Cocconeis pinnata W. Gregory ex Greville 1859

Riaux-Gobin, Catherine, Compère, Pierre, Romero, Oscar E. & Williams, David M., 2014, Cocconeis pinnata W. Gregory ex Greville (Bacillariophyta): Lectotypification and an emended description after examination of type material and South Pacific specimens, Phytotaxa 156 (3), pp. 81-99 : 85-86

Cocconeis pinnata W. Gregory ex Greville 1859

Cocconeis pinnata W. Gregory ex Greville (1859: 79 ; pl. 6, fig. 1) emend Riaux-Gobin, Compère, Romero & Williams ( Figs 7–43 )

non Cocconeis pinnata (Hustedt) Cleve-Euler (1934: 43 , illegitimate homonym [basionym: Achnanthes pinnata Hustedt 1922: 123 , pl. 9, figs 15–18] = Planothidium conspicuum (Mayer) Aboal in Aboal et al. (2003: 163) [basionym: Achnanthes conspicua Mayer 1919: 198 , pl. 6, figs 9, 10].

Synonyms: Disconeis pinnata (W. Gregory ex Greville) Cleve 1895: 181 Pleuroneis pinnata (W. Gregory ex Greville) E. G. Jørgensen 1905: 208

Valves elliptical to ovoid, slightly tapering toward apices ( Figs 13 , 21 ). Dimensions of type specimens: Valve dimensions 26.9–36.9 µm length, 16.5–27.2 µm width. SV: 5.0 + 0.3 striae in 10 µm. RV: 21.9 + 1.1 striae in 10 µm, observed specimens n = 21 ( Table 1). Dimensions of specimens from Tahiti: 22.2–36.5 µm length, 14.1–22.4 µm width. SV: 6.3 + 0.6 striae in 10 µm. RV: 26.5 + 1.7 striae in 10 µm (SEM specimens n = 14; LM specimens n = 13, Table 1).

Sternum valve with relatively wide elliptical axial area ( Fig. 19 ), marginal area lacking areolae and externally depressed along inter costae ( Figs 19, 21, 24 ). Striae robust, raised, and radiate, biseriate near margin, 6.3 + 0.6 striae in 10 µm. Areolae in centre part of valve slightly trans-axially elongated ( Figs 19, 24 , 27 ), while elsewhere ± rounded ( Fig. 26 ). Areolae externally ornamented by complex arborescent volae ( Figs 26–29 ), internally occluded by hymen with radial slits ( Fig. 31 ). Small ‘pearls’ or spherical corpuscles spread over entire valve ( Figs 19, 20, 21 ), sometimes randomly, but often aggregated i.e., along sternum. SV valvocopula visible in LM ( Figs 14, 18 ), wide, flat and thick, open at one apex ( Fig. 30 , arrows; Fig. 32 ), bordered by large and ± regular fimbriae, overlapping each intercosta ( Fig. 30 ; Figs 34–35 , arrows). In internal view, wide fimbriate of SV valvocopula cover marginal ends of striae, creating loculi with rounded ends ( Fig. 32 , arrow; Figs 34, 35 ).

Raphe valve flat to slightly concave. Raphe straight, filiform, with simple distal raphe endings very close to margin ( Fig. 37 ). Central raphe endings close to each other and coaxial ( Fig. 38 ). Axial area narrow and straight. Central area very small and oblong ( Fig. 38 ). Striae dense and radiate (26.5 + 1.7 in 10 µm), composed of small, round areolae with one marginal row of ‘flame’-like areolae ( Figs 42–43 ). Shorter intercalary striae present ( Fig. 42 , arrows). Areolae slightly transversely elongated at valve centre ( Fig. 37 ), internally closed by hymenate occlusions ( Fig. 43 ), externally ornamented by 2 (4 near margin) short-branched volae ( Figs 37, 39 ). Helictoglossae non-protruding, straight ( Fig. 43 ). RV valvocopula opened at one apex ( Fig. 36 , arrow). In addition to valvocopulae, cingulum consisting of at least one flat copula ( Fig. 40 , arrow).

