Proctodrilus tuberculatus ( Černosvitov, 1935 )

Höser, Norbert, 2018, Interrelation of Proctodrilus species (Oligochaeta: Lumbricidae) with lessivage and layering in European soil profiles, Zootaxa 4496 (1), pp. 96-110 : 101-108

Proctodrilus tuberculatus ( Černosvitov, 1935)

In total, 1839 adult individuals were found at 97 localities. They inhabited the finer-grained section of layer boundaries.

• Strössendorf (DE), transect Main floodplain. 50°08'N, 11°14'E. Levee deposits. Profile with bandlike layers. 2 ind. at 17 cm depth, at layer boundary h2 Lu/Ut.

• Kleinkorbetha (DE), transect Saale floodplain. 51°15'N, 12°03'E. Floodplain centre. 16 ind. at 9–55 cm depth, in h1 Lts/Ls3.

• Räpitz (DE), Wiesengraben floodplain. 51°16'N, 12°13'E. Floodplain centre. Profile with bandlike layers. 12 ind. at 4–20 cm depth, in slightly stony h2 Ls3, preferentially at layer boundaries.

• Thronitz (DE), Wiesengraben floodplain. 51°16'N, 12°12'E. Floodplain centre. 1 ind. at 15 cm depth, in wet h4 Ls3.

• Döhlen (DE), transect Wiesengraben floodplain. 51°17'N, 12°12'E. Floodplain centre. Profile with bandlike layers. 6 ind. at 17–35 cm depth, in h3 Ls3. Höser (2015: Fig. 1 ).

• Quesitz (DE), Wiesengraben floodplain. 51°18'N, 12°11'E. Floodplain centre. 2 ind. at 25–30 cm depth, in h4 Ls3.

• Kleinlehna (DE), Renne floodplain. 51°18'N, 12°11'E. Floodplain centre. 1 ind. at 10 cm depth, in h3 Ls3.

• Minkwitz (DE), Weisse Elster floodplain. 51°07'N, 12°13'E. Floodplain centre. Profile layered in parts. 6 ind. at 10 cm depth, in h2 Lts.

• Ostrau (DE), Weisse Elster floodplain. 51°06'N, 12°12'E. Floodplain edge. 16 ind. at> 15 cm depth, in h1 Lts, below a layer inhabited by P. antipai .

• Draschwitz DE), Weisse Elster floodplain. 51°06'N, 12°11'E. Floodplain centre. 4 ind. at 10–20 cm depth, in h1 Lts.

• Profen (DE), Weisse Elster floodplain. 51°08'N, 12°14'E. Floodplain centre. Fossil meander. 6 ind. at 15–40 cm depth, in h2 Lts.

• Zwenkau (DE), transect Alte Elster floodplain. 51°13'N, 12°18'E. Floodplain terrace closest to river. 3 ind. at 12 cm depth, in h1 Lts.

• Eisdorf (DE), Rützschke/Saugraben bottom land. 51°13'N, 12°12'E. Shallow depression at head of valley. 5 ind. at 23–45 cm depth, in h3 Ls3.

• Grossschkorlopp (DE), Krebsgraben floodplain. 51°15'N, 12°14'E. Floodplain centre. 6 ind. at 3–22 cm depth, in h2/3 Ls3.

• Rehbach (DE), transect Krebsgraben depression. 51°16'N, 12°16'E. Shallow depression at head of valley. 5 ind. at 15–22 cm depth, in h0/1 Ls3 of the Al.

• Lobas (DE), Lindenberger Schnauder floodplain. 51°00'N, 12°14'E. Floodplain centre. 2 ind. at 8 cm depth, in h1 Lts.

• Kayna (DE), Grosse Schnauder floodplain. 50°59'N, 12°14'E. Floodplain centre. 2 ind. at 10–15 cm depth, in h1 Lts.

• Oelsen (DE), Grosse Schnauder floodplain. 51°02'N, 12°14'E. Floodplain centre. 5 ind. at 10–15 cm depth, in h1 Lts.

• Brossen (DE), Grosse Schnauder floodplain. 51°02'N, 12°15'E. Floodplain centre. 3 ind. at 10 cm depth, in h2 Lts of the Ah.

• Wintersdorf (DE), Schnauder floodplain. 51°03'N, 12°20'E. Floodplain centre. 1 ind. at> 30 cm depth, in h1 Lts.

