Gomphonema cf. truncatum Ehrenberg, 1832

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 : 260

Gomphonema cf. truncatum Ehrenberg ( Figs 191–213 , 289–293 )

Valves clavate, swollen at the center of the valve. Length: 20–36 μm, breadth: 9.3–11.3 μm. Headpole is broadly rounded, capitate and footpole is narrow. Axial area is narrow. Central area small, rectangular. A stigma is present in the central area close to the proximal raphe endings. Striae punctate, distinctly radiate, 10–14 in 10 μm. SEM: striae composed of biseriate or biseriate turning to uniseriate striae, the areolae with volate occlusions giving the areolae C - or S - shaped openings. Areolae bordering the axial area C-shaped, with the closed side of the C facing the axial area. Raphe undulate, with proximal ends dilated. Stigmal opening small, round ( Figs 289–290 ). Distal raphe end deflected onto the mantle ( Figs 291–293 ). Apical pore fields with a few porelli on the valve face, extending onto the mantle. Pore fields are bisected by the distal raphe end. Porelli are physically and structural differentiated from the areolae ( Fig. 292 ).

Observations: —The population considered here appears to be closely related to G. truncatum Ehrenberg sensu Reichardt (2001) by having biseriate striae evident in SEM. They differ, however, by the population from Lake Baikal having smaller and more elongate valves.

Figures

FIGURES 187–227. LM. 191–213. Gomphonema cf. truncatum. 214–227. Gomphonema paracapitatum sp. nov. Fig. 214 is of the holotype. Scale bar = 10 μm.

FIGURES 286–291. SEM. 286–288. Gomphonema microlaticollum sp. nov. Internal views. 286.Whole valve view showing outline. 287. Headpole with helictoglossa and narrow pseudoseptum present. 288. Footpole showing offset helictoglossa and pseudoseptum. 289–291. Gomphonema cf. truncatum, external views. 289. Whole valve view. 290. Central area. Biseriate striae become uniseriate near the axial area. Areolae are C-shaped. Dilated proximal raphe ends and small, round stigma opening are evident. Raphe is undulate. 291. Headpole with striae and deflected distal raphe end evident. Scale bars = 5 μm in Figs 286, 289; 1 μm in Fig. 287; 0.5 μm in Fig. 288; 2 μm in Figs 290, 291.

FIGURES 292–297. SEM. 292. Gomphonema cf. truncatum. External views. Footpole, with deflected distal raphe end and apical pore field mostly on the valve mantle. Porelli are physically separated from and morphologically differentiated from C-shape areolae. 293. Valve view with undulate raphe and C-shaped areolae distinct. 294. Gomphonema paracapitatum sp. nov., external view. Girdle view showing wedge-shaped frustule and extension of striae from valve view onto mantle. 295–297. Gomphonema capitatum, external views. 295. General valve view. 296. Central area with distinct C-shaped areolae. Proximal raphe ends are dilated weakly. 297. Headpole, Cshaped areolae evident. Scale bars = 1 μm in Fig. 292; 5 μm in Figs 293, 294; 10 μm in Fig. 295; 2 μm in Figs 296, 297.