Deharvengia japonica, 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 : 56-59

Deharvengia japonica sp. nov. ( Figs 2–10 ; Table 1)

Description: Test large, colorless, transparent, ovoid to broadly ovoid ( Figs 3, 4 , 7, 8 ), tapering to the front end, dorso-ventrally flattened ( Fig. 10 ), narrowly elliptic in cross-section ( Fig. 9 ). Aperture narrowly elliptic ( Fig. 9 ), with the ventral side cut at about 6/7 of the length of the entire test ( Fig. 10 ), and surrounded by a thin organic lip. There is a small cap on the dorsal side of the shell ( Figs 5 , 7, 10 ), which is surrounded by a narrow organic lip ( Fig. 5 ). Shell is covered by elliptical flat silica plates (idiosomes), about 7 × 11 μm in size and arranged regularly in up to 18 transverse and 13–15 longitudinal rows ( Figs 3, 4 ). On the dorsal side of the cap the direction of the rows follows the outline of the shell ( Fig. 5 ). Flat transparent clavate spines of about 10 μm in length are located on each side of the test between the posterior end and the middle of the test ( Figs 6–8 ).

Shell is large ( Table 1), slightly less than 100 µm in length, which is almost twice the average size of soil testate amoebae. The population is monomorphic. Variation coefficients of all the morphological characteristics are small, ranging between 3.0 and 9.1% for the six morphological variables under investigation ( Table 1).

List of associated testate amoebae. The species 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 , 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 among the mountain pine ( Pinus pumila ) vegetation in the 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. This species was found also in another microhabitat at the same location in tall grasses .

Type specimen: Laboratory of Soil Bioindication, Department of Soil Geography, Faculty of Soil Science , Lomonosov Moscow State University , slide No. 1-2010 .

Etymology: By analogy with the type species Deharvengia papuensis , the new species is named after the country where it was found ( Japan).

Related species – similarities and differences: In comparison with the type species Deharvengia papuensis ( Fig. 11) the new species ( Fig. 2 ) is more dorso-ventrally flattened with an elliptical cross section (axial ratio 2:1); it is broadly ovoid in the broad view; the shell is covered by smaller idiosomes, which are arranged in more than 2 times the number of transverse and longitudinal rows found in the type species. The structure of the dorsal cap differs from those of Deharvengia papuensis ; it is surrounded by a thin organic lip. There are numerous siliceous spines on the sides of the new species, which are absent in type species. Morphology of spines in Deharvengia japonica is unique and different from the spines of all other known species of testate amoebae.

Comments: Both D. japonica and D. papuensis are characterized by a similar structure of their apertural regions ( Figs 7–11 ). This is the main morphological feature which allows uniting them into one genus. Among other morphological characteristics, there are differences, which are listed in the differential diagnosis. According to Bonnet (1979) Deharvengia papuensis with circular cross-section and large idiosomes belongs to the group of species within the genera Sphenoderia and Tracheleuglypha . A new species Deharvengia japonica seems to be morphologically closer to the group of species within the genera Assulina and Placocista , because the shell is laterally flattened, covered with medium-sized idiosomes and has spines. The nature of phylogenetic relations of the genus Deharvengia with these four genera can be determined only by DNA analysis and it is possible that these two species can be separated into two monotypic genera. The degree of morphological differences between these species is as substantial as that between Hoogenraadia and Planhoogenraadia or Ellipsopyxis and Ellipsopixella.

Both species share apparent preferences for similar levels of acidity and moisture of their habitats. They were found in the soils of coniferous forests, which are characterized by pH 4–5 in the soil solution. The new species, unlike Deharvengia papuensis , was found in seasonally freezing soils. In contrast, the type species was described from the soils of the tropical rain forests of conifers Araucaria cunninghami and A. hunsteinii in New Guinea. Araucarias in the New Guinea forests occur in the lower mountain zone up to 1,500 –2,000 m ASL at constant above-zero temperatures. The fact that representatives of this genus ( D. papuensis and D. japonica ) were found exclusively in the mountain soils with precipitation of up to 2,000 mm per year and average temperatures around 20°C ( Balik 1995, Womersley 1995), indicates their affinity to hygrophilous mountain species.

Deharvengia papuensis was viewed as a species with limited geographical distribution ( Foissner 2006). However, the expanding geography of protistological investigations casts new light on the ranges of rare species. Data on the distribution of Deharvengia papuensis are limited, and include the publication of Balik (1995) who discovered this species in the primary mountain rainforest in the Tam-Dao region, in northern Vietnam.

The area of possible distribution of the species from the genus Deharvengia includes Australian and Oriental biogeographic regions (based on classification of Udvardy, 1975). The southern half of the Honshu Is. is in the Japanese evergreen forest province of the Palaearctic biogeographical realm ( Udvardy 1975). It borders subtropical forests, which stretch along the Pacific coast of Indomalaya on the territory of China (Chinese subtropical forest province). This region, according to Hugget (1998) was excluded from the Palearctic and placed into the Oriental region. This viewpoint was supported by Bobrov (2001) based on Gondwanian tropical species from the genera Hoogenraadia and Planhoogenraadia . The finding of a new species provides an additional argument for this pattern and emphasizes the complex Quaternary history of modern ecosystems of this region.

Figures

Fig. 2. Outline of Deharvengia japonica: ventral (left) and lateral (right) views. 1–7 – characters of the test measured (see Table 1).

Figs 3–6. Scanning electron microscopical (SEM) micrographs of Deharvengia japonica.3–4 – dorsal view; 5 – dorsal view of the apertural cap; 6 – flat clavate spines on the side of the test.

Figs 7–10. Light microscopical (LM) micrographs of Deharvengia japonica. 7 – ventral view; 8 – ventro-lateral view; 9 – apertural view; 10 – lateral view.