SPECIES starting with "s"

 

Sellaphora alastos

  1. Valves broadly linear
  2. Apices obtusely rounded
  3. Central striae widely spaced
  4. Conopea narrow
  5. Central area rectangular

Symmetrical biraphid - Sellaphora alastos has large, broadly linear valves with obtusely rounded apices. The central striae are more widely spaced than more distal striae. The narrow axial and rectangular central areas are bordered by narrow conopea.


Sellaphora americana

  1. Valves broadly linear
  2. Apices obtusely rounded
  3. Striae evenly spaced throughout
  4. Conopea wide
  5. Central area rounded

Symmetrical biraphid - Sellaphora americana has large broadly linear valves with obtusely rounded apices. Wide conopea border the narrow axial area and rounded central area. Central striae and distal striae have about the same spacing.


Sellaphora bacilloides

  1. Valves elliptic
  2. Apices subtly protracted
  3. Valves 30-35 µm in length
  4. Striae 18 in 10 µm in the center, 26 in 10 µm at the ends

Symmetrical biraphid - Sellaphora bacilloides has elliptic valves with bluntly rounded, subtly protracted apices.


Sellaphora bacillum

Diadesmis bacillum
Pinnularia bacillum
Schizonema bacillum

  1. Valves linear-elongate
  2. Length 30-45 µm
  3. Axial area bordered by a distinct, hyaline conopeum

Symmetrical biraphid - Valves are linear-elongate with apices rounded. The axial area is bordered by a distinct, hyaline conopeum. The striae are broadly spaced at the center of the valve and become much finer (to 22 in10 µm) at the ends.


Sellaphora californica

  1. Valves elliptic with rostrate apices
  2. Thin grooves along each side of raphe
  3. Grooves covered by conopea
  4. Central area transversely rectangular or bow-tie-shaped

Symmetrical biraphid - Valves are elliptic with rostrate apices. Valves are 23-40 μm long and 8-10 μm wide. Raphe branches have one very thin groove (1 µm wide) on either side, covered by a conopea. Grooves and conopea are discontinuous at the central area. The striae are strongly radiate, becoming convergent near the apices. The central area is transverse, often bow-tie-shaped and bordered by irregularly shortened striae.


Sellaphora hohnii

  1. Valves elliptic to linear-elliptic with subrostrate apices
  2. Grooves along each side of raphe ~1 μm wide
  3. Grooves covered by conopea
  4. Central area transversely rectangular or bow-tie shaped

Symmetrical biraphid - Valves are elliptic to linear-elliptic with subrostrate apices; 28-47 μm long and 8.9-9.8 μm wide. The grooves are approximately 1 μm wide. The central area is transversely rectangular or bow-tie shaped and bordered by irregular, shortened striae. Striae are radiate, becoming convergent near the apices.


Sellaphora meridionalis

  1. Valves elliptic
  2. Central area bow-tie shaped
  3. Polar bars present

Symmetrical biraphid - Valves are elliptic, with broadly rounded ends that are only very slightly protracted. The central area is bow-tie shaped, bordered alternating short and long striae. At the valve ends, polar bars present. The external surface of the valve face is smooth, without visible grooves or conopea.


Sellaphora pulchra

  1. Valves elliptic-lanceolate with sub-capitate to capitate ends
  2. Central area bow-tie shaped

Symmetrical biraphid - Valves are elliptic-lanceolate with sub-capitate to capitate ends. The central area is bow-tie shaped, bordered by alternating short and long striae. Striae are strongly radiate at the mid-valve, becoming parallel or slightly convergent at the ends. Only a few striae around the central area may be resolved under LM. Polar bars are indistinct or very slightly developed.


Sellaphora rexii

  1. Valves elliptic with subrostrate apices
  2. Grooves along each side of raphe 0.5 μm wide
  3. Grooves covered by conopea
  4. Central area transversely rectangular or bow-tie shaped

Symmetrical biraphid - Valves are elliptic, with subrostrate apices. Valves are 22-33 μm long and 7.1-8.6 μm wide. The axial area is linear, formed by grooves, one at each side of the raphe. Grooves are approximately 0.5 μm wide and covered externally by non-porous conopeum. Grooves and conopea are interrupted by the central area, which is transversely rectangular, or bow-tie-shaped and bordered by striae of an irregular length. Polar bars are present.


Sellaphora subfasciata

Navicula subfasciata

  1. Valves lanceolate, with capitate apices
  2. Central area elliptic or rectangular
  3. Striae are strongly radiate and bent
  4. Polar bars present

Symmetrical biraphid - Valves are lanceolate with capitate apices. The central area is elliptic or rectangular. Striae are strongly radiate and bent. The raphe is filiform, with slightly expanded proximal ends. Polar bars are present.


Sellaphora wallacei

  1. Valves linear
  2. Striae not visible in LM
  3. Central area small
  4. Polar bars present

Symmetrical biraphid - Valves are linear with rostrate to subcapitate ends. Valves are 4.1-4.7 µm wide. The central area is very small. Striae are radiate, and may only be distinguishable near the central area. Polar bars are present at the apices.


Simonsenia delognei

  1. Valve apices extremely narrow, often protracted
  2. Costae 18 in 10 µm

Nitzschioid - The valves of S. delognei have extremely narrow apices that are often protracted. The costa density is 18 in 10 µm.


