Gomphonema densistriatum Levkov, 2011

Levkov, Zlatko & Williams, David M., 2011, Fifteen new diatom (Bacillariophyta) species from Lake Ohrid, Macedonia, Phytotaxa 30, pp. 1-41 : 30-31

Gomphonema densistriatum Levkov , sp. nov. ( Figs 210–221 , 253–258 )

Valvae lineari–lanceolatae vel anguste clavatae verticibus late rotundatis polis basalibus angustius rotundatis vel subprotractis. Longitudo valvae 34–44 µm, latitudo valvae 7.2–8.5 µm. Raphe filiformis poris centralibus distinctis. Area axialis angusta linearis, area centralis variabiliter dilatata ad instar rhombica vel transverse elliptica. Stigma solitaria abest. Striae transapicales valde radiate in media parte, leviter radiate vel parallelae sub apices, 15–18 in 10 µm.

Type:— MACEDONIA. Lake Ohrid, Bay of St. Naum rock scrape, shore, collection date: 17 March 2007 (accession No. MKNDC 001122). Slide BM 101480 (holotype). Slide MKNDC 001122 (isotype) .

Valves linear-lanceolate to narrowly-clavate, with broadly rounded head poles, narrowly rounded to subprotracted foot poles. Valve length 34–44 µm, valve width 7.2–8.5 µm. Raphe filiform with distinct central pores. Axial area narrow, linear. Central area variable in shape and size, broadly elliptical to rhombic. Striae strongly radiate in valve middle, becoming slightly radiate to parallel near apices, 15–18 in 10 µm. (LM).

Valve face flat, transition to valve mantle gradual ( Figs 253–255 ). Raphe centrally located ( Figs 253, 255 ). Proximal raphe endings widened into teardrop-shaped central pores ( Fig. 254 ). Distal raphe endings at head pole continuing as slightly curved terminal fissures passing on valve mantle ( Fig. 255 ). Striae biseriate, composed of small round areolae. Apical pore field present on base pole, bisected by distal raphe endings ( Fig. 256 ). Several isolated pores at central area, without stigmata ( Figs 254, 255 ). Internally ( Figs 257, 258 ), proximal raphe endings unilaterally hooked ( Fig. 258 ). Distally, raphe terminates with prominent helictoglossae ( Fig. 257 ). Stigmata are absent in the central area ( SEM).

Observations:—The main differential characters of G. densistriatum are the valve shape (linear– lanceolate) and the high striae density. Comparable striae density is found in the valves of G. perolivaceoides (S= 12–17 µm) but the latter has broader (B= 9.5–11 µm) and more broadly clavate valves. G. olivaceolacuum can be differentiated by valve shape (broadly clavate) and the shape of the head pole (obtusely rounded to truncate).

Figures

FIGURES 210–240: LM micrographs. Figs 210–221. Gomphonema densistriatum. Figs 222–230. Gomphonema subolivaceum. Figs 230–240. Gomphonema fonticolum. Scale bar = 10 µm.

FIGURES 253–258: SEM micrographs of Gomphonema densistriatum. Figs 253, 255. External view of whole valves. Fig. 254. Detail of mid-valve showing small central area, teardrop-shaped central pores and biseriate striae. Fig. 256. Detail of base pole showing distinct APF and straight distal raphe fissure. Fig. 257. Internal valve view. Fig. 258. Detail of mid–valve. Scale bars in Figs 253, 255, 257 = 10 µm; Figs 254, 256, 258 = 5 µm.