Cocconeis diaphana W.Sm. ( Smith 1853 )

Riaux-Gobin, Catherine, Compère, Pierre, Jordan, Richard W., Coste, Michel & Yesilyurt, Jovita C., 2016, Cocconeis molesta Kütz., C. diaphana W. Sm. and C. dirupta W. Greg. (Bacillariophyta): type material, ambiguities and possible synonymies, European Journal of Taxonomy 204, pp. 1-18 : 8-11

Cocconeis diaphana W.Sm. ( Smith 1853)

Figs 2–3 , 21–34 , Table 1

Cocconeis molesta var. amygdalina Grunow ex Cleve (1895: 174) .

Cocconeis amygdalina Bréb. ex Grunow in Van Heurck (1880 –1885: pl. 30, figs 22–23), nom. inval.

Original description

Smith (1853): 22, pl. 30, fig. 254, reproduced in Figs 2–3 .

“ Cocconeis diaphana , n. sp. V. elliptical, scarcely siliceous, diaphanous; striae obscure. Length.0012” to.0018” (30.48 to 45.72 µm). v.v. β Nodule dilated into a Stauros. Marine. Sidmouth, Miss Cutler, communicated by Dr. Greville. Pontac, Jersey, Aug. 8, 1852, W. Sm. Supp. Plate XXX. 254”.

Type material

“Marine. Sidmouth, Miss Cutler…” “Pontac, Jersey… W. Sm.”, syntypes; “Pontac, Jersey… W. Sm.”, BM 23161 , here designated as lectotype; BM 23162 , isolectotype ; The other syntype, BM 19589, from Sidmouth, belongs to C. dirupta Gregory.

Notes

When W. Smith introduced C. diaphana , he also proposed an unnamed variety β characterized by “the nodule dilated into a stauros”. This variety, mostly represented in the Sidmouth gathering, though originally a syntype must be excluded from this species. It will be here treated as belonging to C. dirupta W.Greg. (see further comments under this species). The original drawings of C. diaphana ( Smith 1853, fig. 254) show relatively oblong valves, one without any stauros, the other, marked β, with a distinct stauros on the RV.

Van Heurck (1896: pl. 29, fig. 823bis) reports Cocconeis molesta var. amygdalina as a “synonym of C. diaphana W.Sm. partim, S. B.D., i., p. 22, pl. 30, fig. 254; H. V. H. Atl., pl. 30, figs 5 and 35”, and comments that it is: “much larger in size, 3.5 to 4.5 c.d.m. (35 to 45 µm). Central nodule rounded, surrounded by small hyaline area. Marine [...] Jersey ( W.Sm.)”.

Description of specimens from “ Jersey, Pontac”, after LM examination of the type material

BM 23161 ( Figs 21–26 ) contains oblong-elliptical, thinly silicified and diaphanous valves, 33–42 µm (38 µm ± 2.5 σ) long, 21–26 (23 µm ± 2.2) wide, l/L 1.65 ± 0.2, with 26 ± 2.2 SV striae in 10 µm, 25 ± 0.7 RV striae in 10 µm, and ca. 23 axial SV rows in a zig-zag pattern ( Fig. 26 ). The SV sternum is straight and narrow, the central area very reduced ( Figs 23–24 ). The RV has clearly identifiable striae, with 25 areolae in 10 µm. The RV fascia is short and quite high, with the aspect of an elliptic central area more than a real fascia. The helictoglossae are straight and off the margin ( Fig. 24 ). As this slide (BM 23161) contains the specimen best matching the original description, we here designate it as the lectotype of C. diaphana W.Sm.

Remark

Thanks to the kindness of Bart Van de Vijver we have received several SEM photographs of the isolectotype of Cocconeis diaphana deposited in the Van Heurck collection in Meise (BR). This material is epiphytic on marine Rhodophyceae, and is present on a mica labelled “ Cocconeis diaphana n.sp., Jersey, Aug. 14. 1852 ”, preserved in the W. Smith collection, vol. I, p. 33. These SEM photographs ( Figs 39–44 ) are a perfect match for the LM figures in this paper and support our emended description.

Description of specimens from “Sidmouth”, after LM examination of the type material

The Van Heurck collection (VI-45-B10, Figs 27–32 ) has specimens that are 15–24 µm (20.5 ± 3.2 σ) long, 14–18.3 (16 ± 2.4) wide, l/L 1.28 ± 0.1, with 18.7 ± 1.1 SV striae in 10 µm, and 22.7 ± 2.2 RV striae in 10 µm. Slide VI-45-B10 only shows the var. β.