Spicaticribra kingstonii

  1. Valve face flat
  2. Central areolae larger than marginal areolae
  3. Marginal fultoportulae conspicuous
  4. Areolae coarse

Centric - The valve face is flat, with relatively large, coarse areolae. Striae are radial. Central areolae are larger than the marginal areolae. The marginal fultoportulae are distinct in LM, while the rimoportulae are not distinguishable.


Stauroforma exiguiformis

  1. Apices broadly rounded
  2. Sternum narrow
  3. Spines aligned with costae
  4. Striae on the mantle reduced

Araphid - Valves of S. exiguiformis have broadly rounded ends. The sternum is narrow. Spines are round, hollow and positioned on the costae. Apical pore fields are absent. In girdle view, frustules are rectangular and striae on the mantle are reduced.


Stauroneis absaroka

  1. Axial area broad, often with irregular ends of striae
  2. Broad stauros with curved margins
  3. Proximal raphe ends curved, tipped with drop-like ends
  4. Striae curved near the central area

Symmetrical biraphid - Stauroneis absaroka has lanceolate valves with subrostrate to subcapitate apices. The axial area is broad and often has irregular borders formed by the striae. Proximal raphe ends are distinctly curved and tipped with drop-like ends. Striae are curved on the margins of the broad stauros.


Stauroneis acidoclinata

  1. Valves linear-lanceolate to linear
  2. Apices abrupt, subrostrate to subcapitate
  3. Proximal raphe ends slightly curved

Symmetrical biraphid - Stauroneis acidoclinata has linear-lanceolate to linear valves 35-70 µm long, with abruptly protracted subrostrate to subcapitate apices and curved proximal raphe ends.


Stauroneis acidoclinatopsis

  1. Apices abruptly protracted, capitate
  2. Valves linear-lanceolate
  3. Proximal raphe ends weakly curved and expanded
  4. Stauros rectangular

Symmetrical biraphid - Valves of S. acidoclinatopsis are linear-lanceolate with abruptly protracted, capitate apices. Valves are 10-12 µm wide and greater than 50 µm long. Proximal raphe ends are weakly curved and expanded. The stauros is rectangular.


Stauroneis acuta

  1. Valves large, rhombic-lanceolate with a gibbous central region
  2. Pseudosepta present
  3. Proximal raphe ends straight, weakly expanded
  4. Stauros bow-tie shaped
  5. Striae strongly radiate

Symmetrical biraphid - Stauroneis acuta has large rhombic-lanceolate valves with a gibbous central region, acutely rounded apices with pseudosepta, straight and weakly expanded proximal raphe ends, strongly radiate striae, and a large stauros shaped like a bow tie.


Stauroneis agrestis

  1. Valves linear
  2. Apices capitate
  3. Stauros broad, bow tie shaped
  4. Striae strongly radiate
  5. Proximal raphe ends straight

Symmetrical biraphid - Stauroneis agrestis has linear valves 23-27 µm long with capitate apices. Proximal raphe ends are straight. The stauros is broad and shaped like a bow tie. Striae are strongly radiate and number near 40 in 10 µm.


Stauroneis akamina

  1. Areolae oblong and irregularly spaced
  2. Valves lanceolate, large
  3. Apices rostrate to subcapitate
  4. Proximal raphe ends straight

Symmetrical biraphid - Stauroneis akamina has oblong areolae that are irregularly spaced. Valves are lanceolate and range from 63 to 140 µm long. Apices are rostrate to subcapitate. Proximal raphe ends are straight and not expanded.


Stauroneis americana

  1. Valves large
  2. Pseudosepta present
  3. Proximal raphe ends straight
  4. Stauros rectangular
  5. Striae slightly radiate

Symmetrical biraphid - Stauroneis americana has large, broadly lanceolate valves with bluntly-rounded apices and prominent pseudosepta. The proximal raphe ends are straight and weakly expanded. The striae are slightly radiate.


Stauroneis amphicephala

  1. Valves linear-elliptic-lanceolate
  2. Apices rostrate to subcapitate
  3. Stauros bow-tie shaped

Symmetrical biraphid - Stauroneis amphicephala is a moderately large Stauroneis species with linear-elliptic-lanceolate valves that are wider than 11 µm. The apices are protracted and rostrate, to subcapitate. The stauros is wider at the valve margins forming a bow-tie shape.


Stauroneis anceps

  1. Apices protracted and narrowly rostrate
  2. Valves lanceolate to linear-lanceolate
  3. Stauros narrow and rectangular

Symmetrical biraphid - Stauroneis anceps has moderately large lanceolate to linear-lanceolate valves, 12-15 µm wide. The apices are distinctly protracted, narrow and rostrate. The stauros (in specimens from the Northern Rockies) is relatively narrow and rectangular. Proximal raphe ends are weakly expanded and deflected.


Stauroneis ancepsfallax

  1. Apices capitate
  2. Valves lanceolate
  3. Stauros bow tie shaped
  4. Proximal raphe ends straight, weakly expanded

Symmetrical biraphid - Stauroneis ancepsfallax has lanceolate valves with capitate apices. The valves are 11-14 µm wide. The stauros is distinctly expanded toward the valve margins and shaped like a bow tie. Proximal raphe ends are nearly straight and weakly expanded.


