Gomphonema dalatica Glushchenko, Kulikovskiy & Kociolek, 2017

Glushchenko, Anton, Kulikovskiy, Maxim & Kociolek, John Patrick, 2017, New diatom species from the Gomphonema subtile group in Southeast Asia, Phytotaxa 329 (3), pp. 223-232 : 227-229

Gomphonema dalatica Glushchenko, Kulikovskiy & Kociolek sp. nov. ( Figs 34–63 )

Description.

LM. Valves lanceolate-clavate with headpole protracted, capitate and footpole rounded. Length 40–64 μm, breadth 6.5–8.0 μm. Axial area narrowly lanceolate, forming a small, rectangular central area possessing a single, enlarged stigma positioned at the end of a central stria. Raphe more or less lateral, straight, with external proximal ends dilated slightly and distal ends deflected onto the valve mantle. Striae parallel to radiate, 12–15 in 10 μm, slightly coarser at the center of the valve.

SEM. The valve exterior has areolae occluded by flaps, giving the openings the appearance of being c-shaped ( Figs 56, 58, 60, 62 ). The center of the valve has dilated proximal raphe ends and enlarged, round stigmal opening ( Fig. 58 ). At the headpole, the distal raphe end is deflected onto the mantle ( Fig. 60 ). At the footpole, the apical pore field (APF) is positioned mostly on the valve mantle ( Fig. 62 ). Internally, there is a small central nodule, recurved proximal raphe ends, and a slit-like stigma opening ( Figs 57, 59 ). Helictoglossae are present, and small pseudosepta are evident at both apices ( Figs 61, 63 ). At the footpole, porelli of the APF are occluded.

Differential diagnosis. Differ from morphologically similar species G. pantropicum Reichardt by much finer stria density (12–15 in 10 μm, not 8–12 in 10 μm) and less radiate orientation of the striae.

Type: — VIETNAM. Lâm Đồng Province, Ðà Lạt Town, Đả Tiên Reservoir, N11°58.816’ E108°26.987’, E.S. Gusev & M.S. Kulikovskiy, 21 th June 2012, (collection of Maxim Kulikovskiy, I.D. Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences ( IBIW), holotype here designated, slide no 00269 = Fig. 39 ).

Etymology:— Epithet refers to the type locality.

Distribution. This species is known from the type locality and from Da Tanla Waterfall, waterbodies of Mỹ Sõn (Province Ninh Thuận), Ðà Lạt reservoir in Vietnam (as “ Gomphonema spec. ” Figs 117–120, Reichardt, 2015) and from Nam Leuk River in Laos (this investigation). Specimens of this species were found in samples 00269, 00984, 02269, 02406, 03817.

Figures

FIGURES 34–55: Gomphonema dalatica Glushchenko, Kulikovskiy & Kociolek sp. nov. LM. Size diminution series, valve views. Figure 39 is of the holotype. Scale bar = 10 μm.

FIGURES 56–63: Gomphonema dalatica Glushchenko, Kulikovskiy & Kociolek sp. nov. SEM. Figs 56, 58, 60, 62 are external views; 57, 59, 61, 63 are internal views. Fig. 56. Whole valve illustrating valve shape. Fig. 57. Whole valve, showing small pseudoseptum at each pole. Fig. 58. Valve center with slightly dilated proximal raphe ends, small, round stigma opening and areolae occluded by flaps that create C-shaped openings. Fig. 59. Valve center with small central nodule bearing recurved proximal raphe ends and slit-like stigmal opening. Striae are in troughs, with thickened rims around each areola. Fig. 60. Headpole, with the hooked-shaped distal raphe end curving onto the valve mantle. C-shaped areolar openings are evident. Fig. 61. Headpole, showing prominent helictoglossa and pseudoseptum. Fig. 62. Footpole, with round porelli positioned mostly on the valve mantle, physically separated, and morphologically distinct from the areolae. Fig. 63. Footpole, with large helictoglossa and pseudoseptum evident. Porelli are occluded internally. Small siliceous projections can be seen around the areolae. Scale bars = 5 μm (Figs 56, 57); 1 μm (Figs 58–60, 62); 0.5 μm (Figs 61, 63).