• Bosengröba (DE), transect Schnauder floodplain. 51°04'N, 12°22'E. Floodplain centre. 22 ind. at 11–44 cm depth, in h2 Lts. Clay skins present.

• Ruppersdorf (DE), transect Schnauder floodplain. 51°04'N, 12°22'E. Floodplain centre. Profile with bandlike layers. 47 ind. at 5–46, concentrated at 37 cm depth, in slightly gravelly h2 Ls3, which is rustmottled from 30 cm depth.

• Zehma (DE), transect Pleisse floodplain. 50°55'N, 12°26'E. Floodplain edge, foot of slope, fossil levee deposits. 8 ind. at 11–28 cm depth, in h2 Lts of the lower Ah and h1 Lt of the upper aB.

• Selleris (DE), Pleisse floodplain. 50°56'N, 12°25'E. Floodplain centre. Profile with bandlike layers. 2 ind. at 8 cm depth, at layer boundary h2 Ls3/Sl.

• Mockern (DE), Pleisse floodplain. 50°57'N, 12°26'E. Floodplain edge. 5 ind. at 12–28 cm depth, in h2 Lts.

• Ehrenberg (DE), Pleisse floodplain. 50°58'N, 12°27'E. Floodplain centre. 4 ind. at 10–25 cm depth, in h1 Lts.

• Kotteritz (DE), transect Pleisse floodplain. 50°58'N, 12°28'E. Floodplain centre. Profile with bandlike layers. 8 ind. at 20–22 cm depth, at layer boundary h2 Lt/Ls3, over rust-mottled aB.

• Wilchwitz (DE), transect Pleisse floodplain. 50°59'N, 12°29'E. Second floodplain terrace close to river. 10 ind. at 23–27 cm depth, in h1 Lts,> 2 cm over clay-poor aB.

• Schelchwitz (DE), transect Pleisse floodplain. 51°00'N, 12°29'E. Floodplain terrace closest to river. 3 ind. at 14 cm depth, in h2 Lts.

• Kraschwitz (DE), transect Pleisse floodplain. 51°00'N, 12°29'E. Floodplain centre. 5 ind. at 40–52 cm depth, in weakly rust-mottled h0 Lts of the Ba,> 6 cm above Gr.

• Poschwitz (DE), transect slope of depression leading to Pleisse floodplain. 51°00'N, 12°28'E. Lower slope. 24 ind. at 20–41 cm depth, in h1 Lts of the Bt+Al. Höser (2012: Fig. 3).

• Remsa (DE), Pleisse floodplain. 51°00'N, 12°29'E. Floodplain centre. 4 ind. at 16 cm depth, in Lts of the Ah.

• Windischleuba (DE), ten transects Pleisse floodplain. 51°01'N, 12°28'E. Floodplain centre. One profile close to river bandlike, remainder simple layers. 386 ind. at 3–75 cm, mostly at 21–30 cm depth, in h1 Lts. Clay skins present.

• Borgishain (DE), transect Pleisse floodplain. 51°01'N, 12°28'E. Floodplain centre. 23 ind. at 3–45 cm depth, in h1/3 Lts of the Ah/aB or weakly rust-mottled Ah, over clay enrichment.

• Fockendorf (DE), transect Pleisse floodplain. 51°03'N, 12°28'E. Several floodplain terraces. 91 ind. at 3–36 cm depth, in h1/2 Lts, in places over Bg.

• Primmelwitz (DE), transect Pleisse floodplain. 51°03'N, 12°28'E. Floodplain centre. 7 ind. at 20–24 cm depth, in very slightly gravelly h3 Lts.

• Treben (DE), transect Pleisse floodplain. 51°03'N, 12°27'E. Floodplain centre. 21 ind. at 6–40 cm depth, in h1/2 Lts, some at layer boundary to Ls3; also at upper boundary of the aB.

• Plottendorf (DE), transect Pleisse/Gerstenbach floodplain. 51°03'N, 12°27'E. Floodplain centre. 16 ind. at 27–45 cm depth, in h0/1 Lts of the aB. In places P. antipai in overlying layer ( Fig. 1 ).

• Serbitz (DE), transect Pleisse floodplain. 51°04'N, 12°27'E. Floodplain centre. 11 ind. mostly at 16–28 cm depth, in h0/1 Lts, at upper boundary of the aB, singletons at up to 50 cm depth. In places P. antipai in overlying layer.