Stauroneis angustilancea

  1. Valves lanceolate
  2. Apices narrow, subrostrate
  3. Striae 15-20 in 10 µm
  4. Areolae 14-20 in 10 µm

Symmetrical biraphid - Stauroneis angustilancea has lanceolate valves up to 125 µm long. Valve apices are narrow and subrostrate. Striae are radiate and number 15-20 in 10 µm. Areolae are relatively coarse and number 14-20 in 10 µm.


Stauroneis baconiana

Stauroneis nobilis var. baconiana

  1. Areolae oblong and irregularly spaced
  2. Valves linear-lanceolate, 73-139 µm long
  3. Apices long, protracted
  4. Proximal raphe ends straight

Symmetrical biraphid - Stauroneis baconiana has transversely oblong and irregularly spaced areolae. The valves are linear-lanceolate and measure 73-139 µm long. The apices are long, protracted and rostrate. Proximal raphe ends are straight and not expanded.


Stauroneis beeskovea

  1. Striae strongly radiate
  2. Valves narrowly lanceolate
  3. Apices subtly protracted
  4. Raphe filiform near apices
  5. Stauros somewhat wider at valve margins

Symmetrical biraphid - Stauroneis beeskovea has strongly radiate striae. The valves are narrowly lanceolate with subtly protracted, broadly rounded apices. Proximal raphe ends are straight and simple. Raphe branches are filiform near the terminal fissures. The stauros is somewhat wider at the valve margins and often has 1-3 short striae on each side.


Stauroneis boyntoniae

  1. Valves broadly lanceolate
  2. Apices narrow subrostrate to apiculate
  3. Areolae elongated and irregular

Symmetrical biraphid - Stauroneis boyntoniae has broadly lanceolate valves, 31-52 µm long. The apicies are narrow and subrostrate to apiculate. Areolae are transapically elongated and irregularly spaced.


Stauroneis bryocola

  1. Valves lanceolate
  2. Apices subtly rostrate and broadly rounded
  3. Areolae fine

Symmetrical biraphid - Stauroneis bryocola has lanceolate valves with subtly protracted and broadly rounded rostrate apices. Areolae are fine and number 24-30 in 10 µm.


Stauroneis circumborealis

  1. Valves large, elliptic-lanceolate
  2. Apices short and broadly rounded
  3. Axial area 4-5 times wider than raphe
  4. Stauros wide
  5. Proximal raphe ends strongly curved

Symmetrical biraphid - Stauroneis circumborealis has large elliptic-lanceolate valves with short, broadly rounded apices. The axial area is 4-5 times wider than the raphe and the stauros is wide. Proximal raphe ends are strongly curved.


Stauroneis conspicua

  1. Valves lanceolate to elliptic-lanceolate, up to 24 µm wide
  2. Apices subrostrate to subcapitate
  3. Proximal raphe ends nearly straight and slightly dilated

Symmetrical biraphid - Valves are large, lanceolate to elliptic-lanceolate, up to 24 µm wide. Valve apices are subrostrate to subcapitate. Proximal raphe ends are nearly straight and slightly dilated.


Stauroneis finlandia

  1. Valves broadly lanceolate
  2. Pseudosepta present
  3. Proximal raphe ends strongly curved

Symmetrical biraphid - Stauroneis finlandia has large lanceolate valves with subrostrate apices and prominent pseudosepta. The proximal raphe ends are strongly curved and expanded. The width may be greater than 30 µm.


Stauroneis fluminopsis

  1. Valves large, linear-lanceolate
  2. Apices subrostrate
  3. Stauros narrow, nearly rectangular
  4. Proximal raphe ends straight, weakly inflated
  5. Striae and areolae fewer than 19 in 10 µm

Symmetrical biraphid - Valves are large linear-lanceolate with subrostrate apices. The stauros is narrow and nearly rectangular. Proximal raphe ends are straight and weakly inflated. Striae and areolae are fewer than 19 in 10 µm.


Stauroneis gracilis

  1. Valves elliptic-lanceolate
  2. Apices subrostrate, broadly rounded
  3. Proximal raphe ends curved, expanded
  4. Areolae 18-22 in 10 µm

Symmetrical biraphid - Stauroneis gracilis has elliptic-lanceolate valves that are 68 to 127 µm long. The apices are subrostrate and broadly rounded. Proximal raphe ends are curved and expanded. Areolae number 18-22 in 10 µm.


Stauroneis heinii

  1. Valves large, lanceolate
  2. Apices subrostrate
  3. Axial area 3 times wider than raphe
  4. Stauros moderately wide
  5. Proximal raphe ends somewhat curved, dilated

Symmetrical biraphid - Stauroneis heinii has large lanceolate valves with subrostrate apices. The axial area is about three times wider than the raphe and the central area is moderately wide. Proximal raphe ends are somewhat curved and dilated.


Stauroneis kingstonii

  1. Valves narrow
  2. Apices acutely rounded
  3. Axial area broad

Symmetrical biraphid - Valves are narrow and elongate, with acutely rounded apices. Valves have a broad axial area and a bowtie shaped stauros. Striae number 11-13 in 10 µm and areolae number 16-20 in 10 µm.


