Assulina discoides, Bobrov & Shimano & Mazei, 2012

Bobrov, Anatoly, Shimano, Satoshi & Mazei, Yuri, 2012, Two New Species of Testate Amoebae from Mountain Forest Soils of Japan and Redescription of the Genus Deharvengia Bonnet, 1979, Acta Protozoologica 51 (1), pp. 55-63 : 61-62

Assulina discoides sp.nov. ( Figs 12–17 , Tables 2–3)

Description: Shell large in size, disc shaped ( Figs 13, 14, 16 ), colorless, transparent, narrow-elliptical in cross-section. The breadth of the shell usually exceeds the length ( Table 2). Aperture is narrow-elliptical with an uneven narrow organic lip ( Fig. 15 ). Aperture diameter is about 1/3 of the shell breadth. Surface is covered by large narrow elliptical idiosomes ( Figs 13–15 ) up to 10 µm in length and 5–6 µm in breadth.

The population is monomorphic. Variation coefficients of all the morphological characteristics are small ( Table 2).

List of associated testate amoebae. It was found in associations with the following species: Arcella arenaria Greeff, 1866 , A. arenaria compressa Chardez, 1974 , Centropyxis constricta (Ehrenberg, 1841) Deflandre, 1929 , C. sylvatica (Deflandre, 1929) Bonnet et Thomas, 1955 , Cyclopyxis eurystoma Deflandre, 1929 , Nebela tincta (Leidy, 1879) Awerintzew, 1906 , Phryganella acropodia (Hertwig et Lesser, 1874) Hopkinson, 1909 , Valkanovia elegans Schönborn, 1964 , Assulina discoides sp. n., A. muscorum Greef, 1888 , Euglypha compressa Carter, 1864 , E. compressa glabra Wailes, 1915 , E. laevis (Ehrenberg, 1832) Perty, 1849 , Deharvengia japonica sp. n., Corythion dubium Taránek, 1881 , C. dubium minima Chardez, 1969 , Trinema complanatum Penard, 1890 , T. lineare Penard, 1890 , Cryptodifflugia oviformis fusca Penard, 1890 .

Type locality: Mikuriga-pond, Murodo, 36º34′46.98″N 137º35′44.97″E; altitude 2,412 m ASL; mountain pine ( Pinus pumila ) vegetation; organic surface layer of soil consisting mainly of fallen needles (coniferous semi-decomposed litter – organic surface soils). Mountain gravelly seasonally freezing soils with high moisture content formed on volcanic rocks.

Type specimen: Laboratory of Soil Bioindication, Department of Soil Geography, Faculty of Soil Science , Lomonosov Moscow State University , slide No. 2-2010 .

Etymology: The new species was named because of the discoid shape of the shell.

Related species – similarities and differences: Assulina discoides is easily distinguished from all other species of the genus Assulina ( Fig. 17 ) by its disk- -shaped shell. In contrast, Assulina scandinavica is almost triangular and has a sharp tapering of the shell from the broad aboral region ( Ogden and Hedley 1980). The new species differs from the brown Assulina muscorum by being colorless, larger in size, and smaller length/width ratio ( Table 3). An important feature is also a monomorphism of the new taxon that allows it to be easily identified in samples with co-occurring congeners, such as Assulina muscorum .

Acknowledgments. The work was supported by the Russian Ministry of Education and Science “State contract No 02.740.11.0283,” Russian foundation for basic research (grant number 11-04-01171- а), and the Japan Society for the Promotion of Science (JSPS), KA- KENHI (No 21310024).

Figures

Fig. 12. Assulina discoides: broad (left) and lateral (right) views. 1–4 – characters of the test measured (see Table 2).

Figs 13–16. SEM (13–15) and LM (16) micrographs of Assulina discoides. 13–14 – broad views; 15 – details of the aperture; 16 – dividing cells.

Fig. 17. Scanning electron microscope images of Assulina muscorum (a), A. seminulum (b) and A. scandinavica (c). The three cells are represented at the same scale. Scale bar: 20 µm (after Lara et al. 2011).