Psammodiscus nitidus (Gregory) Round & D.G. Mann (1980: 371)

Watanabe, Tsuyoshi, Nagumo, Tamotsu, Sun, Zhongmin, Hasegawa, Kazukiyo, Miyagawa, Tomofumi, Kumada, Misato & Tanaka, Jiro, 2013, Morphology and taxonomy of Psammodiscus Round & Mann (Bacillariophyceae: Rhaphoneidales) with a description of the new species Psammodiscus calceatus, Phytotaxa 124 (1), pp. 1-12 : 2

Psammodiscus nitidus (Gregory) Round & D.G. Mann (1980: 371) ( Figs 1–18 )

Basionym: Coscinodiscus nitidus Gregory (1857: 499 , pl. 10, fig. 45)

TYPE:— UK: Scotland, Lamlash Bay ( BM 1343 , Hendey 1964: 76, syntype) .

Size and shape: Cells solitary, attached to sand grains ( Figs 1a, b ). Valves circular to slightly elliptic in valve view ( Figs 2–4 ). Valve diameter 13.5–28.5 µm, 8–9 striae in 10 µm, 8 areolae in 10 µm ( Table 1).

Plastids and nucleus: Discoid plastids located along valve surface, number ca. 90 ( Fig. 5 ). Nucleus lies at cell centre ( Fig.5 ).

Fine structures of valve: Valve face flat ( Fig. 6 ), striae radiate, reaching mantle ( Fig. 6 ). Areola on valve face ( Figs 7, 8 ) and mantle ( Fig. 8 ) occluded by rotae with 2–3 spokes. Internal views of small valves not observed. Larger valves ( Figs 9 and 12 ) originate from same frustule. Striae and areolae of large valves morphologically similar to those in smaller valves ( Figs 9–11 ); occasionally areola abnormalities visible ( Fig. 10 ). Spokes in areolae not observed from internal view ( Fig. 14 ).

Rimoportula: Number of rimoportulae 0–2 ( Figs 6, 12, 15 ) per valve. Rimoportula external opening located near valve centre ( Figs 6, 7 ). Some valves lack central rimoportula ( Fig. 15 ). In larger valves, external opening of rimoportula observed near valve margin ( Fig. 10 ). In internal view, two rimoportulae located at opposite sides near valve margin ( Figs 12–14 ). Rimoportula sessile with simple slit surrounded by ridge ( Figs 13, 14 ).

Central small pore: Central small pore located near valve centre ( Figs 6, 7 ).

Additional small pore: In larger valve, external opening of small pore observed near valve margin ( Fig. 10 ). Additional small pore situated close to rimoportula near margin ( Fig. 14 ).

Cingulum: epicingulum consisting of three open bands: valvocopula ( VC), second (2B) and third (3B) bands ( Figs 17a, b ). Valvocopula and second girdle bands open at 180° to each other ( Figs 15, 16, 18 ). VC with two rows of pores ( Fig. 16 ), its opening covered by ligula of 2B ( Figs 16, 17a, 17b ). 2B with single row of pores ( Fig. 17a, b ). 3B narrow with single row of triangular non-occluded pores ( Figs 17a, b ).

Figures

FIGURES 5. Psammodiscus nitidus (CLSM). Each row (A, B, C) taken at valve surface, shallow and deep focuses, respectively. Note numerous discoid plastids. Column I, DIC; Column II, autofluorescence of plastids; Column III, DAPI stained nucleic acid. P = plastid; N = nucleus. Scale bar = 10 µm.

FIGURES 1–4. Psammodiscus nitidus (LM). Figs 1a, b: Solitary cells attached to sand grains, living cells from TW153 (BF), solitary attached cells (two circles in fig. 1b) to a sand grain (figs 2a and b are the same image at different focal depths). Figs 2–4. Valves (BF): Fig. 2 from TW166, figs 3 and 4 from TW159. Scale bars = 50 µm (Fig. 2), 10 µm (Figs 3–5).

FIGURES 6–18. Psammodiscus nitidus (SEM). Fig. 6. Complete frustule, view of hypovalve (HV), square is enlarged view in fig. 7. Fig. 7. Valve face, external openings of rimoportula (Ri) and small pore (SP), note small pore located near valve centre. Fig. 8. Mantle, areolae (A) occluded by plated rotae (R) with 2–3 spokes (S). Fig. 9. External view of large valve, note valves in figs 9 and 12 generated from the same cell; rectangle (a) is enlarged view in fig. 10; rectangle (b) is enlarged view in fig. 11. Fig. 10. External openings of small pore (SP) and rimoportula (Ri). Fig. 11. External view of fractured valve; areolae (A) occluded by plated rotae (R) with 3 spokes (S). Fig. 12. Internal view of large valve, rectangle (a) is enlarged view in fig. 13; rectangle (b) is enlarged view in fig. 14. Fig. 13. First rimoportula (Ri1), note rimoportula located near margin. Fig. 14. Second rimoportula (Ri2) and small pore (SP), note both rimoportula and small pore are located near the margin. Fig. 15. Complete frustule, note small pore (SP) located near centre of hypovalve (HV); no rimoportula; square (a) is enlarged view in fig 16; square (b) is enlarged view in fig 18. Fig. 16. Valvocopula (VC) opening (OVC) occluded by ligula (L2B) of second band (2B); epivalve (EV). Fig. 17a. Opposite view from fig. 16; hypovalve (HV), valvocopula (VC) opening (OVC), ligula (L2B) of second band (2B), third band (3B). Fig.17b. Schematic drawing of fig. 17a; Pores (P), note pores of second band are circular holes, pores of third band are triangle. Fig. 18. Second band (2B) opening (O2B); valvocopula (VC) and third band (3B). Note third band either in formation or is eroded. Scale bars = 10 µm (Figs 9, 12, 15), 5 µm (Fig. 6), 1 µm (Figs 7, 8, 10, 11, 16– 18), 0.5 µm (Figs 13, 14).