Gomphonema pseudacuminatum Kulikovskiy, Kociolek & Solak, 2015

Kulikovskiy, Maxim S., Kociolek, John P., Solak, Cüneyt N. & Kuznetsova, Irina, 2015, The diatom genus Gomphonema Ehrenberg in Lake Baikal. II. Revision of taxa from Gomphonema acuminatum and Gomphonema truncatum-capitatum complexes, Phytotaxa 233 (3), pp. 251-272 : 254-256

Gomphonema pseudacuminatum Kulikovskiy, Kociolek & Solak , sp. nov. ( Figs 46–75 , 260–267 )

Valves heteropolar, clavate, gibbous and biconstricted. Headpole cuneate, often with a very slightly pronounced apiculus; basal part is elongate - cuneate, gradually narrowing to the footpole, usually with almost straight margins. Apical inflation is consistently wider than the middle one. Marginal undulations distinct. Length: 22.7–48.0 μm, breadth: 6–8 μm. Striae punctate, uniseriate along the entire length, parallel to slightly radiate in center, more strongly radiate at the footpole, 10–12 in 10 μm. Axial area distinct, narrow. Central area small, a few striae in central part are shorter. Stigma isolated and distinct. Bilobed apical pore field resolved at the footpole. SEM: Valve exterior with distinct C - shaped areolae ( Figs 260–267 ). Distal raphe ends are broadly deflected onto the mantle at both poles ( Figs 260 , 263–264, 266, 267 ). The apical pore field has some porelli on the valve face, but most are on the valve mantle ( Figs 263, 264, 266 ). Proximal raphe ends dilated and bent slightly towards the round stigma opening ( Figs 261 , 264, 265 ).

Type: — RUSSIA. Lake Baikal: shallow bay from south part of Lake Baikal at 8 km from Enkhaluk village, 52º 27.042’ N, 106º 53.215’ E, M. Kulikovskiy, 14 July 2011 (holotype: IBIW! slide no. 18609 = Fig. 48 ).

Etymology: —Epithet refers to similarity of this taxon with G. acuminatum .

Observations: —This taxon differs from G. acuminatum by having narrower valves, more narrow apical inflations and more cuneate apical ends without a strongly differentiated apiculus. Metzeltin et al. (2009: pl. 165, figs 4–10) recognized the same taxon from Mongolia and considered it under name “ Gomphonema spec. cf. interpositum Reichardt ”, however, G. pseudacuminatum sp. nov. is distinguished from G. interpositum Reichardt (1999: 47) by the shape of the valves. It is possible that G. pseudacuminatum sp. nov. is a widespread taxon, but its distribution may be masked by it being recognized previously as G. acuminatum .

Figures

FIGURES 46–87. LM. 46–75. Gomphonema pseudacuminatum sp. nov. Fig. 48 is of the holotype. 76–87. Gomphonema sp. Scale bar = 10 μm.

FIGURES 256–261. SEM.256–261. Gomphonema acuminatum. External views. 256. External view of central area to headpole.Proximal and distal ends evident. 266. Central area with dilated proximal raphe ends and small, round stigma opening evident. 258. Headpole showing protracted apex and hooked distal raphe end. 259. Footpole with deflected distal raphe end bisecting apical pore field on the valve mantle. 260, 261. Gomphonema pseudacuminatum sp. nov., external views. 260. Entire valve view showing valve proportions. 261. Central area with dilated proximal raphe ends, small elliptical stigma opening and occlusion of areolae resulting in C-shaped openings. Scale bars = 5 μm in Figs 256, 260, 2 μm in Fig. 258, 1 μm in Figs 257, 259, 261.

FIGURES 262–267. SEM. 262–267. Gomphonema pseudacuminatum sp. nov., external views. 262, 267. Headpole with distal raph branch deflected onto mantle. 263, 266. Footpole with apical pore fields almost entirely on mantle. Porelli of the bilobed pore field are differentiated from C-shaped areolae. 264. General valve view showing outline of valve. 265. Central area. Proximal raphe ends are straight and stigma opening is small, elliptical. Areolae are C-shaped. Scale bars = 5 μm in Fig. 264, 1 μm for Figs 262, 263, 265–267.