Gomphonema mihoi Levkov, 2011

Levkov, Zlatko & Williams, David M., 2011, Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia, Phytotaxa 30, pp. 1-41 : 23-25

Gomphonema mihoi Levkov , sp. nov. ( Figs 140–148 , 172–177 )

Valvae distinctius lineari–clavatae verticibus distincte obtusius rotundatis quam basipoli. Longitudo valvae 18–37 µm, latitudo valvae 4.5–6.2 µm. Raphe filiformis poris centralibus distinctis. Area axialis angusta linearis, area centralis lata , rectangularis. Stigma solitaria propius ad centrum noduli centralis sita. Striae transapicales radiate vel parallelae sub apices, indistincte punctatae 14–17 in 10 µm.

Type:— MACEDONIA. Lake Ohrid, Bay of Ljubanishta , Chara squeeze from depth 6–7 m; collection date: 2 April 2007 (accession No. MKNDC 001203 ). Slide BM 101476 (holotype). Slide MKNDC 1203 .

Valves distinctly club-shaped, narrowly linear, head poles more obtusely rounded than foot poles. Valve length 18–37 µm, valve width 4.5–6.2 µm. Raphe filiform with distinct central pores. Axial area narrow, linear. Central area broad rectangular. Single isolated stigma present in central area, positioned close to the central pores. Striae slightly radiate to parallel near apices, finely punctate, 14–17 in 10 µm (LM).

Frustules wedge-shaped in girdle view ( Fig. 172 ). Girdle bands with single row of small round poroids. Striae not interrupted on valve mantle, having typical C-like external areolae openings. Valve face smooth ( Figs 173, 174 ). Apical pore field present at base pole, bisected by doubly curved distal raphe ending ( Fig. 176 ). Pore field composed of round porelli arranged in oblique rows. Raphe located in middle of valve; raphe branches straight to weakly undulate. Central pores slightly widened and unilaterally deflected towards the stigma; central area wide ( Fig. 174 ). Single central stria shortened on both valve sides. Striae uniseriate, composed of relatively large, elliptical to oval areolae. Areolae with reniform vela. Internally ( Figs 175, 177 ), pseudoseptum present on the poles. Internal opening of stigma round, with reniform velum similar to areolae. Distal raphe endings terminate with helictoglossae. Proximal raphe endings recurved on elevated central nodule and widened at end ( SEM).

Observations:—There are several small-celled species present in Lake Ohrid. Gomphonema balcanicum Levkov & Krstic (in Levkov et al. 2007: figs 169: 11–23, figs 170: 1–8) can be easily differentiated by its very narrow central area and the shape of its foramina. Gomphonema sancti-naumii Metzeltin & Levkov (in Levkov et al. 2007: figs 171: 1–15) has biseriate striae composed of small round areolae. Gomphonema pseudotenellum Lange-Bertalot (in Krammer & Lange-Bertalot 1985: figs 35: 7–12) has narrower valves (B= 3–4 µm) with cuneate apices. Gomphonema mihoi might also be confused with several other species so far not recorded from Lake Ohrid. Gomphonema bohemicum Reichelt & Fricke (in Schmidt 1874 –1959: figs 235: 18–25) has a wide unilateral central area which extends to the valve margin ( Reichardt 1999: figs 61: 1–22). Gomphonema angustatum (Kützing) Rabenhorst (1864: 283) has lanceolate to rhombic–lanceolate valves with acutely rounded to cuneate ends; compared to G. mihoi , it has more distantly spaced striae (10–14 in 10 µm) composed of densely positioned small C-like areolae ( Reichardt 1999: figs 23: 1–10, 13–16, figs 24: 1– 37). The valve mantle of Gomphonema clavatulum Reichardt (1999 : figs 25: 1–23, 27, 28) has 2–3 rows of relatively coarse punctae in contrast to the single row of areolae present in G. mihoi . The central area in G. clavatulum is narrow, made by a slight shortening of central striae and can hardly be differentiated from the axial area (opposite to broad, clearly differentiated central area). Similarly, the differences between G. mihoi and G. paludosum Reichardt (1999 : figs 26: 1–22, figs 27: 1–9) are the shape of the central area, areolae morphology and striae density (9–14, usually 10–12 in 10 µm).

Species with similar shaped valves to G. mihoi are from the G. pumilum Reichardt & Lange-Bertalot complex ( Reichardt 1997). In general, differences are found in the striae density. The interstriae of the valves in the G. pumilum complex are wide (even wider than the striae) in contrast to the very narrow interstriae in G. mihoi . Additionally, differences in areolae morphology can be found. The areolae in G. pumilum are occluded with a single reniform vola giving the impression of C-shaped foramina. The external opening of the stigma in G. pumilum is surrounded by a rim, while internally the stigma has a simple opening (compare Figs 172–174 with Reichardt 1997: figs 1: 1–7).

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 172–177: SEM micrographs of Gomphonema mihoi. Fig. 172. Frustule in girdle view. Fig. 173. External view of whole valve. Fig. 174. Detail of central area, showing proximal raphe endings, stigma and areolae. Fig. 175. Internal view of whole valve. Fig. 176. Detail of base pole showing APF and distal raphe fissures. Fig. 177. Internal valve view, detail of central area, showing internal openings of areolae and stigma. Scale bars in Fig. 172 = 10 µm; Figs 173, 175 = 5 µm; Figs 174, 176, 177 = 2 µm.