Type:— SCOTLAND, UK. Arran ( Arran Island ), Firth of Clyde , ' Lamlash Bay, in the island of Arran. Dredged by Professor Balfour 1857', Greville (1859: 79) (lectotypus hic designatus, BM 4986 , specimen located at sector 5, position 4 S, 14.5 E, see Figs 9, 10 ; BM 1465 , BM 1467 , BM 1468 , BM 4985 , BM 4997 , BM 4998 , syntypes) .

Greville (1859) provided a description of only the SV, illustrated with a single line drawing (pl. 6, fig. 1 reproduced here as Fig. 4 ). He did not refer to any particular specimen and although a great many of Greville’s original pencil drawings are extant in BM (these drawings are usually annotated with slides numbers, specimens locations, etc.), this particular drawing is not among them.

Of the numerous slides in BM labelled ‘Arran 57’, 7 may be considered syntypes since they have one or more specimens of Cocconeis pinnata labelled and circled on the coverslip by Greville. These are as follows: BM 1465 , one specimen (labelled as circle number 2); BM 1467 , four specimens (labelled as circle numbers 2, 4, 7, 8); BM 1468 , three specimens (labelled as circle numbers 1, 2, 5); BM 4985 , two specimens (labelled as circle numbers 2, 3); BM 4986 , one specimen (labelled as circle number 5); BM 4997 , four specimens (labelled as circle numbers 2, 5, 7, 8); and BM 4998 , two specimens (labelled as circle numbers 2, 7), yielding a total of 17 specimens. All the slides are in relatively good condition, to a certain degree darkened, with some having several specimens of C. pinnata not circled or named by Greville (see Figs 7, 8 , from slide BM 4986 , close to sector 6). Among these specimens, several complete frustules and detached SV were found, no detached RV was encountered. Micrographs ( Figs 7–12 ) of complete frustules shown at two different foci have been taken from slides BM 4986 and BM 1467 .

Observations: — Type specimens: The SV axial area is largely elliptical and its striae strongly moniliform, uniseriate near the sternum, bi- to tri-seriate near the margin. As observed in the LM, the SV structure of type material specimens conforms to the original description. With a modern LM it is relatively easy to resolve the fine striation on the RV (22.2 + 2.3 striae in 10 µm, Table 1, Figs 8, 10, 12 ). The RV striae are radiate and regularly spaced throughout. The raphe is straight and the central raphe endings are clearly close to each other ( Fig. 8 ) .

Tahiti Specimens: The specimens found on Tahiti Island are very similar to the type specimens, although there are some differences such as the slightly smaller valve dimensions and a SV axial area slightly smaller than in the type ( Table 1) that may be due to morphological plasticity.

The specimen of Cocconeis pinnata illustrated by Witkowski et al. (2000, pl. 37, fig. 14; no RV illustrated) also has a narrower axial area than in the type. Contrary to the assumption of Grunow and several later authors, it can be noted that the RV of C. pinnata , even if densely striated, is very different to that of C. pseudomarginata (illustrated as Cocconeis major W. Gregory 1857b : fig. 28; Hustedt 1933: fig. 813b; De Stefano & Romero 2005: pls 30, 31). Furthermore, there is no evident affiliation of C. pinnata with C. costata W. Gregory ( Gregory 1855, 1857a), as stated by Jørgensen (1905: 208), since the RV of C. pinnata does not have a marginal rim, externally or internally. The central raphe endings are very close to each other ( Figs 8 , 38 ) and not 'somewhat separated' or 'clavate', as stated by Jørgensen (1905: 208), who does, however, note the presence of loculi, also observed in our specimens ( Figs 32, 34, 35 ).

Figures

FIGURES 7–12. Cocconeis pinnata from type slides (LM). On the cover slip of each slide, numbered diamond circled sectors localise specimens labelled on the slide margin. A rough benchmark gives now origin on each slide. Fig. 7, SV; Fig. 8, RV: from slide BM 4986, a specimen not circled by Greville, close to sector 6, coordinates 9 S, 19.5 E. Fig. 9, SV; Fig. 10, RV: Lectotype from slide BM 4986, circled specimen, sector 5, coordinates 4 S, 14.5 E. Fig. 11, SV; Fig. 12, RV: from slide BM 1467, circled specimen, sector 3, coordinates 2 S, 12.5 E. LM, scale bars: Figs 7–12: 10 µm.

