Cocconeis scutellum var. parva (Grunow) Cleve (1895: 170)

Riaux-Gobin, Catherine, Witkowski, Andrzej & Igersheim, Anton, 2018, Cocconeis scutellum var. parva (Bacillariophyceae) re-examination and typification, Phytotaxa 343 (1), pp. 20-34 : 23-24

Cocconeis scutellum var. parva (Grunow) Cleve (1895: 170)

Basionym:— Cocconeis scutellum f. parva Grunow in Van Heurck (1880 –1885: pl. 29, figs 8–9, reproduced here as Figs 4–5 ).

Description in Cleve (1895: 170):— ‘var. parva Grunow (1881) . L. 0.018 to 0.02; B. 0.01 to 0.017 mm. Upper V. with 11 rows of puncta in 0.01 mm. Marginal puncta elongated.Axial area narrow. V.H. Syn. pl. XXIX f. 8, 9. C. consociata and C. aggregata Kützing according to Grunow C. transversalis Gregory M. J. III p. 39 Pl. IV f. 7; 1854?’ [1857] ‘ C. scut . var. minor A.S. Atl. CXC. 22.’ (pl. 190, fig. 22). ‘Marine: Baltic! East Cape! Adriatic (Atl.).’

Lectotype (designated here):— Slide no 1035 in Grunow’s slide collection ( Fig. 8 , specimens illustrated in Figs 9–16 ) ( McNeill et al. 2012, art. 9.7). Nothing else has been traced that could be considered as original material studied by Albert Grunow. For both W and BR collections, no raw material (from which the slide was made) was found, thus SEM cannot be conducted on this material.

LM observation of the lectotype ( Figs 9–16 , Table 2):—The slide number 1035 ( Fig. 8 ), contains an abundance of small Cocconeidaceae , including numerous small individuals that match the drawings by Albert Grunow ( Figs 4–5 ). Valves oblong-elliptical with round apices ( Figs 9–16 ). Frustules 13–24 μm long, 8.0–14.5 μm wide, L/W 1.6 ± 0.1 (n = 32, Table 2). SV striae radiate, equidistant (11–14 in 10 μm) composed of round areolae arranged into apical rows ( Figs 13–16 ), with marginal groups of three to four coalescent areolae ( Figs 14–16 ). SV sternum narrow and straight. RV striae radiate, equidistant (12–14 in 10 μm), composed of round areolae ( Figs 9–12 ). Presence of a marginal well-marked RV rim ; valvocopula with irregularly positioned fimbriae ( Fig. 10 ). Raphe straight , proximal raphe endings well spaced ( Fig. 9 ) .

Remarks on the lectotype:—Grunow’s illustration in Van Heurck (1880 –1885: pl. 29, fig. 9 reproduced in Fig. 5 ), show similar stria densities for both valves (op. cit.: fig. 8, reproduced in Fig. 4 ). In the drawings by Grunow, the RV marginal scalar short bars (from the edge of the valve to the rim, Fig. 5 ) are not oblong areolae but instead, the fimbriae of the RVVC. From Fig. 4 (op. cit.), the marginal SV areolae are not unique transapically (or apically) oblong areola, but are built up with several coalescent small areolae. Figs 14–15 match the original drawings. Cocconeis scutellum var. parva SV , except for its small size and slightly denser striation than in the nominate variety, is very close to that of Cocconeis scutellum (e.g., Figs 2–3 ). See ‘ Cocconeis scutellum var. parva history and ambiguities’ in Discussion.

Epitype (here designated): population from Rodrigues Island, sample ROD1

LM observation of the epitype ( Figs 17–25 , Table 2):—Valves small, RV and SV stria density similar ( Table 2), SV with more or less regular axial rows of areolae ( Figs 17–19 ), SVVC (sternum valve valvocopula) closed, with short digit fimbriae ( Fig. 23 ). Numerous teratologic forms observed ( Figs 24–25 ).

SEM observation of the epitype ( Figs 26–32 , Table 2):—Valves small ( Table 2), oblong elliptical, with round to sub-quadrangular SV areolae, SV striae uniseriate with marginal cluster of small areolae ( Fig. 26 ). SV and RV areola hymenes flat, with radially arranged marginal slits and scattered dots in mid-part ( Fig. 30 ). RV with continuous submarginal hyaline area in external view ( Fig. 29 arrowhead) and internal continuous rim with bumps ( Fig. 28 arrow). RVVC fimbriae on each virga, absent on rim, and bumps ( Fig. 32 ). Regularly spaced fimbriae, oblong papillae with several transverse furrows on abvalvar side ( Fig. 32 arrowhead). SV and RV areola hymenes ( Figs 30–31 ) with short radial slits.

Remarks on the epitype:—The morphometrics and morphology of the specimens from some other tropical prospected sites ( Table 2, not illustrated) were very similar to those in Rodrigues (except for the RVVC papillae that are often longer). These tropical specimens were assigned to C. scutellum cf. var. parva . It cannot be dismissed that these tropical taxa may all pertain to a continuum from the nominate variety for the larger ones, to C. scutellum var. parva for the smaller ones.

Figures

FIGURES 1–7. Published drawings of: Cocconeis scutellum Ehrenberg (1838: 194, pl. 14: fig. 8/1–4, reproduced in Fig. 1; Van Heurck 1880–1885, pl. 29, figs 1–2, reproduced in Figs 2–3); Cocconeis scutellum f. parva Grunow in Van Heurck 1880–1885 (pl. 29, figs 8–9, reproduced in Figs 4–5: Reproduction of original sketches drawn by Grunow (Grunow’s ‘Bilder-Sammlung’, Acqu. 1901/3604); C. scutellum var. parva Grunow (illustrated in Peragallo & Peragallo 1897–1908, pl. 4, figs 3, reproduced in Figs 6–7). Scale bars = 20 μm.

FIGURES 8–16. Albert Grunow collection, slide no. 1035 housed in W (8); Cocconeis scutellum f. parva RV (9–12), note the marginal rim and the RVVC fimbriae (10, 12); C. scutellum f. parva SV (13–16). Scale bars = 10 μm.

FIGURES 17–25. Cocconeis scutellum var. parva epitype (Rodrigues Island). LM. Figs 17–25. SV views (17–19), RV views (20–22), SVVC (sternum valve valvocopula) (23), teratologic forms (24–25). Scale bar = 10 μm.

FIGURES 26–32. Cocconeis scutellum var. parva epitype (Rodrigues Island). SEM. Figs 26–32. SV external view (26), with the advalvar side of the SVVC (Sternum valve valvocopula) fimbriae with undulating basis (26 arrow); RV internal view with the RVVC (Raphe valve valvocopula) still in place (28); SV internal view (27), with the SVVC digit fimbriae in abvalvar view; RV external view (29), with the marginal rim (29 arrowhead); SV areola hymenes with radial slits arranged by sectors and median part with dots (30 external view); RV areola hymenes with marginal radial slits (31 external view); RVVC in abvalvar view, with oblong papillae with transverse furrows (32) and a bump (32 arrowhead). Scale bars = 4 μm (Figs 26, 28–29), 700 nm (Fig. 27), 400 nm (Fig. 32), 300 nm (Fig. 30), 200 nm (Fig. 31).