Staurosirella antarctica Van de Vijver & E. Morales 2014, sp. nov.

Staurosirella antarctica Van de Vijver & E.Morales sp. nov. (Figs 26–51)

Cells lanceolate to ovoid, heteropolar, with openly convex margins and subrostrate to rounded apices. Length 9.5–15.5 µm, width 2.9–3.9 µm, stria density 9–10 in 10 µm. Central sternum narrow, linear to lanceolate, raised and forming a continuum with the virgae. Striae alternate, parallel in central area and radiate at apices. Areolae markedly lineolate, running continuously from valve face to mantle, 55–60 in 10 µm, and bearing well-developed volae. Spines flat, spatulate and located on the virgae. One apical pore field at each apex, located on the valve mantle. Foot-pole apical pore field larger and compose of up to 5 rows of round poroids. Girdle bands open, non-perforated with valvocopula wider than rest of girdle elements.

LM (Figs 26–45): Frustules are rectangular in girdle view (Fig. 45). Valves are lanceolate to narrowly ovoid, faintly or conspicuously heteropolar with subrostrate to rounded apices (Figs 26–44). Valve dimensions (n=25): length 9.5–15.5 µm, width 2.9–3.9 µm. The central sternum is narrow and linear to lanceolate. The striae are alternating, parallel and becoming slightly radiate near the apices, 9–10 in 10 µm. The areolae are not discernible in LM.

SEM (Figs 46–51): Frustules are linked by single, spatulate and solid linking spines, which are located on the costae at the valve face/mantle junction (Figs 46–49). The valve surface is slightly undulate due to the raised costae and the axial area, which are smooth (Fig. 47). Apical pore fields are present on each apex, better developed at the foot-pole that at the head-pole. They are located on the valve mantle and composed of several, usually up to 6, rows of small round poroids (Figs 47, 49, 51). Internally, the apical pore fields are well separated from the striae and formed within a depression at the valve apices (Fig. 50). Rimoportulae are absent. The striae are composed of narrow slit-like to rectangular areolae running continuously from the valve face onto the mantle and becoming smaller toward the axial and mantle abvalvar areas (Figs 48, 49). Areolae ca. 55–60 in 10 µm along the striae (Figs 47–49). The mantle areolae, usually 4-5, are gradually becoming smaller than the areolae toward the axial area (Fig. 48). The volae are clearly developed and form a complex structure within the areolae (Fig. 47–49). Internally, the costae are also raised and thickened compared to the striae (Fig. 50). The girdle bands are open and lack perforations (Fig. 46). The valvocopula are presumably fimbriate and wider than the other narrower copulae (Fig. 46).

Type:— ANTARTICA. Pool near Limnopolar Lake, Byers Peninsula, Livingston Island (South Shetland Islands), sample BY049 (62°38’43.1”S, 61°06’22.9”W), Leg. B. Van de Vijver, coll. date 14/01/2009 (BR-4326 holotype!, University of Antwerp, Belgium slide PLP-227, isotypes).

Etymology:—The species epithet refers to the general geographic area were this diatom was found.

Ecology & Distribution:—Due to force-fitting, all Staurosirella populations in the Maritime Antarctic Region have been grouped under Staurosirella (Fragilaria) pinnata making it at present impossible to determine the exact distribution of the new species. Staurosirella antarctica was with certainty found in one small pool (10 m diameter) close to Limnopolar Lake. On one side of the pool water was dripping from a rock surface in the pool while on the other side, water was flowing out in a small braided river. The bottom was covered sediment with fine sediment and larger pebbles. Thin algal mats were present in the pool. The pool had a rather alkaline pH (7.6) with a low specific conductance value (58 µS/cm).