FIGURES 13–18. Cocconeis pinnata from Tahiti Island (LM). Fig. 13, RV striae (arrow). Fig. 14, RV showing the central raphe endings, and SV valvocopula (arrow). Fig. 15, RV, Fig. 16, SV, Fig. 17, RV with central raphe endings (arrow). Fig. 18, SV showing the digitate SV valvocopula. LM, scale bars: Figs 13–18: 10 µm.

FIGURES 19–25: Cocconeis pinnata from Tahiti Island (SEM). External views of the SV. Fig. 19, 20, 21: complete valve. Fig. 22: detail of the margin, with pearls-globular corpuscles spread on the striae. Figs 23, 24: apex and detail of the apically/axially elongated areolae in mid-valve. Fig. 25: open SV valvocopula (arrows). SEM, scale bars: Fig. 20: 8 µm; Fig. 21: 6 µm; Fig. 19: 5 µm; Fig. 24: 3 µm; Figs 22, 23, 25: 1 µm.

FIGURES 26–29: Cocconeis pinnata from Tahiti Island (SEM). External views of the SV. Figs 26, 28, 29: details of the areolae from the margin of the valve, with complex arborescent volae and pearls-globular corpuscles in between. Fig. 27: detail of the axially elongated areolae in the mid-valve. SEM, scale bars: Fig. 27: 1 µm; Fig. 26: 0.7 µm; Figs 28, 29: 0.5 µm.

FIGURES 30–35: Cocconeis pinnata from Tahiti Island (SEM). Internal views of the SV. Fig. 30: complete valve, with the SV valvocopula open at one apex (arrows). Fig. 31: detail of the areolae hymen with radial long slits. Fig. 32: SV valvocopula expending on the margin, with digitate long fimbriae taking place on the interstriae. The valvocopula manages a space between the valve and the copula (visible on the broken apex) and creates loculi (arrow). Figs 33, 34, 35, detail of the loculi and digitate fimbriae endings (arrows). SEM, scale bars: Fig. 32: 6 µm; Fig. 30: 5 µm; Fig. 34: 2 µm; Figs 33, 35: 1 µm; Fig. 31: 0.7 µm.

FIGURES 36–40: Cocconeis pinnata from Tahiti Island (SEM). External views of the RV. Fig. 36: complete valve, with the RV valvocopula open at one apex (arrows). Fig. 37: detail of the areolae on apex, and distal raphe ending close to the margin. Fig. 38: central area restricted and central raphe endings opposed and close to each other. Fig. 39: detail of the arborescent volae closing the areolae (most often two per areolae). Fig. 40: relatively narrow cingulum with a supplementary cingular band/copula (arrow). SEM, scale bars: Fig. 36: 7 µm; Fig. 40: 3 µm; Fig. 38: 2 µm; Fig. 37: 1 µm; Fig. 39: 0.3 µm.

FIGURES 41–43: Cocconeis pinnata from Tahiti Island (SEM). Internal views of the RV. Fig. 41: complete valve, without the RV valvocopula. Note the fine radiate striation and absence of marginal rim. The helictoglossae are very close to the margin. Fig. 42: detail of the marginal oblong flame-like areolae and rounded areolae structured on a hexagonal pattern. Note the presence of short intercalary marginal striae (arrows). Fig. 43: detail of the simple and straight low raised helictogloss. Note the internal hymenate pore occlusion of the areolae. SEM, scale bars: Fig. 41: 5 µm; Fig. 42: 1 µm; Fig. 43: 0.4 µm.

FIGURES 2–6: Fig. 2: Cocconeis pinnata var. artica Østrup (1910, pl. 13, fig. 13); Fig. 3a,b: C. pinnata illustrated by Grunow in Van Heurck (1880–1885, figs 6, 7); Fig. 4: C. pinnata Gregory ex Greville (Greville 1859, fig. 1); Fig. 5a,b,c,d,e: C. pinnata illustrated by Peragallo & Peragallo (1897–1908, pl. II, figs 11–14); Fig. 6a,b,c,d,e,f: C. pinnata illustrated by Schmidt (1877–1958, pl. 189, figs 1–5). LM, scale bars: 10 µm.