Cymatosirella benguelensis Dąbek & Witkowski, 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 : 49-50

Cymatosirella benguelensis Dąbek & Witkowski sp. nov. ( Figs 23–33 [LM], Figs 34–43 [SEM])

Frustules rectangular in girdle view with undulate outline. Valves lanceolate, 4–12 µm long and 1–4 µm wide. Valve surface areolated with a ring of areolae present along the valve margin, 15–26 in 10 µm; some areolae irregularly scattered over valve face.

Type: — SOUTH AFRICA. Western Cape Province: Lamberts Bay , sand from the intertidal flat (32°5’179’’S; 18°18’701’’E), collected on 16 th February 2011, by Dąbek, Witkowski & Archibald ( SZCZ 17497 , holotype!) .

Habitat: —Lamberts Bay is located about 280 km north of Cape Town and is influenced by Atlantic Ocean water masses, part of the Benguela Current upwelling zone. Coastal water temperature rarely exceeds 19° C, salinity is ca. 35 ‰. Beaches are sandy, occasionally with rocky outcrops and tidal pools. Climate is moderate with hot and dry summers and wet, rainy and cold winters.

Etymology: —Named after the Benguela Current (Atlantic Ocean) which washes the west coast of South Africa.

Observations: —The frustules are rectangular in girdle view with an undulate outline ( Figs 23–28, 34– 36 ). There is a single, large plastid per cell ( Figs 32, 33 ). Cells solitary or forming small ribbon-like colonies with 2–4 cells ( Figs 27, 32, 33 ). The girdle is composed of 8–11 bands each with a single row of poroids ( Figs 34–36 ). The valves are lanceolate ( Figs 29–31, 36–40 ), 4–12 µm long and 1–4 µm wide. A marginal ring of areolae (15–26 in 10 µm) is present along the valve margin; other areolae are irregularly scattered across the valve face but less so in around the slightly raised centre of the valve ( Figs 37–40 ). The areolae are more densely packed near the apices. Externally, the areolae are closed by simple volate occlusions ( Figs 40, 42, 43 ). The ocelluli are composed of 12–14 porelli in the largest specimens and 6–8 in the smallest, with 3 central porelli ( Figs 36, 39, 41 ). Hyaline rings around ocelluli are present ( Figs 37, 41 ). Spines are probably hollow and tapered and are located in the central part of the valve and along the valve margin ( Figs 40, 42, 43 ). Processes, pili, pseudosepta nor fascia have not been observed.

Ecology and geography: — Cymatosirella benguelensis was most abundant in a sand sample from Lamberts Bay (SZCZ 17497) from an intertidal pool located close to rocky outcrops. A few valves were also observed in a sample from Elands Bay (SZCZ 17518). Cymatosirella benguelensis most probably belongs to the epipsammon.

Figures

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).