Gomphoneis perolivaceoides (Levkov) Kociolek & Kulikovskiy, 2013

Kociolek, John P., Kulikovskiy, Maxim S. & Solak, Cüneyt N., 2013, The diatom genus Gomphoneis Cleve (Bacillariophyceae) from Lake Baikal, Russia, Phytotaxa 154 (1), pp. 1-37 : 24

Gomphoneis perolivaceoides (Levkov) Kociolek & Kulikovskiy comb. nov.

Basionym: Gomphonema perolivaceoides Levkov in Levkov, Krstic, Metzeltin, & Nakov 2007: 65, pl. 177, figs 1–21.

In addition to recognizing two groups within the Elegans lineage of Gomphoneis , namely those with 4 (or more) stigmoids and those where stigmoids or stigma is wanting, we can also observe features shared across the two groups. In every one of the Gomphoneis species we observed in Lake Baikal, features shared include doubly-punctate striae, apical pore fields at the footpole that are undifferentiated, presence of septa and pseudosepta, and a central nodule bearing proximal raphe ends recurved in the same direction.

There were several taxa and features that were variable across members of the genus. For example G. lata has robust interstriae and in some specimens or on certain portions of the valve (apices), striae were composed of both 2 and 3 rows of areolae. Gomphoneis lata and G. tumida (see figures 383–387) both exhibited stigmoids with teeth-like projections internally, and that feature is also present in G. marvanii ( Reichardt 2009, figure 82).

Gomphoneis hastata and its allies, as well as G. eriensioides (figures 398, 401), have external stigma openings that occur in small depressions on the valve face. Internally, the stigmoids are occluded, and there are small openings around the stigma. Also, relative to the stigmoids, G. capitata showed 4 isolated stigmoids externally, but only two stigma openings internally ( Figs 392–395 ). Internal stigma openings are not occluded in G. capitata sp. nov., and this feature is also seen in G. inconspicua sp. nov. ( Fig. 409), G. skabitchevskii sp. nov. (Fig. 410) and G. cf. subcapitata (Fig. 406).

Position of the apical pore field in most Gomphoneis taxa is both on the valve face and valve mantle. This is known in both major groups within the genus, and across many taxa in the Elegans subgroup ( Kociolek & Stoermer 1986, 1988b; Levkov et al. 2007; Tuji 2005; You et al. 2013). There were two taxa in Lake Baikal, however, where the apical pore fields were structured differently. In G.potapovae sp. nov. ( Figs 417, 418 ), and G. strelinkovae sp. nov. ( Fig. 412, 413 ), the apical pore field does not extend onto the valve face, but rather is restricted to the valve mantle; this is also seen in G. sp. cf. reichardtii ( Fig. 421 ).

This variation in the valve structure in stigmoid or astigmoid groups of Gomphoneis has not been recognized previously. Further assessment of these features in recently described, or historically known taxa, may help to further resolve evolutionary relationships of the Gomphoneis taxa within and outside of Lake Baikal. Such a detailed understanding of the relationships of these taxa may yield an understanding of the distributions across the lake and the arc eastward from the Balkans to eastern Asia through NW China, Mongolia, Lake Baikal and the Russian Far East to Japan, and westward from North America.

Figures

PLATE 14: SEM. Gomphoneis metzeltinii. Figs 389–391: Extenal valve views. Figs 389, 390: Whole valve views should fine striae and indistinct stigmoids. Proximal raphe ends are dilated slightly. Fig. 391. Footpole shows the rounded porelli of the apical pore field appear as condensed striae. G. capitata. Figs 392–396: Figs 392–395: Internal valve views. Figs 392–394: Entire valve views. Fig. 392: Specimen with girdle bands shows septa at the poles, wide, rectangular central area and central nodule with recurved proximal raphe ends. Fig. 393: Specimen lacking girdle bands revealing the smaller pseudosepta at the poles. The helictoglossae are evident also. Only two stigmoid openings are evident around the central nodule. Fig. 394: Specimen without girdle bands, showing pseudosepta, recurved proximal raphe ends on small central nodule, and helictoglossae at the poles. Fig. 395: Internal valve view showing only two prominent stigmoidal opening. The appear simple, without occlusions. Fig. 396: External valve view. The valve has proximal raphe ends that are prominently dilated, and has 2 types of stigmoidal openings, one larger and one smaller.

PLATE 17: SEM. Gomphoneis strelnikovae. Figs 412–416: Figs 412, 413: External valve views showing the raph brach with dilated proximal raphe ends. Even though the striae around the central area terminate with a single areolae, there are not stigmoids internally. The apical pore field is positioned entirely on the valve mantle, porelli do not extend onto the valve face. Figs 414–416: Internal views. The central nodule is not well distinguished from the rest of the central area, and bears the proximal raphe ends that recurved in the same direction. Helictoglossae and pseudosepta are present at the poles. G. potapovae. Figs 417–419: Figs 417–418: External valve views showing straight raphe with slightly dilated proximal ends. The doubly punctate striae end in single areolae; those around the central area appear larger than others. Porelli are located on the valve mantle. Fig. 4192: Internal valve view with septa evident at the poles, along with helictoglossae. The central nodule is raised internally, and bears the proximal raphe ends recurved in the same direction. G. sp. cf. reichardtii. Figs 420–421: Fig. 420: Internal valve view with 4 isolated stigmoids evident. Their openings are simple. The central nodule is small, and bears recurved proximal raphe ends. The poles have helictoglossae and pseudosepta. Fig. 421: External view showing the apical pore field restricted to the valve mantle. The raphe is slightly undulate, and the proximal raphe ends are dilated.