Stauroneis kishinena

  1. Valves broadly lanceolate, width up to 33 µm
  2. Pseudosepta present
  3. Proximal raphe ends strongly curved
  4. Striae 11-12 in 10 µm
  5. Apices not protracted

Symmetrical biraphid - Stauroneis kishinena has large, broadly lanceolate valves without protracted apices. Pseudosepta are present. Proximal raphe ends are strongly curved and expanded. Striae are widely spaced and number 11-12 in 10 µm.


Stauroneis kootenai

  1. Valves lanceolate
  2. Apices capitate
  3. Areolae easily resolved in LM

Symmetrical biraphid - Valves are lanceolate, 34-52 µm long. The apices are capitate. Areolae are easy to resolve in LM.


Stauroneis kriegeri

  1. Valves linear-lanceolate
  2. Apices subcapitate
  3. Stauros narrow, nearly rectangular
  4. Striae radiate
  5. Proximal raphe ends straight

Symmetrical biraphid - Stauroneis kriegeri has linear-lanceolate valves with subcapitate apices and a relatively narrow, nearly rectangular stauros. Striae are radiate throughout and proximal raphe ends are straight and not expanded.


Stauroneis lauenburgiana

  1. Valves linear to linear-elliptic
  2. Areolae coarse
  3. Areolae form longitudinal lines along axial area
  4. Pseudosepta present

Symmetrical biraphid - Stauroneis lauenburgiana has linear to linear-elliptic valves less than 50 µm long. Shallow pseudosepta are present. Areolae are coarse, transversely oblong and irregularly spaced. Areolae form an uninterrupted longitudinal line along each side of the axial area.


Stauroneis livingstonii

  1. Valves linear-elliptic, 6.6-8.6 µm wide
  2. Apices narrow, rostrate, with pseudosepta
  3. Striae radiate throughout

Symmetrical biraphid - Valves are linear-elliptic, 6.6 to 8.6 µm wide. Apices are narrow, rostrate, and with pseudosepta. Striae are radiate throughout.


Stauroneis neohyalina

  1. Valves linear-lanceolate
  2. Apices narrow, rostrate to subcapitate
  3. Areolae >30 in 10 µm

Symmetrical biraphid - Valves are linear-lanceolate with narrow rostrate to subcapitate apices. The striae and areolae are very fine and exceed 30 in 10 µm.


Stauroneis pax

  1. Valves linear-lanceolate
  2. Apices subcapitate
  3. Stauros bow tie shaped
  4. Striae strongly radiate
  5. Striae short at central area margin

Symmetrical biraphid - Stauroneis pax has linear-lanceolate valves with subcapitate apices. The stauros is wide at the valve margins and shaped like a bow tie. One to several short striae are present at the margins of the central area. The striae are strongly radiate and are not straight.


Stauroneis phoenicenteron

  1. Valves lanceolate and large, up to 35 microns wide
  2. Apices rounded
  3. Proximal raphe ends straight
  4. Striae 15-18 in 10 µm

Symmetrical biraphid - Stauroneis phoenicenteron has large lanceolate valves with rounded ends. Proximal raphe ends are straight. Striae are moderately coarse, but no fewer than 15 in 10 µm.


Stauroneis pikuni

  1. Valves lanceolate to rhombic-lanceolate
  2. Apices capitate
  3. Striae continuous next to central area
  4. Areolae round to transapically oblong

Symmetrical biraphid - Stauroneis pikuni has rhombic-lanceolate valves 53-64 µm long, with capitate apices. Striae are continuous near the central area, that is, hyaline areas are lacking.The areolae are round to transapically oblong and irregularly spaced.


Stauroneis pseudagrestis

  1. Valves lanceolate
  2. Apices capitate
  3. Stauros relatively large
  4. Striae strongly radiate
  5. Proximal raphe ends bent

Symmetrical biraphid - Stauroneis pseudagrestis has lanceolate valves with capitate apices and a large stauros with curved margins. The striae are strongly radiate and proximal raphe ends are bent slightly to the same side.


Stauroneis reichardtii

  1. Valves nearly linear, sides nearly parallel
  2. Apices capitate
  3. Stauros shaped like a bow tie
  4. Proximal raphe ends straight and weakly expanded

Symmetrical biraphid - Valves are linear-elliptic to linear-lanceolate with nearly parallel sides and abruptly protracted and distinctly capitate apices. The stauros is relatively broad and shaped like a bow tie. The axial area is narrow and linear. The proximal raphe ends are straight and weakly expanded.


Stauroneis rex

  1. Valves very large
  2. Striae coarse, 12-14 in 10 µm
  3. Proximal raphe ends straight
  4. Apices bluntly rounded

Symmetrical biraphid - Stauroneis rex is huge: 36-60 µm wide and 215-386 µm long. Valves are lanceolate with bluntly rounded apices. Proximal raphe ends are straight. Striae are coarse and number 12-14 in 10 µm.


Stauroneis sacajaweae

  1. Valves lanceolate
  2. Apices subrostrate
  3. Pseudosepta present
  4. Proximal raphe ends bent to one side
  5. Striae 23-25 in 10 μm

Symmetrical biraphid - Stauroneis sacajaweae has medium-sized lanceolate valves (10-15 μm wide) with subrostrate apices and a pseudoseptum under each apex. Proximal raphe ends are bent to the same side. Striae number 23-25 in 10 μm.


