Gomphosphenia tenuis Levkov & D.M.Williams, 2011

Levkov, Zlatko & Williams, David M., 2011, Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia, Phytotaxa 30, pp. 1-41 : 20-23

Gomphosphenia tenuis Levkov & D.M.Williams , sp. nov. ( Figs 131–139 , 161–171 )

Valvae distinctius lineari-clavatae verticibus distincte obtusius rotundatis quam basipoli. Longitudo valvae 22–42 µm, latitudo valvae 3.5–6.2 µm. Raphe filiformis poris centralibus distinctis. Area axialis variabilis, modice angusta quoad specimina minora sed lata quoad specimina maiora. Area centralis lata unilateraliter fasciam formans. Striae transapicales breves submarginales, radiantes to subparallelae 14–16 in 10 µm.

Type:— MACEDONIA. Lake Ohrid, Bay of St. Naum, rock scrape, small spring, collection date: 17 March 2007 (accession No. MKNDC 001124 ). Slide BM 101475 (holotype). Slide MKNDC 001124 (isotype) .

Valves distinctly club-shaped, narrowly linear, head poles more obtusely rounded than foot poles. Valve length 22–42 µm, valve width 3.5–6.2 µm. Raphe filiform with distinct central pores. Axial area variable, moderately narrow in smaller specimens, wide in larger specimens. Central area a broad unilateral fascia. Striae short, submarginal, radial to subparallel, 14–16 in 10 µm. (LM).

Valve face flat, transition of valve face to mantle forms a gentle right angle ( Fig. 161 ). Valve mantle fairly high, possessing single row of round to slit-like pores ( Fig. 161 ). Raphe branches straight, not passing onto valve mantle ( Figs 162, 163 ). Raphe proximally and distally expanded, terminating with tear-drop-shaped pores ( Figs 165, 166 ). Central pores slightly unilaterally deflected ( Fig. 164 ). Striae each composed of a single areola of variable shape; usually one central stria absent. Areolae near central area and apices have round foramina ( Figs 164, 165 ); remaining areolae are narrow slits positioned near valve margin. Apical pore field absent on both poles. Internally, pseudoseptum absent at both poles ( Figs 167, 169 ). Raphe branches straight, proximally terminate with anchor-shaped fissures ( Figs 168, 170 ), distally with small helictoglossae ( Fig. 171 ). Central nodule is elevated slightly from rest of valve ( Fig. 170 ). Internal openings of areolae much longer than external, occluded by hymenes ( SEM).

Observations:— Gomphosphenia tenuis belongs to subgenus Gomphosphenia ( Lange-Bertalot 1995) and is characterized by T-shaped internal central raphe endings and the absence of both a septum and pseudoseptum; the opposite is found in the subgenus Rhoicosphenula. Gomphosphenia tenuis closely resembles G. lingulatiformis (Lange-Bertalot & Reichardt) Lange-Bertalot (1993 : figs 83: 1–11; Lange- Bertalot 1995: figs 4: 1–4). Differences between the two concern the valve shape. The valves of G. lingulatiformis widen at the middle (the margin is undulated) and the valve apices are distinctly cuneate.

Gomphosphenia tenuis can easily be differentiated from G. grovei var. lingulata (Hustedt) Lange-Bertalot ( Hustedt 1927b: fig. 5:5, Simonsen 1987: figs 162: 1–7) by the valve shape and the shape of central and axial area. Gomphosphenia tackei (Hustedt) Lange-Bertalot ( Hustedt 1942: figs 16–18, Simonsen 1987: figs 459: 7–15) has a similar valve outline to G. tenuis but can be easily differentiated by the narrower valves (B= 2.5– 3.5 µm), finely punctate striae and very narrow central and axial areas. Gomphonema tackei var. brevistriatum Camburn (in Camburn et al. 1978: figs 14: 210–214) is even smaller (L= 12–16.5 µm; B= 2–3 µm) and the axial and central areas are indistinct.

Gomphosphenia reicheltii (M.Schmidt) Lange-Bertalot (1995) has distinctly punctate striae and lanceolate axial area in larger specimens and very narrow axial area in smaller specimens. There are probably two different species illustrated as Gomphonema reicheltii M. Schmidt in Schmidt (1899 in Schmidt 1874 – 1959: figs 214: 19–22); the valves depicted in figs 214: 19, 20 significantly differ in valve shape and shape of the central area from the valves illustrated in figs 214: 21, 22. However, detailed observation of type material is warranted for establishing the proper identity of both populations. Gomphosphenia oahuensis (Hustedt) Lange-Bertalot (in Moser et al. 1998) has isopolar valves with slightly protracted ends, in contrast to the narrowly-clavate valves in G. tenuis . Even larger differences can be observed with SEM in respect to raphe structure (compare with Moser 1998: figs 5: 6–8, figs 53: 1–9).

Gomphosphenia stoermeri Kociolek & E.W.Thomas (in Thomas et al. 2009) has smaller (L= 10–20.1 µm) and narrower (B= 1.5–3.1 µm) valves with a higher striae density (S= 28–35); the striae are composed of elongated areolae which extend to the raphe slits. These characters make differentiation between G.stoermeri and G. tenuis simple.

Gomphonema brasiliense Grunow (1878: 110) and Gomphonema demerarae (Grunow) Frenguelli (1941 : fig. 3: 11) should probably be transferred to Gomphosphenia ( Krammer & Lange-Bertalot 1985: figs 41: 1–5); both species significantly differ in the valve shape and size from G. tenuis .

Genus Gomphonema Agardh (1824)

Figures

FIGURES 131–160: LM micrographs. Figs 131–139. Gomphosphenia tenuis. Figs 140–148. Gomphonema mihoi. Figs 149–160. Gomphonema subaequale. Scale bar = 10 µm.

FIGURES 161–166: SEM micrographs of Gomphosphenia tenuis. Figs 161–163. External valve view; a single row of areolae present on valve mantle. Fig. 164. Detail of mid-valve, showing proximal raphe endings and striae composed of single areola. Proximal raphe endings widened and slightly deflected. One central striae/areola from one valve side absent. Fig. 165. Detail of head pole. Distal raphe fissure widened, terminates with teardrop-shaped pore. Fig. 166. Detail of foot pole. Raphe terminates with teardrop-shaped pore. APF not present on base pole. Scale bars in Fig. 161 = 5 µm; Figs 162, 163 = 10 µm; Figs 164, 166 = 2 µm; Fig. 165 = 1 µm.

FIGURES 167–171: SEM micrographs of Gomphosphenia tenuis. Figs 167, 169. Internal view of whole valves and girdle bands. Girdle band closed, bearing single row of round poroids. Internal foramina elongate and longer than external. On both ends, raphe terminates with small helictoglossae. Figs 168, 170. Detail of mid-valve showing slightly raised central nodule and anchor-shaped proximal raphe endings. Fig. 171. Detail of base pole. Typical APF not present at base pole. Areolae at pole have modified structure, having round foramina with cross-like occlusions. All other areolae entirely occluded. Scale bars in Figs 167, 169 = 5 µm; Figs 168, 170, 171 = 2 µm.