Photos shown are from: BDC ---- Big Darby Creek, http://www.bgsu.edu/departments/biology/algae/html/Darby.html
PGESF ---- Proctor and Gamble Experimental Stream Facility, http://www.bgsu.edu/departments/biology/algae/html/ImageArchive.html
EMI ---- Electron Microscope Images http://www.bgsu.edu/departments/biology/algae/html/SEM.html
1. Cells centric, circular to oval in valve view; short rectangular in girdle view
1. Cell mostly pennate not circular in valve view
Centric Diatoms (diag), Pennate diatoms (diag)
2. Plants filamentous
2. Plant cells isolated or in non-filamentous clusters
Filamentous (diag), Non- filamentous (diag)
3. Cell with one end distinctly different from the other
3. Cells with both ends essentially alike
different (diag) alike (diag)
4. Cell sigmoid in one view
4. Cell not sigmoid in either valve or girdle view
Sigmoid ( picture ), Not sigmoid (picture)
5. Cell longitudinally unsymmetrical in at least one view
5. Cells longitudinally symmetrical
unsymmetrical (picture), symetrical (picture)
6. Longitudinal line (raphe) and prominent marginal markings near both edges of valves
6. Raphe or pseudoraphe not marginal but nearly median Raphe marginal (pict), raphe median (pict)
7. Cells in a thread attached end to end
7. Cells in a thread attached side to side or by their corners
Cells attached end to end, Cells attached side by side
8. Cells often attached at the corners (girdle view)
8. Cells attached side by side, but not at the corners
9. Cells curved in girdle view
9. Cells not curved in girdle view
10. Cells with both fine and coarse transverse lines --- Meridion circulare
10. Transverse lines, if present, all alike in thickness
11. Cells essentially linear to rectangular; one terminal swelling larger than the other (Asterionella)
11. Cells wedge-shaped, egg-shaped or with a wavy nargin
12. Cells wedge-shaped; margins sometimes wavy; raphe central (Gomphonema)
12. Cells egg-shaped; raphe marginal, not visible ---- (Surirella)
13. Diatoms centric, girdle view elongated, often filamentous
13. Centric diatoms usually viewed in valve view because the girdle view is not elongated
14. Cells mostly oval in valve view
14. Cells circular
15. Valve surface with an inner and outer (marginal) pattern of striations P (Cyclotella)
15. Valve surface with one continuous pattern of striae (Stephanodiscus)
16. Cells flat, short oval; not elliptical
16. Cells neither flat nor oval
17. Striae fine, difficult to see; very small, length less than 15m --- Achnanthes hustedii
17. Striae easily visible
18. Wide clear central longitudinal region with many fine longitudinal lines; length 35-85m ---- Amphora ovalis
18. Narrow central region, raphe present
19. Cell sigmoid in valve view
19. Cell sigmoid in girdle view; length 15-150m --- Nitzschia icicularis
20. Cells lacking striations except at margins - Nitzschia obtusa
20. Cells with noticeable striations with oil immersions
21. Striations transverse and longitudinal ----- Gyrosigma
21. Striations oblique (at an angle) - Pleurosigma
22. Cell wall with both fine and transverse lines (striae and costae)
22. Cell wall with fine transverse lines (striae) only
23. Valve face about as wide as girdle face -- Epithemia turgida
23. Valve face one-half or less at the middle as girdle face --- Rhopalodia gibba
24. Line of pores and raphe located at the edge of valve face
24. Raphe not at extreme edge of valve face
25. Raphe of each valve (theca) adjacent to the same girdle surface --- Hantzschia amophioxa
25. Raphe of each valve adjacent to a different girdle surface (Nitzschia)
26. Cell longitudinally unsymmetrical in valve view
26. Cells longitudinally unsymmetrical in girdle view (bent in a shallow V); some may have one-half a clear central area (Achnanthes)
27. Raphe bent toward one side at the middle Amphora ovalis
27. Raphe a smooth curve throughout (Cymbella)
28. Margin of girdle face wavy; often peanut shaped in valve view; large -- Cymatopleura solea
28. Margin of girdle face not wavy; valve view not peanut shaped (Surirella)
29. Girdle face generally in view and with two or more short prominent longitudinal lines. In valve view, swollen central oval portion bounded by a line ,P --- (Tabellaria)
29. Girdle face with less than two prominent longitudinal lines and no thick short ones. In valve view, whole central portion not bounded by a line
30. Valve face with both coarse and very fine transverse lines; often seen in girdle view attached at the corners --- Diatoma vulgare
30. Valve face with transverse lines, if visible, alike in thickness; not normally attached at the corners ---
31. Valve face naviculoid (boat shaped); true raphe present
31. Valve face linear to linear lanceolate; true raphe not present
32. Valve face with wide (coarse) transverse lines or costae (Pinnularia) P
32. Valve face with thin transverse lines (striae)
33. Transverse striae absent across transverse axis of valve face; length 70-380m ---- Stauroneis rhoenicentron P, Fe, pH = 6.0-8.2
33. Transverse striae present across transverses axis of valve face
34. Raphe strictly median
34. Raphe located slightly to one sides
35. Clear central area on both sides of raphe (Navicula) P
35. Clear central area on only one side of raphe (Achnanthes)
36. Knob at one end larger than at the other ---- (Asterionella)
36. Terminal knobs, if present, equal in size (Synedra) A number of species of Synedra may be asymmetrical