Stauroneis schroederi

  1. Valves lanceolate
  2. Apices narrow, rostrate to subcapitate
  3. Areolae 22-28 in 10 µm

Symmetrical biraphid - Valves are lanceolate with narrow rostrate to subcapitate apices. Areolae are fine and number 22-28 in 10 µm.


Stauroneis separanda

  1. Valves triundulate
  2. Pseudosepta present
  3. Apices rostrate-apiculate

Symmetrical biraphid - Stauroneis separanda has triundulate valves, less than 20 µm long with rostrate-apiculate apices. A pseudoseptum is present at each valve apex.


Stauroneis siberica

  1. Valves lanceolate to elliptic-lanceolate
  2. Apices rostrate to subcapitate
  3. Areolae very fine
  4. Areolae bordering stauros coarse
  5. Stauros narrower toward valve margins

Symmetrical biraphid - Stauroneis siberica has lanceolate to elliptic-lanceolate valves with rostrate to subcapitate apices. The striae are very fine and number 24-32 in 10 µm. The stauros is typically narrower toward the valve margins and may, or may not, contain short striae. Areolae bordering the stauros are more prominent and more widely spaced than areolae elsewhere.


Stauroneis smithii

  1. Valves triundulate, small
  2. Apices short, apiculate
  3. Pseudosepta present
  4. Stauros narrow, linear

Symmetrical biraphid - Stauroneis smithii has small valves with triundulate margins and short apiculate apices. Pseudosepta are present. The stauros is narrow and linear.


Stauroneis sonyae

  1. Valves large, elliptic-lanceolate
  2. Apices narrow, subrostrate
  3. Axial area 3-4 times wider than raphe
  4. Stauros wide, bow tie shaped
  5. Proximal raphe ends curved and strongly dilated

Symmetrical biraphid - Stauroneis sonyae has large elliptic-lanceolate valves with narrow subrostrate apices. The axial area is 3-4 times wider than the raphe. The stauros is very wide, shaped like a bow tie, and usually with short striae at the margins. Proximal raphe ends are curved and strongly dilated.


Stauroneis subborealis

  1. Valves linear in small specimens, lanceolate in large specimens
  2. Apices protracted and broadly rounded
  3. Proximal raphe ends curved, inflated
  4. Striae 17-20 in 10 µm
  5. Areolae 18-22 in 10 µm

Symmetrical biraphid - The small specimens are linear, while large specimens are lanceolate; 46-142 µm in length. Apices are protracted and broadly rounded. Proximal raphe ends are curved and inflated. Striae are radiate throughout and number 17-20 in 10 µm. Areolae number 18-22 in 10 µm.


Stauroneis submarginalis

  1. Valves broadly lanceolate, 140-186 µm long
  2. Longitudinal submarginal line near valve/mantle junction
  3. Apices slightly protracted
  4. Proximal raphe ends curved

Symmetrical biraphid - Stauroneis submarginalis has broadly lanceolate valves, 140 to 186 µm long, with slightly protracted and broadly rounded apices. A distinct longitudinal line, visible in LM, runs the length of the valve 2-3 µm inside the valve margins. Proximal raphe ends are curved.


Stauroneis supergracilis

  1. Valves narrowly lanceolate
  2. Apices subtly protracted
  3. Proximal raphe ends curved and inflated
  4. Areolae 14-18 in 10 µm

Symmetrical biraphid - Stauroneis supergracilis has large, narrowly lanceolate valves, 124-213 µm long, with subtly protracted apices. Proximal raphe ends are curved and inflated. Areolae are relatively coarse and number 14-18 in 10 µm.


Stauroneis superkuelbsii

  1. Areolae next to stauros extremely elongated
  2. Valves lanceolate to linear-lanceolate, 80-156 µm long
  3. Areolae coarse

Symmetrical biraphid - Stauroneis superkuelbsii has large lanceolate to linear-lanceolate valves that are 80 to 156 µm long. Areolae are somewhat transapically elongate and number 13 to 17 in 10 µm. Areolae adjacent to the central fascia are extremely transapically elongate.


Stauroneis thompsonii

  1. Valves lanceolate
  2. Pseudosepta present
  3. Proximal raphe ends straight
  4. Striae 15-18 in 10 µm

Symmetrical biraphid - Stauroneis thompsonii has lanceolate valves, 16-24 µm wide, with a pseudoseptum at each apex. Striae number 15-18 and areolae 12-16 in 10 µm.


Stauroneis vandevijveri

  1. Valves lanceolate
  2. Apices rostrate to subcapitate
  3. Stauros broad
  4. Proximal raphe ends straight
  5. Axial area narrow and linear

Symmetrical biraphid - Stauroneis vandevijveri has lanceolate valves with rostrate to subcapitate apices. The axial area is narrow and linear; the stauros is broad and shaped like a bow tie. External proximal raphe ends are straight and not expanded.


Staurophora brantii

  1. Valves rhombic-lanceolate, 38-48 μm long
  2. Apices broadly rounded and subtly protracted
  3. Central area wider toward margins

Symmetrical biraphid - Staurophora brantii has rhombic-lanceolate valves 38-48 μm long. The apices are indistinctly protracted and broadly rounded. The central area is a relatively broad transverse fascia that widens in deltoid fashion towards the valve margins. Unlike species of Stauroneis, Staurophora brantii has a single lobed chloroplast and prefers waters with elevated electrolytes (see Autecology).


