williams and Reid 2001, 297). No specimen of this gathering has been found in LE. In its absence, the only element of the original material are the illustrations in the protologue ( Williams and Reid 2001, pl. 5, figs 5, 7, 8), two of which we are designating as the lectotype.

Since the drawings ( Williams and Reid 2001, pl. 5, figs 7, 8) do not demonstrate the morphological details, but only the valve outlines and a wide axial area on both valves, we are designating the epitype, namely SEM photograph Fig. 18 C of Skabichevsky’s material from the Island Bolchoy Ushkaniy. The epitype illustration clearly shows the morphological features of the RV and SV in the external and internal view, namely shape, density and arrangement of striae, shape and size of areolae.

Figures

Figure 3. Cocconeis baicalensis. LM. Lectotype. Slide No. 318 a, Kotelnikovskiy Mayak, LE A 0004242 A – K raphe valve L – AA sternum valve. Scale bar: 10 µm.

Figure 7. Cocconeis baicalensis. LM. Slide No. 5, Marituy, LE A 0002317 A, D sternum valve with valvocopula B, C, E, F raphe valve G valvocopula of raphe valve H sternum valve. Scale bar: 10 µm.

Figure 8. Cocconeis baicalensis. Raphe valve, external view. SEM. Specimen No. BL 15645, Island Bolshoy Ushkaniy. Scale bar: 5 µm.

Figure 9. Cocconeis baicalensis A – D raphe valve, internal view B valve with valvocopula. SEM. Specimen No. BL 15645, Island Bolshoy Ushkaniy. Scale bar: 5 µm.

Figure 10. Cocconeis baicalensis A – D sternum valve, internal view A, B valve with valvocopula D lowest valve (arrowhead). SEM. Specimen No. BL 15646, Island Bolshoy Ushkaniy. Scale bars: 5 µm.

Figure 11. Cocconeis baicalensis. Raphe valve (A – D) external view (E, F) internal view. SEM. Specimen No. 318, Kotelnikovskiy Mayak. Scale bars: 2 µm (A); 5 µm (B, D – F); 1 µm (C).

Figure 12. Cocconeis baicalensis. Sternum valve (A – D) external view (E, F) internal view. SEM. Specimen No. 318, Kotelnikovskiy Mayak. Scale bars: 5 µm (A, C, E); 2 µm (B, D, F).

Figure 13. Cocconeis baicalensis A – C raphe valve A, B external view C internal view D valvocopula (VCRV). SEM. Specimen No. 5, Marituy. Scale bars: 5 µm (A – C); 2 µm (D).

Figure 14. Cocconeis baicalensis A – D sternum valve A, B external view C internal view D valve with valvocopula. SEM. Specimen No. 5, Marituy. Scale bars: 5 µm (A, C, D); 2 µm (C).

Figure 15. Cocconeis baicalensis A, B raphe valve A external view B internal view C frustule D part of frustule, external RV and internal SV view E, F sternum valve E external view F internal view. SEM. Specimen No. 336, Boguchanskaya Gulf. Scale bars: 5 µm (A – C, E); 1 µm (D); 2 µm (F).

Figure 18. Cocconeis skvortzowii A – F sternum valve A, B external view B sternum with ghost raphe and ghost areolae C, D internal view. SEM. Specimen No. BL 15645, Island Bolshoy Ushkaniy. Scale bars: 4 µm (A, B, D); 5 µm (C).