GENERA starting with "s"

 

Scoliopleura

  1. Valves twisted about apical axis
  2. Longitudinal canals evident on both sides of the raphe
  3. Proximal raphe ends deflected in opposite directions

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...


Sellaphora 11

  1. Valve linear, lanceolate or elliptical
  2. Polar bars at apices in some taxa
  3. Striae uniseriate
  4. Conopeum present in some taxa

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...


Simonsenia 1

  1. Raphe within a raised canal
  2. Raphe positioned on valve margin
  3. Valve with regularly spaced depressions near margin

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...


Skeletonema

  1. Valves lightly silicified
  2. Elongate tubular process links cells to form colonies

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...


Stauroforma 1

  1. Valves lack rimoportulae
  2. Striae meet in central valve face
  3. Central area absent

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...


Stauroneis 45

  1. Stauros present
  2. Pseudosepta may be present
  3. Striae distinctly punctate

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....


Staurophora 5

  1. Fascia with short striae at margins
  2. Deep, highly arched valves
  3. Striae composed of small round poroids
  4. Single lobed chloroplast with large pyrenoid

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...


Staurosira 3

  1. Striae narrow, composed of small, round or somewhat elongated areolae
  2. Striae do not meet in central sternum

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...


Staurosirella 4

  1. Striae composed of lineolate areolae
  2. Apical porefield at each pole
  3. Valves elliptical, linear or cruciform

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...


Stenopterobia

  1. Valves long, thin
  2. Symmetry lanceolate or sigmoid
  3. Raphe within a canal
  4. Raphe positioned along entire valve margin

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...


Stephanocyclus

  1. Cell wall comprised of a single layer
  2. Marginal chambers absent

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...


Stephanodiscus 3

  1. Striae radial and organized into fasicles
  2. Spines marginal
  3. Valve face flat or concentrically undulate
  4. Marginal spines may be subtended by marginal fultoportulae

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,...


Surirella 11

  1. Frustules isopolar or heteropolar
  2. Raphe positioned along entire valve margin
  3. Raphe located within a canal, which may be raised above valve surface

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...


Synedra 3

  1. Cells robust, linear to lanceolate with rounded to capitate ends
  2. Striae parallel
  3. Apical porefield present at each pole
  4. Rimoportula present near each apex

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).