Staurophora columbiana

  1. Valves linear-lanceolate to elliptic-lanceolate
  2. Central area small

Symmetrical biraphid - Valves are linear-lanceolate to elliptic-lanceolate, 35-54 µm long. The central area is small (except in Janus valves) and lacks a distinct transverse fascia.


Staurophora soodensis

Stauroneis soodensis
Dickieia soodensis

  1. Valves bluntly rounded at apices
  2. Central transverse fascia narrow
  3. Striae 16-20 in 10 µm

Symmetrical biraphid - Staurophora soodensis has apices that are bluntly rounded. The central transverse fascia is narrow. Striae number 16-20 in 10 µm.


Staurophora tackei

Stauroneis tackei

  1. Valves linear-lanceolate, up to 30 µm long
  2. Apices broadly rounded
  3. Striae fine, 20-30 in 10 µm
  4. Central area a rectangular fascia

Symmetrical biraphid - Valves are linear-lanceolate, up to 30 µm long, with broadly rounded apices. The central area is a rectangular fascia. Striae are fine and weakly radiate. Areolae are difficult to resolve in LM. Unlike species of Stauroneis, species of Staurophora have a single lobed chloroplast (not shown) and a preference for waters with elevated electrolytes.


Staurophora wislouchii

  1. Valves elliptical to elliptic-lanceolate, 25-40 µm long
  2. Apices short protracted and broadly rounded
  3. Striae fine, 24-30 in 10 µm
  4. Central area a rectangular fascia

Symmetrical biraphid - Valves are elliptic to elliptic-lanceolate, 25-40 µm long, with short protracted and broadly rounded apices. Striae are parallel in the center to weakly radiate towards the ends and number 24-30 in 10 µm. The central area is a rectangular fascia. Areolae are difficult to resolve in LM. Unlike species of Stauroneis, species of Staurophora have a single lobed chloroplast (not shown) and a preference for waters with elevated electrolytes.


Staurosira construens

  1. Valves cruciform
  2. Striae alternate
  3. Striae in valve center curved
  4. Apical pore fields present
  5. Spines hollow

Araphid - Valves of S. construens are cruciform in outline. Striae from each side of the valve do not meet in the center, they are alternate. Striae near the middle part of the valve may be curved. Apical pore fields are present and are composed of poroids surrounded by a whitish rim. Spines are present, located between the striae. Spines are hollow and spatulate.


Staurosira construens var. binodis

  1. Valves bi-undulate
  2. Axial area linear to lanceolate
  3. Apical pore fields present
  4. Spines hollow

Araphid - Valves at the larger end of the size range of S. construens var. binodis are bi-undulate, while smaller specimens are lanceolate to cruciform. The axial area is linear to slightly lanceolate. Two apical pore fields are present on the valve mantle. Under the SEM, the apical porefields are found to be composed of round poroids. Spines are hollow, spatulate and located between striae.


Staurosira construens var. venter

  1. Valves lanceolate
  2. Axial area lanceolate
  3. Spines hollow

Araphid - Valves of S. construens var. venter are lanceolate, becoming elliptical in smaller specimens. Spines are hollow, spatulate, and positioned between striae.


Staurosirella leptostauron

Fragilaria leptostauron

  1. Valves cruciform
  2. Striae wide
  3. Spines positioned on costae

Araphid - Valves of S. leptostauron are cruciform with rounded ends. Striae are wide, formed by lineolate striae. Costae are narrower than striae. Spines are flat near the base, and spatulate toward the ends. Spines are solid and positioned on the costae. Two distinct porefields are present at each apex. Girdle bands are closed and lack perforations; the valvocopulum (first girdle band) is wider than other girdle elements and bears fimbriae.


Staurosirella leptostauron var. dubia

Fragilaria leptostauron var. dubia

  1. Valves lanceolate to elliptical
  2. Areolae lineolate
  3. Costae wider than striae
  4. Spines reduced, two per costae

Araphid - Valves of S. leptostauron var. dubia are lanceolate to elliptical with rounded ends in smaller specimens. The distinct, broad striae are composed of lineolate areolae. Costae tend to be wider than striae. Spines are solid and reduced compared to other Staurosirella taxa. Two spines are present for each costa.


Staurosirella martyi

Martyana martyi
Fragilaria martyi

  1. Valves may be heteropolar or isopolar
  2. Valves coarse
  3. Areolae lineolate
  4. Apical pore field present at footpole

Araphid - Valves are coarse and variable in outline; they may be heteropolar to isopolar. The striae are composed of lineolae and appear coarse, refractive and distinctive. A single apical porefield is present at the footpole. A “step” at the headpole may be present or absent. Spines are absent.


Staurosirella pinnata

  1. Valves oval
  2. Areolae lineolate
  3. Costae with spines

Araphid - Striae are composed of pronounced lineolate areolae; costae are narrow. Solid spines are positioned on the costae. In the SEM, spines are conical at the base, becoming spatulate near the terminus. Porefields are absent. Girdle bands are open and lack perforations.