The W. Smith collection (BM 19589, Figs 33–34 ) has specimens that are 19–26 µm (22 ± 2.9 σ) long, 16-20 (18.6 ± 2) wide, l/L 1.19 ± 0.05, with 20 ± 1.4 SV striae in 10 µm, and 22 ± 0.5 RV striae in 10 µm.

Valves round-elliptical, relatively small. The SV is coarsely striated and punctuated, usually with no axial rows of areolae. The SV sternum is large and composed of two lanceolate parts ( Figs 27–29, 33 ), one median SV stria lacking on one side ( Fig. 27 , arrow) or both ( Fig. 33 ). The RV has coarsely punctuated striae, strongly radiate. The RV fascia is narrow and wide (often more than half a valve in length). The raphe is often slightly sigmoid with helictoglossae deflected towards opposite sides ( Fig. 34 ). Slide BM 19589 only shows the variety β.

The two examined slides of “ C. diaphana Sidmouth ” (VI-45-B10/BR and BM 19589) show valves with similar characteristics ( Figs 27–34, 33–34 ), close to those of Cocconeis dirupta W. Gregory ( Figs 35–38 , see below). Therefore, var. β is here excluded from C. diaphana and considered as a synonym of C. dirupta .

Figures

Figs 1–8. Original drawings. 1. Cocconeis molesta Kütz. (Kützing 1844, pl. 5, fig. 7). 2–3. Cocconeis diaphana W.Sm. (Smith 1853, pl. 30): 2. var. β. 3. type C. diaphana var. diaphana. 4. Cocconeis dirupta W.Greg. (Gregory 1857, pl. 9). 5–8. Cocconeis molesta var. crucifera Grunow ex Cleve (Van Heurck 1880–1885, pl. 30): 5–6. f. minor. 7–8. f. major.

Figs 21–26. Cocconeis diaphana W.Sm. var. diaphana from BM 23161, “Jersey, Pontac”. 23. Lectotype illustration. SV sternum narrow and straight (21–22), SV central area small (21, arrow), SV axial rows in a zig-zag pattern (21–22, 26). RV striation easily discernible and beaded (23, arrowhead), RV central area transapically enlarged but short (24, arrows), proximal raphe endings robust and close (25). Scale bars = 10 µm (21–25), 5 µm (26).

Figs 27–34. Cocconeis diaphana W.Sm. “Sidmouth” (var. β). 27–32. From VI-45-B10 (H.F. Van Heurck collection). One SV stria lacking on one side, or both sides (27, arrow, 28–29), RV fascia narrow and extended (30, arrowheads), raphe slightly sigmoid (31, arrowhead), proximal raphe endings robust (30–32). 33–34. From BM 19589, SV sternum in two lanceolate parts (33, arrowhead), helictoglossae deflected in opposite directions (34, arrowheads). Scale bars = 10 µm.

Figs 39–44. Cocconeis diaphana W.Sm. isolectotype SEM illustration. Mica labelled as “Cocconeis diaphana n.sp., Jersey, Aug. 14. 1852”, deposited in the Van Heurck collection in Meise (BR). SV external view with a reduced central area (39, arrow) and striae composed of transversally elongated alveoli (39). SV internal view (40). Note the SV valvocopula (SVVC) with a smooth edge (40, arrowhead). Detail of the SV apex (41). Detail of a broken SV showing the double layered structure of the alveoli (42). RV external view with the central oblong-elongate central area reaching less than ¼ of the valve width (43, arrow). RV internal view with a low and straight helictoglossa (44, arrow) and the RV valvocopula (RVVC) with a smooth edge (44, arrowhead). Scale bars = 10 µm (39, 40, 43–44), 2 µm (41), 1 µm (42).

Figs 35–38. Cocconeis dirupta W.Greg. from BM 1420. 37. Lectotype illustration. SV sternum lanceolate with apices slightly bent in opposite directions (36), one SV stria lacking on one side (35, 36, arrow), RV striae strongly radiate, RV fascia narrow and extended (38, arrows), helictoglossae deflected in opposite directions (37, arrowheads) and raphe slightly sigmoid (37). Scale bars = 10 µm.