Gomphonema angusticephalum Reichard & Lange-Bertalot

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 : 257

Gomphonema angusticephalum Reichard & Lange-Bertalot ( Figures 119–166 , 268–274 )

Length: 15.3–33.3 μm, breadth: 4.7–6 μm, striae: 11–14 in 10 μm. It is possible to divide individuals found in Lake Baikal into two groups ( Figs 119–141 and Figs 142–166 , respectively) on the basis of breadth and valve undulations. Valves shown by us in Figs 119–141 conform with the type population shown by Reichardt (1999, pl. 60, figs 1– 12), whereas valves shown in Figs 142–166 are more slender and present distinctly narrower footpoles. It seems doubtful that the populations shown by Reichardt (1999) in his figures 13–20, 21–26, 27–29 and 30–34 belong to G. angusticephalum . SEM: images of the valve exterior of G. angusticephalum are shown in Figs 268–274 . Valves have large, distinct C - shaped areolae. The center of the valve has proximal raphe ends that are dilated and straight to barely deflected towards the round stigma opening ( Figs 268, 269, 271, 273 ). The distal raphe end is strongly deflected onto the mantle at the headpole ( Figs 270, 272 ).At the footpole, porelli appear restricted to the valve mantle and are bisected by the hooked distal raphe end ( Fig. 274 ).

Figures

FIGURES 119–166. LM. 119–166. Gomphonema angusticephalum. Scale bar = 10 μm.

FIGURES 268–273. Gomphonema angusticephalum, external views. 268, 271. General valve views. 269, 273. Central area with dilated proximal raphe ends and small, round stigma opening evident. 270, 272. Headpole, with distal raphe ends hooked onto valve mantle. Areolae appear C-shaped. Sclae bars = 5 μm in Figs 268, 271; 1 μm in Figs 269, 270, 272, 273.

FIGURES 274–279. SEM. 274. Gomphonema angusticephalum. External view of footpole, showing deflected distal raphe end bisecting bilobed pore field. Porelli are differentiated from C-shaped areolae. 275–279. Gomphonema laticollum. 275–278. External viws. 279. Internal view. 275, 276. Whole valve views showing outline of the valves. 277. Central area with undulate raphe dilated proximal raphe ends and round stigma opening evident. C-shaped areolae dominate the valve. 278. Headpole showing C-shaped areolae and hooked distal raphe end. 279. Valve view with central nodule, helictoglosae and note presence of pseudosepta. Scale bars = 1 μm in Fig. 274, 2 μm in Figs 277, 278; 5 μm in Figs 275, 276, 279.