Staurosirella rhomboides

Fragilaria leptostauron var. rhomboides
Staurosirella leptostauron var. rhomboides

  1. Valves rhomboid
  2. Striae as wide
  3. Spines flat, positioned on costae

Araphid - Valves are rhomboid with rounded ends. Striae are wide, formed by lineolate areolae. Spines are flat, solid and positioned on the costae. Two distinct porefields are present at each apex. The headpole porefield is larger than the footpole porefield.


Stephanodiscus alpinus

  1. Valves small
  2. Fascicles uniseriate to biseriate at margin
  3. Areolae relatively coarse
  4. Marginal spine on every interfascicle
  5. Areolae in central area disorganized

Centric - Valves are less than 33 µm in diameter with a marginal spine on every interfascicle. Areolae are relatively coarse and arranged in fascicles that are uniseriate near the valve center to biseriate near the valve margin. Areolae in the central area are disorganized.


Stephanodiscus niagarae

  1. Valves concentrically undulate
  2. Areolae round
  3. Areolae 11-20 in 10 µm
  4. Marginal spines placed every 2-3 costae

Centric - Valves are concentrically undulate, so that only the valve margin or the valve center is in focus at one time. The areolae are round and arranged in fascicles of radial striae, separated by raised costae. Areolae are 11-20 in 10 µm. Striae are uniseriate in the center valve and biseriate near the margin. Marginal spines are present. Marginal fultoportulae are present, positioned below the spines. Central fultoportulae are also present in the valve center, singly or in a ring. One or more rimoportulae are present near a marginal spine, with a spine-like external extension.


Stephanodiscus oregonicus

Cyclotella oregonica

  1. Valves small
  2. Concentric undulation distinct
  3. Fascicles multiseriate at valve margin
  4. Central areolae disorganized or weakly radiate
  5. Marginal spine on every interfascicle

Centric - Valves are small, at less than 40 µm in diameter. Fascicles are multiseriate at the valve margin, where they are always composed of 3 or more rows of areolae. The valve face has strong concentric undulation, with either a convex or concave central area. The aeolae in the central area are disorganized or arranged in weakly radiate rows. A marginal spine is present on every interfascicle.


Stephanodiscus reimeri

  1. Valves large, robust
  2. Areolae trapezoidal to sub-hexagonal
  3. Radial areolae 8-12 in 10 µm
  4. Marginal spines spaced every 2-3 costae

Centric - Valves are disc-shaped with a concentrically undulate face. Areolae are large, trapezoidal to sub-hexagonal in shape and arranged in fascicles that radiate outward from the valve center. Areolae along the radius number 8-12 in 10 µm. Marginal spines are located at the end of every two to three costae, just inside the valve face margin.


Stephanodiscus yellowstonensis

  1. Valves concentrically undulate
  2. Areolae round
  3. Areolae 12-18 in 10 µm
  4. Marginal spines every 2-5 costae

Centric - Valves are concentrically undulate; only the valve margin or the valve center is in focus at one time. The areolae are round and arranged in fascicles of radial striae, separated by costae. Areolae are 12-18 in 10 µm. Striae are uniseriate in the center valve and multiseriate (2-5) near the margin. Marginal spines are present, positioned every 2-5 costae. Marginal fultoportulae are present, positioned below the spines. Central fultoportulae are also present in the valve center, singly or in a ring. One or more rimoportulae are present near a marginal spine, with a spine-like external extension.


Surirella amphioxys

Surirella biseriata f. amphioxys

  1. Keel low, alar wings absent
  2. Valves isopolar
  3. Valve face with undulations (porca)
  4. Striae 16-20 in 10 µm
  5. Valves 28-48 µm long, by 13.5-17 µm wide

Surirelloid - Valves are 28-48 µm long by 13.5-17 µm wide, isopolar with cuneate apices. The valve face has undulations, or porca, that appear as rectangles in the LM. Striae are 16-20 in 10 µm.


Surirella angusta

Surirella ovalis var. angusta
Surirella ovata var. angusta
Surirella ovalis var. angusta

  1. Keel low, alar wings absent
  2. Valves isopolar
  3. Striae 23-28 in 10 µm
  4. Each 3rd or 4th costae raised
  5. Valve face flat

Surirelloid - The keel is low, no alar wings are visible. Valves are isopolar with a flat valve face. Striae are dense, 23-24 in 10 µm. Each third or fourth costae is raised; costae number 7-8 in 10 µm. Valves are 15.5-60 µm long by 6.5-12 µm wide.


Surirella atomus

  1. Keel low, alar wings absent
  2. Valves small
  3. Valves heteropolar
  4. Fibulae broad and short
  5. Costae and central line not visible in LM

Surirelloid - Valves are small and heteropolar, 8-19 μm long by 5-8 μm wide. Headpole is broadly rounded and foopole is cuneately rounded. Fibulae are broad and short, 8-10 in 10 μm. Costae and center line are not visible in the LM.


Surirella brebissonii

  1. Keel low, alar wings absent
  2. Valves large, heteropolar
  3. Valves with large size range
  4. Fibula density 5-6 in 10 µm
  5. Costa density 18-23 in 10 µm

Surirelloid - Valves with large size range, 15.5-56.0 µm in length and 10-25 µm in width. Smaller valves are almost circular, but larger valves have one broadly rounded apex and one cuneately rounded apex. Costa density is 18-23 in 10 µm and fibula density is 5-6 in 10 µm.


