Pteroncola, R.W.Holmes & D.A.Croll, 1984

Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H., Khiyami, M. A., Obaid, A. Y., Jansen, R. K. & Ashworth, M. A., 2018, Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta), Phytotaxa 347 (1), pp. 1-49 : 46-47

Key to “big stick” araphids in this paper (excluding Pteroncola ). Requires both LM and SEM observations.

1. Valves with biseriate striae (sternum often visible in LM, virgae may be visible, but striae pores not), ocellulimbus (sunken apical pore field) present (visible only in SEM)...........................................................................................................................................2

- Valve with line of single areolae, often sunken and crossed by a bar, along each margin of the valve (visible in LM); rimoportula covers symmetrical; ocellulimbus absent.............................................................................................................. Thalassionema ; 17

2. Virgae> 37 in 10 μm, biseriate, comprised of densely spaced rows of small pores; apical spine(s) usually present; ocellulimbus usually moderate to very deeply sunken; rimoportula covers symmetrical or asymmetrical; apical spines present.........................3

- Striae 18-37 in 10 μm, comprised of large areolae arranged partially or entirely in decussate pattern (usually only visible in the SEM); ocellulimbus shallowly sunken, 3 pores deep; rimoportula covers asymmetrical; apical spines absent; [valves of species described here are often curved, but this may not be so in other species] ..................................................................... Divergita ; 15

3. Rimoportula covers symmetrical; ocellulimbus very deeply sunken, 3–4 to 7–10 pores deep Stricosus .......................................... 9

- Rimoportula covers asymmetrical; ocellulimbus shallow to deeply sunken, exactly 3 pores deep Hyalosynedra ...........................4

4. Cells linear, very long,> 80 μm and often 200–300 μm long; 4–5 spines ...................................................................... H. laevigata

- Cells <100 μm long; (0?)–1–4 spines................................................................................................................................................5

5. Apices capitate or subcapitate............................................................................................................................................................6

- Apices rounded...................................................................................................................................................................................7

6. Sternum linear, narrow; striae 56–60 in 10 μm; ocellulimbus 12–14 pores wide............................................................... H. hyalina

- Sternum lanceolate, narrow; striae 50–54 in 10 μm; ocellulimbus 6–8 pores wide .................................................. H. sublaevigata

7. Sternum linear, medium width; small cells, length 13–33 μm..................................................................................... H. al-shareefii

- Sternum lanceolate and narrow; cells 30–109 μm long.....................................................................................................................8

8. Cells 30–48 μm long, 2.6–3.5 μm wide; ocellulimbus 6–8 pores wide............................................................................. H. al-turkii

- Cells 43–109 μm long, 3.6–6.9 μm wide; ocellulimbus 10–14 pores wide...................................................................... H. prasadii

9. Rimoportula slit S-shaped; sternum linear, medium width .................................................................................................. S. madani

- Rimoportula slit straight; sternum linear or lanceolate....................................................................................................................10

10. Sternum linear, narrow.....................................................................................................................................................................11

- Sternum lanceolate, narrow or medium width.................................................................................................................................13

11. Cells almost linear, 88–152 μm long, and relatively broad; one spine over the ocellulimbus;........................................ S. harrisonii

- Cells narrowly lanceolate; two spines over the ocellulimbus;.........................................................................................................12

12. End converging to round; valves 46–186 μm long .......................................................................................................... S. alfageehii

- End parallel to weakly capitate; valves 114–232 μm long............................................................................................... S. cardinalii

13. Valves <152 μm long.................................................................................................................................................. S. navarroensis

- Valves> 153 μm long.......................................................................................................................................................................14

14. Valves 153–358 μm long; virgae 44–52 in 10 μm; 4–7 spines ........................................................................................... S. gracilis

- Valves 288–397 μm long; virgae 37–41 in 10 μm; 2–4 spines ...................................................................................... S. blumbergii

15. Valve extremely long and narrow, 136–297 μm long, 2.9–4.2 μm wide; 18–33 virgae in 10 μm; ocellulimbus 16–24 pores wide... ......................................................................................................................................................................................... D. capillaris

- Valves lanceolate; morphometrics not as above...............................................................................................................................16

16. Sternum lanceolate and narrow; cells 64–77 μm long, 4.3–5.6 wide; 29–37 striae in 10 μm; ocellulimbus 12–14 pores wide......... ....................................................................................................................................................................................... D. al-ghamdii

- Sternum lanceolate and broad; cells 174 μm long, 4.4 wide; 24–28 virgae in 10 μm; ocellulimbus 12–16 pores wide..................... ......................................................................................................................................................... D. toxoneides Edward C. Theriot

17. Very long cells, 383–403 μm long; areolae 9–10 in 10 μm ......................................................................................... T. cf. bacillare

- Cells shorter......................................................................................................................................................................................18

18. Cells 77–84 μm long; areolae 5–6 in 10 μm ............................................................................................................ T. cf. frauenfeldii

- Cells 51–61 μm long; areolae 8–9 in 10 μm .......................................................................................................... T. cf. nitzschioides