Gomphonema yaominae Gong & Li 2012, sp. nov.

Valvae lanceolate contractae gradatim medio apicibus angustatae abrupte e centro valvae versus basim-polum. Capitopolus rotundatus. Basi-polus anguste rotundatus. Longitudo 72–97 µm. Latitudo 13.0– 14.5 µm. Area axialis angusta ad apices, expansa dilute versus centrum, lanceolate. Area centralis indistincta facta stria mediana abbreviata. Raphe undulata distincte lateralis. Stigma distincte separatum stria approximatum nodulo centrali. Striae transapicales radiatae, 7–14/ 10 µm. Puncta 21–23/ 10 µm.

Valves lanceolate, gradually tapering towards headpole, more abruptly tapering from valve centre towards footpole. Headpole broadly rounded; footpole narrowly rounded. Valve length 72–97µm; breadth 13.0– 14.5µm. Axial area (sternum) narrow at apices, expanding slightly towards centre, lanceolate. Central area indistinct, formed by shortened median stria. Raphe undulate and distinctly lateral. Stigma distinctly separated from stria, close to central nodule. Striae slightly radiate, becoming radiate towards poles, 7–14 in 10µm. Puncta 21–23 in 10µm.

Type:— CHINA. Lake Shahu, Jiangxi Province, slide SH-01 (holotype illustrated in Figure 1, Museum of Nanjing Institute of Geography and Limnology, CAS, Nanjing, China).

Distribution and ecology:— Gomphonema yaominae has been found only in Lakes Shahu and Huangpi. Total phosphorus of the two lakes was 0.09 mg /L and 0.05 mg /L; total nitrogen was 0.78 mg /L and 0.34 mg / L; and both lakes were relatively base-high with conductivities between 89.50 and 192.00 µS/cm. Depths of Lakes Shahu and Huangpi were 1.33m and 1.09m; pH were 8.07 and 8.23; transparencies were 0.98 m and 1.01m, respectively (summarized in Table 1).

Eutrophication has occurred in most lakes of the middle and lower reaches of the Yangtze River and most species of diatom encountered were typical indicators of eutrophication (Yang et al. 2008). Further research in this area, especially in the typical habitats that species prefer, is necessary to gain a better understanding of their biogeography.

Observations:— In LM, the valves are lanceolate and gradually tapering towards headpole but more abruptly taper from the valve centre towards the footpole (Figs 1–6). The headpole is broadly rounded, while the footpole is narrowly rounded (Figs 1–6).

SEM observations of the valve exterior show the areolae with siliceous flaps, giving the openings a cshape near the axial area (sternum) and a long ‘strip shape’ at other parts of valve (Figs 7–10). The external proximal raphe endings are slightly expanded and rounded, slightly deflecting towards the primary side of the valve (Fig. 8). Distal raphe ends are deflected in the same direction onto the valve mantle (Figs 9, 10). At the footpole the distal raphe end bisects the porelli of the apical pore field. Porelli are physically separate and morphological differentiated from the valve face areolae (Fig. 10). The valve interior is dominated by the central nodule (Figs 11, 12). Proximal raphe fissures are unilaterally deflected and recurved towards the poles (Fig.12). Distal raphe fissures terminate as helictoglossae and are strongly deflected to the same side (Figs 13, 14). A small pseudoseptum is present at both the headpole (Fig. 13) and footpole (Fig. 14).

The specimens in the Lake Shahu material do not match data provided for previously described taxa. However, Gomphonema yaominae does share some features with several species in the genus, in particular G. affine Kützing (1844: 86) and G. affine var. rhombicum Reichardt (1999: 15). Gomphonema yaominae differs from G. affine var. rhombicum in the size of the valves and the density of its striae and puncta. The dimensions of G. affine var. rhombicum, as given by Reichardt (1999), are 35–62µm in length, 10–12.8µm in width, with 8–10 striae and 16–20 puncta in 10µm; these clearly differentiate it from those of G. yaominae which is larger in all dimensions (see above). The valve outline of G. yaominae is clavate, and only the smaller specimens resemble those of G. affine var. rhombicum.

The dimensions and morphology of G. affine Kützing are clearly different from those of G. yaominae: G. affine has valves with a similar shape to that of G. yaominae but in the latter the poles of the valve are obtusely rounded and the internal puncta near the mantle in SEM are is obviously larger (as seen in SEM).