GENERA starting with "S"

Symmetrical biraphid - Although the valve margins of Scoliopleura are linear-lanceolate, the frustules are twisted about the apical axis. Longitudinal canals are present on both sides of the raphe. The raphe is slightly sigmoid because of the twist, or torsion, of the frustule. The proximal raphe ends are deflected in opposite directions and the distal raphe ends are divergent. Striae are formed by loculate punctae. A single species is found...

Symmetrical biraphid - The valve is linear, lanceolate, or elliptical with bluntly rounded poles. Polar bars, or transapical thickenings, are present in some taxa. The axial area is distinct, and may be expanded along the apical axis to form a conopeum. The external proximal raphe ends are dilated, while the distal raphe ends are deflected. Sellaphora is widespread in alkaline to brackish waters of neutral pH. It contains the former Navicula...

Nitzschioid - Simonsenia is a genus that possesses characters seen in both the Surirellaceae and the Nitzschiaceae. Its valve symmetry and general shape, with the raphe being present on only one valve margin, resembles that of many Nitzschia species. Also, the cribra of the areolae are similar to those in many Nitzschia species. However, its raphe is present in a canal that is raised above the valve surface, as in some species of...

Centric - Valves of Skeletonema are very lightly silicified and often collapse when dried, or dissolve with standard processing methods. The marginal fultoportulae are positioned at the base of each connecting or tubular process. This process links frustules into long colonies. A single rimoportula is located at the base of the connecting process. Skeletonema grows primarily in marine and estuaries. Species within the genus are...

Araphid - Frustules of Stauroforma are small, with an elliptic to lanceolate valve outline. The valves not centrally expanded. Rimoportulae are absent in species of Stauroforma. The striae are continuous across the valve face, although this feature may be difficult to resolve in the light microscope. Frustules are linked together into linear colonies. Spines may be present or absent. Stauroforma is composed of species formerly...

Symmetrical biraphid - Stauroneis has naviculoid and mostly solitary cells with two chloroplasts, one on each side of the cell against the cingulum. Valves range from almost linear to lanceolate to elliptic-lanceolate. The central area is a prominent transverse fascia, known as a “stauros”. The central fascia typically extends to the valve margins, where one to several short striae may be present. The striae are uniseriate and punctate....

Symmetrical biraphid - Valves of Staurophora are solitary and lanceolate, linear-lanceolate, or elliptic-lanceolate, often with protracted ends. Valve faces are strongly curved onto the mantle, which is relatively deep. As a result, cleaned frustules often come to rest in girdle view. A fascia is present and is interrupted at the margins by several short striae. These short striae may not be visible in valve view. Striae are composed of small...

Araphid - Staurosira valves are elliptical or cruciform in outline. In girdle view, the frustules are rectangular in shape. Cells often form colonies, joined by interlinking spines. The striae are narrow and composed of small, round areolae. Striae do not meet one another in the central sternum. Valves lack rimoportulae. Staurosira includes the former Fragilaria construens and its relatives. In the light microscope it can be...

Araphid - The valves of Staurosirella are elliptical, linear or cruciform. Striae are composed of lineolate areolae. Apical porefields are present at both ends of each valve. Rimoportulae are absent. Neighboring cells are linked together at valve faces to form colonies. Staurosirella includes the former Fragilaria lapponica, F. pinnata, F. leptostauron and their allies. Cells attach to substrates by short stalks secreted by the...

Surirelloid - The valves of Stenopterobia are narrow and may be straight or sigmoid in valve outline. Symmetry may be lanceolate or sigmoid. Like other members of the Surirellaceae, the raphe is positioned within a canal and positioned along the valve margin. The canal in Stenopterobia is raised above the valve, onto a keel. Species within Stenopterobia are typically are found in low conductivity, nutrient poor, acidic waters. For...

Centric - Stephanocyclus differs from Cyclotella by the absence of a two-layered valve wall. Stephanocyclus differs from Cyclostephanos by the absence of marginal chambers. Stephanocyclus contains species that were included with Cyclotella meneghiniana and its allies, including C. caspia, and C. quillensis. Many Stephanocyclus species, however, have not been formally transferred. Stephanocyclus species are widely distributed in...

Centric - The valve face of Stephanodiscus species is flat or concentrically undulate.The striae are radial and organized into bundles, or fasicles. Fasicles are separated from one another by costae. Spines are present on the valve margin and a marginal fultoportula may be positioned below the spines. Internally, the areolae are covered by domed cribra. Stephanodiscus is a diverse and widespread planktonic genus of freshwaters,...

Surirelloid - Cells of Surirella grow as single, isolated cells. The frustules may be either isopolar or heteropolar. Like other genera with in the family Surirellaceae, the raphe system is positioned along the margin of the valve. The raphe is located within a canal, which may be raised above the valve surface in some species. Cells may be highly silicified, with spines and silica nodules on the valve surface. Species in Surirella...

Araphid - Frustules are robust and typically needle-like. Cells typically form radiate colonies with cells attached by mucilage pads. Synedra ulna was recently separated, with many other freshwater taxa, and is now considered to reside in the genus Ulnaria (Compere 2001).