Surirella cruciata

  1. Valve with cuneate footpole and broadly rounded headpole
  2. Central part of valve distinctly raised
  3. Central porcae distinct
  4. Axial area narrow, elevated in a keel

Surirelloid - Valves are obovoid with cuneate footpole and broadly rounded headpole. Larger specimens are distinctly heteropolar. The valve face is distinctly and abruptly raised in the central third of the valve. Porcae are pronounced in the central part of valve, arranged in an opposite to alternate pattern. The axial area is narrow, lacks ornamentation and is elevated in a shallow keel. The alar canals are narrower than the fenestrae, usually even in density throughout.


Surirella iowensis

  1. Keel low, alar wings absent
  2. Valves heteropolar
  3. Valves slightly twisted about the apical axis
  4. Valves 21-54 μm long, 15-33 μm wide
  5. Fibulae 6-8 in 10 μm

Surirelloid - Valves are heteropolar, with a broadly rounded headpole and a cuneately rounded footpole in the larger valves and a broadly rounded footpole in the smaller valves. The valve face is slightly concentrically undulate and twisted about the apical axis. Fibulae are 6-8 in 10 μm and costae are 16-26 in 10 μm.


Surirella minuta

Surirella ovalis var. minuta
Surirella ovata var. minuta
Surirella pinnata var. minuta

  1. Keel low, alar wings absent
  2. Valves slightly heteropolar
  3. Valve sides straight, tapering toward footpole
  4. Each 3rd or 4th costa raised
  5. Fibulae extend from the mantle almost to axial line

Surirelloid - The valves are slightly heteropolar with rounded apices and 18-71 µm long by 8.5-14 µm wide. Valve sides are straight, tapering toward the narrower pole (footpole). Fibulae extend from the mantle almost to the axial line, in a density of 9-12 per 10 μm. The costae are dense, 25-32 per 10 µm and every 3rd or 4th costa is raised.


Surirella ovalis

Surirella ovata var. ovalis
Suriraya ovalis

  1. Keel low, alar wings absent
  2. Valves large, heteropolar
  3. Valve length 14-75 µm, width 11-35 µm
  4. Fibula density 5-6 in 10 µm
  5. Costa density 14-17 in 10 µm

Surirelloid - Valves are extremely variable in size and outline, 14-75 µm long by 11-35 µm wide. The larger valves have cuneately rounded apices, while the smaller valves have two broadly rounded apices. Mid-sized specimens have one broadly rounded apex and one cuneately rounded apex. The costae number 14-17 in 10 µm and every third or fourth costa is raised above the others. The fibulae are marginal, 5-6 in 10 µm.


Surirella stalagma

  1. Valves small
  2. Valves heteropolar
  3. Costae not visible in LM
  4. Fibulae short, wide
  5. Low keel, wider than the mantle

Surirelloid - Valves are small and heteropolar, 11-16 µm long by 5-7 µm wide. The foot-pole is capitate, while the head-pole is rounded. The costae are numerous, 55 in 10 µm, so they are only visible in SEM. The fibulae are short and wide, with a density of 8-10 in 10 µm. The keel is low, and broad compared the the mantle.


Surirella suecica

  1. Keel low, alar wings absent
  2. Valves 14-34 µm long, 7-9.5 wide
  3. Costa density high
  4. Valves narrow, clavate
  5. Fibulae short

Surirelloid - Valves are heteropolar, narrow and clavate, with size ranges of 14-34 µm long and 7-9.5 µm wide. The density of costae is high (30-36 in 10 µm), so costae may not be visible in LM. Fibulae are short, and number 9-12 in 10 µm.


Surirella terryi

  1. Valves with slight twist in apical axis
  2. Valves linear, slightly heteropolar
  3. Valves large
  4. Porcae nearly as wide as fenestrae
  5. Axial area thickened, narrow

Surirelloid - Valves are large, linear and slightly heteropolar with rounded cuneate ends. Valves are typically moderately, to distinctly, twisted along the apical axis. The valve length is much more variable (67–176 μm) than the valve width (23–35 μm). The axial area is very narrow and thickened. Valves are distinctly corrugated, with alternate to opposite porcae within a single valve. Alar canals appear about as wide as fenestrae, 16–25 in 100 μm.


Synedra cyclopum

Fragilaria cyclopum

  1. Valves arcuate
  2. Central area not swollen
  3. Apices subcapitate

Araphid - Synedra cyclopum has arcuate valves with gradually attenuated subcapitate apices and the central area lacks a unilateral swelling.


Synedra famelica

  1. Valves very narrow
  2. Valve middle linear
  3. Central area ovoid
  4. Areolae coarse

Araphid - Synedra famelica has very narrow linear valves. The central area is ovoid and often offset to one side. Areolae are coarse and easily resolved in LM.


Synedra mazamaensis

Fragilaria mazamaensis

  1. Valves lanceolate with attenuate, capitate ends
  2. Central area asymmetrical
  3. Central margin of valve swollen

Araphid - Valves are lanceolate with attenuate, capitate ends. The central valve margin is asymmetrically swollen. The central area is asymmetical.