Cymatosirella Dąbek, Witkowski & Sabbe, 2013

Dąbek, Przemysław, Sabbe, Koen, Witkowski, Andrzej, Archibald, Colin, Kurzydłowski, Krzyszof J. & Zgłobicka, Izabela, 2013, Cymatosirella Dąbek, Witkowski & Sabbe gen. nov., a new marine benthic diatom genus (Bacillariophyta) belonging to the family Cymatosiraceae, Phytotaxa 121 (1), pp. 42-56 : 46-49

Cymatosirella Dąbek, Witkowski & Sabbe gen. nov. ( Figs 2–58 )

Typus generis: Cymatosirella capensis (Giffen) Dąbek, Witkowski & Archibald comb. nov.

Cells rectangular and undulate in girdle view, single or a few cells joined together in short ribbon-like colonies, one plastid per cell. Frustules isovalvate without processes. Cingulum composed of numerous bands, each with one row of poroids. Valves elliptical to lanceolate, with rounded apices. Valve face undulate and areolate. Both apices bearing ocelluli, surrounded by an unperforated rim; porelli sometimes with spines in-between. Valve mantle deep without perforations. Areolae closed by cribra, volae or apparently without occlusions. Spines few, scattered on the valve face. Processes, marginal spines, marginal ridges, pili, pseudosepta or fascia are absent.

Etymology: —The generic name refers to the resemblance of this new genus to Cymatosira and to its very small size.

Cymatosirella capensis (Giffen) Dąbek, Witkowski & Archibald comb. nov. ( Figs 2–13 [LM], Figs 14–22 [SEM]) Basionym: Cymatosira capensis Giffen (1975: 79 , figs 36–39).

Type: — SOUTH AFRICA. Western Cape Province: Langebaan Lagoon, Saldanha Bay (Giffen slide G 630 /7, holotype!). Frustules rectangular and distinctly undulate in girdle view, valve mantle deep and unperforated. Valves elliptical to lanceolate with cuneate to rounded apices, 4,5–11 µm long, 2–3 µm wide. Valve surface areolate, areolae arranged either in a quincunx pattern or irregular, ca. 15–18 in 10 µm .

Habitat: —Atlantic Ocean, Langebaan Lagoon, rocky tidal flat overgrown by macroalgae mats. Langebaan Lagoon is a part of Saldanha Bay, located around 100 km north of Cape Town. This area is strongly influenced by water masses of the Atlantic Ocean and the cold, nutrient-rich Benguela Current. Langebaan Lagoon is sheltered from the coast, therefore sea surface temperature and salinity is much higher. The difference in the water temperature could be even more than 10ºC between the open coast and Langebaan Lagoon, while the salinity is slightly higher than 35 ‰.

Observations: —The frustules are rectangular and distinctly undulate in girdle view, ( Figs 2–11, 14 ). Cells are solitary or 2–4 cells joined together in short ribbon-like colonies ( Fig. 10 ). The girdle is composed of numerous bands, each with one row of poroids ( Figs 14, 15, 18 ). The valves are elliptical (smaller specimens) to lanceolate (larger specimens) with cuneate to slightly rounded apices, 4,5–11 µm long, 2–3 µm wide ( Figs 12, 13, 16, 17 ). The valve surface is perforated by areolae externally closed by cribra; the areolae are more or less arranged in a quincunx pattern (cf. Giffen 1975) or irregularly, ca. 15–18 in 10 µm ( Figs 16, 17 ); the areolae are easily visible in LM. Each valve bears two slightly elevated ocelluli ( Figs 14–17 ), which are surrounded by an unperforated rim. The ocelluli are composed of 12–15 porelli with small spines set inbetween ( Figs 20, 21 ); there are four central porelli ( Figs 17, 20 ). The valve mantle is deep and unperforated ( Figs 18, 19 ). Spines are irregularly placed on the valve face but mainly occur around the centre of the valve ( Figs 15–17 ); they are hollow and tapered ( Fig. 22 ). Processes, pili nor fascia have not been observed.

Ecology and geography: — Cymatosirella capensis was found only in tidal and intertidal samples from the west coast of South Africa. It was most abundant in samples with sand (SZCZ 6849 = G628, SZCZ 6850 = G629, SZCZ 17537) and with seaweeds e.g. species of Enteromorpha and Ectocarpus (SZCZ 6851 = G630/ 7, SZCZ 6853 = G633) in the Langebaan Lagoon ( Giffen 1975). A few specimens were also identified in a sandy sediment sample from Blaauwberg beach near Cape Town (SZCZ 17589). Cymatosirella capensis is most probably an epipsammic and/or epiphytic intertidal diatom species.

Figures

FIGURES 2–22: Cymatosirella capensis (Giffen) Dąbek, Witkowski & Archibald comb. nov., Langebaan Lagoon, South Africa. Following images originate from: slide G630/2 (figs 10–15, 17), G628 (figs 3,4), G629 (figs 5–9), SZCZ 17582 (figs 18–21), SZCZ 17589 (figs 16, 22). Fig. 2: Original drawings of Malcolm H. Giffen of Cymatosira capensis (Giffen 1975). Figs 3–13: LM images. Scale bar = 10 µm. Figs 14–22: SEM images. Figs 14, 15: Frustule in girdle view with distinctly undulated outline and spines (arrowhead). Figs 16, 17: Valve view, each elevation bearing an ocellulus (arrowhead) surrounded by unperforated rim. Note the areolae with external cribra. Fig. 18: External view of the mantle and cingulum. Girdle bands are perforated by the one row of poroids (arrowhead). Fig. 19: Internal view of the mantle and areolae. Figs 20, 21: External view of ocelluli composed of porelli with small spines (arrowhead). Fig. 22: Valve surface view with hollow spines and areolae with external cribra.

FIGURES 23–43: Cymatosirella benguelensis Dąbek & Witkowski sp. nov., Lamberts Bay, South Africa. All images originate from the holotype slide SZCZ 17497. Figs 23–33: LM images. Scale bar = 10 µm. Figs 32, 33: Living cells with plastids. Figs 34–39, 41, 42: SEM images. Figs 40, 43: TEM images. Figs 34–36: Frustule in girdle view with complete cingulum. Bands with one row of poroids (arrowhead). Fig. 37: External view of valve. Note the simple occlusions closing areolae and spines on the valve face. Figs 38, 39: Internal view of the valve and ocelluli. Fig. 40: Valve with occlusions (arrowhead) and spines (arrow). Fig. 41: Ocellulus composed of 13 porelli (3 central porelli). Figs. 42, 43: Central, bulged part of the valve face surrounded by one row of poroids and spines. Fig. 43: Detail of valve showing occlusions (arrowhead) and spines (arrow).

FIGURES 44–58: Cymatosirella taylorii Dąbek & Witkowski sp. nov., Langebaan Lagoon, South Africa. All images originate from the holotype slide SZCZ 17582. Figs 44–51: LM images. Scale bar = 10 µm. Figs 52–58: SEM images. Fig. 52: Frustules in girdle view with complete cingulum, girdle band perforated by one row of poroids (arrowhead). Figs 53–55: Valve face view. Note the poroids on the valve surface without occlusions and ocelluli surrounded by the rim. Fig. 55: Valve with spines (arrowhead). Fig. 56: Internal view of the valve. Fig. 57: Ocellulus in external view, composed of 8 porelli (1 central), surrounded by an unperforated rim. Fig. 58: Ocellulus in internal view, composed of 10 porelli (2 central).