Gomphonema linearoides Levkov, 2011

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

Gomphonema linearoides Levkov , sp. nov. ( Figs 199–209 , 246–250 )

Valvae distinctius lineari-clavatae verticibus distincte obtusius rotundatis quam basipoli. Longitudo valvae 24–35 µm, latitudo valvae 5.1–6.5 µm. Raphe filiformis poris centralibus distinctis. Area axialis angusta linearis, area centralis lata , rectangularis. Stigma solitaria abest. Striae transapicales valde radiate in media parte, leviter radiate vel parallelae sub apices, 7–11 in 10 µm.

Type:— MACEDONIA. Lake Ohrid, St. Naum springs, above ground springs, macrophytes, collection date : 25 April 2003 (accession No. MKNDC 000632 ). Slide BM 101479 (holotype). Slide MKNDC 000632 (isotype).

Valves distinctly club-shaped, narrowly linear, head poles more obtusely rounded than foot poles. Valve length 24–35 µm, valve width 5.1–6.5 µm. Raphe filiform with distinct central pores. Axial area narrow, linear. Central area broad panduriform. Striae strongly radiate in valve middle, becoming slightly radiate to parallel near apices, 7–10 in 11 µm (LM).

Raphe on post-initial cells not passing to valve mantle ( Fig. 246 ). Distal raphe endings at head pole are modified. Interstriae of vegetative cells broader than striae ( Figs 248, 249 ). Striae biseriate, composed of two rows of alternating, round areolae ( Figs 247, 248 ). Internally, proximal raphe endings unilaterally hooked ( Figs 249, 250 ) ( SEM).

Observations:—Two main characters are important for the differentiation of G. linearoides from other members of the G.olivaceum complex: its linear valves and low striae density. It can be distinguished from G. fonticolum ( Figs 231–240 , 251, 252 ) by the shape of the head pole (truncate in G. fonticolum ), shape of the base pole (subcapitate in G. fonticolum ) and striae density (9–14 in 10 µm in G. fonticolum ). Gomphonema olivaceum var. staurophora Pantocsek (1889: 56 , fig. 12: 206) has a low striae density (11.0– 12.5 in 10 µm) and similar valve outline but significantly differs with respect to the shape of the central area extending to the valve margins. Gomphonema olivaceum var. minutulum Mayer (1919: 207 , fig. 9: 26) has smaller, clavate valves (L= 15–20 µm) which makes differentiating the pair simple.

Figures

FIGURES 185–209: LM micrographs. Figs 185–198. Gomphonema perolivaceolacuum. Figs 199–209. Gomphonema linearoides. Scale bar = 10 µm.

FIGURES 246–252: SEM micrographs. Figs 246–250. Gomphonema linearoides. Fig. 246. External view of post-initial cell. Distal raphe endings modified and not passing on valve mantle. Mid-valve widened. Fig. 247. External view of whole valve. Fig. 248. Detail of mid-valve showing small central area, widened proximal raphe endings and biseriate striae composed of round to elliptical areolae. Fig. 249. Internal view of whole valve. Fig. 250. Detail of mid–valve, showing pinhole-shaped proximal raphe fissures and biseriate striae. Figs 251, 252. Gomphonema fonticolum. Fig. 251. External view of whole valve. Fig. 252. Internal valve view. Scale bars in Fig. 246 = 20 µm; Figs 247, 249, 251 = 10 µm; Figs 248, 250 = 2 µm, Fig. 252 = 5 µm.

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