Halamphora submontana (Hustedt) Levkov, 2009

You, Qingmin, Kociolek, John Patrick & Wang, Quanxi, 2015, Taxonomic studies of the diatom genus Halamphora (Bacillariophyceae) from the mountainous regions of southwest China, including the description of two new species, Phytotaxa 205 (2), pp. 75-89 : 82

Halamphora submontana (Hustedt) Levkov ( Figs. 55–65 )

Description:— Valves semi-lanceolate, dorsiventral with smoothly convex dorsal margin and slightly convex ventral margin. Valve ends protracted, narrowly rounded and deflected ventrally. Length 18.3–21.8 μm, valve breadth 3.7–4.0 μm. Externally, the raphe is weakly arched and both proximal and distal raphe ends are deflected or curved towards the dorsal margin of the valve ( Figs. 60, 62, 64 ), proximal raphe ends almost not expanded ( Figs. 60, 62 ). Dorsal raphe ledge present. Axial area narrow. Dorsal striae more or less interrupted in the central area ( Figs. 60, 62 ). Dorsal striae beneath the raphe ledge are biseriate ( Fig. 62 ). Ventral portion of the valve with a semi-elliptical central area. Striae slightly radiate throughout, 32–38/ 10 μm, difficult to resolve with LM. Internally, the proximal raphe ends terminate at a narrow central helictoglossae ( Figs. 61, 63 ). Distally, internal raphe ends terminate as helictoglossae ( Fig. 65 ).

Distribution and ecology:— Weixi, Yunnan, China, altitude 1929 m a.s.l., collected in mountain river.

Observations:— This species has similar valve outline with Halamphora montana and the two are difficult to distinguish in LM. Differences between them are striae density ( H. submontana has more coarse striae, 32–38/ 10 μm, while H. montana has 45–50/ 10 μm) and striae structure ( H. submontana with biseriate striae near raphe ledge, H. montana without biseriate striae). The frustules of H. submontana and H. montana are very small, and with similar outlines, so they are confused with each other. In our study, in order to avoid wrong identification, we observed the specimen in SEM first ( Fig. 74 ), then examined same specimen in LM ( Fig. 70 ). This method facilitates correct identification with LM.

Figures

FIGURES 55–65. Halamphora submontana. 55–59. LM. Valve views showing size diminution series. Scale bars = 10 μm for all LM figures. 60–65. SEM. 60, 62, 64. External views. 60. Entire valve showing shape of the valve. 62. View of curved proximal raphe and biseriate dorsal striae beneath the raphe ledge. 64. View of curved distal raphe end. 61, 63, 65. Internal views. 61. Entire valve view. 63. Central area with a narrow central helictoglossae.65. View of valve end, with curved distal raphe ends and helictoglossa. Scale bars shown in each SEM figure.

FIGURES 66–77. Halamphora montana. 66–70. LM.Valve views showing size diminution series. Scale bars = 10 μm for all LM figures. 71–77. SEM. 71, 73, 74, 76. External views. 71, 74. Entire valve showing shape of the valve. 73. View of curved distal raphe end. 76. View of proximal raphe and larger areolae beneath the raphe ledge lie in a shallow depression. 72, 75, 77. Internal views. 72. Entire valve view. 75. View of valve end, with curved distal raphe ends and helictoglossa. 77. Central area with evident interrupted dorsal striae. Scale bars shown in each SEM figure.