• Haselbach (DE), two transects Pleisse floodplain. 51°04'N, 12°27'E. Floodplain centre. Profile with bandlike layers. 21 ind. at 3–5 and 25–35 cm depth, in h2/3 Lts, over the aB.

• Gaulis (DE), transect Pleisse floodplain. 51°11'N, 12°24'E. Fossil levee deposits, floodplain centre. Profile with several layers. 9 ind. at 12–37 cm depth, mostly at layer boundary in h2 Ls3, over Sl and aB. In places P. antipai in overlying layer.

• Rötha (DE), Pleisse floodplain. 51°12'N, 12°24'E. Floodplain centre. 1 ind. at 28 cm depth, in h1 Lts.

• Papiermühle (DE), Sprotte floodplain. 50°56'N, 12°24'E. Floodplain centre. 2 ind. at 30–45 cm depth, in h1 Lts.

• Nöbden (DE), transect Blaue Flut floodplain. 50°56'N, 12°21'E. Foot of slope. 3 ind. in wet h2 Lts, at layer boundary in inverse profile.

• Gleina (DE), Blaue Flut floodplain. 50°57'N, 12°24'E. Floodplain centre. 4 ind. in h1 Lts.

• Schlöpitz (DE), transect Blaue Flut floodplain. 50°58'N, 12°23'E. Floodplain centre. 2 ind. at 10–30 cm depth, in h1 Lts.

• Rasephas (DE), two transects Blaue Flut floodplain. 51°01'N, 12°27'E. Floodplain centre. 10 ind. at 10–35 cm depth, in h1/2 Lts. Clay skins present.

• Altenburg (DE), Deutscher Bach floodplain. 51°00'N, 12°26'E. Floodplain centre. 2 ind. in h1/2 Lts.

• Schlauditz (DE), Gerstenbach floodplain. 50°59'N, 12°22'E. Floodplain centre. 1 ind. at 8 cm depth, in h1 Lts.

• Obermolbitz (DE), transect Gerstenbach floodplain. 51°01'N, 12°24'E. Fossil meander. 15 ind. at 27–30 cm depth, in h1 Lts, above intensively rust-mottled Go.

• Untermolbitz (DE), Gerstenbach floodplain. 51°01'N, 12°25'E. Floodplain centre. 3 ind. at h2 Lts. Clay skins present.

• Gerstenberg (DE), transect Gerstenbach floodplain. 51°02'N, 12°26'E. Floodplain centre. 24 ind. at 14–32 cm depth, in h2 Lts to Lt.

• Trebanz (DE), three transects Gerstenbach floodplain. 51°03'N, 12°27'E. Floodplain centre, floodplain edge. Profile partly in bandlike layers. 43 ind. at 16–45 cm depth, in slightly gravelly h2/3 Lts/Lu of the aB and Go. Near floodplain edge under layer with P. antipai .

• Plottendorf (DE), transect Gerstenbach floodplain. 51°03'N, 12°27'E. Floodplain centre, floodplain edge. 21 ind. at 15–26 cm depth, in h1/2 Lts over rust-red aB. Towards floodplain edge P. antipai in overlying layer.

• Leinawald (DE), two transects Teichgraben floodplain. 50°59'N, 12°32'E. Floodplain centre, fossil meander. Profile with bandlike layers. 71 ind. at 4–10 cm depth, in h0/1 Lts above Ls3, in bandlike clay enrichment, above pale grey, slightly rust-mottled Sw; at 4–29 cm depth, in h1 Ls3 above Ss. Clay skins present.

• Lohma (DE), transect Spannerbach floodplain. 50°58'N, 12°32'E. Floodplain centre. 6 ind. at 10–15 cm depth, in rust-mottled h1 Lts, over Lt.

• Pöppschen (DE), five transects Spannerbach floodplain. 51°00'N, 12°30'E. Lower slope, floodplain centre. 125 ind. at 10–35 cm depth, in alluvial fan h1/3 Lts/Ls3, in floodplain centre h1 Lt/Lts; in the Al/Bt, in places reaching Sd, Gro, Go. Clay skins present. Höser (2012: partly in Fig. 2).

• Leinawald (DE), two transects confluence with Wyhra floodplain. 50°58'N, 12°35'E. 10 ind. at 2–15 cm depth, in wet, rust-mottled h2 Lts with clay skins, over Gro, Gr, rust-coloured Go, with clay below.

• Langenleuba-Niederhain (DE), transect Wyhra floodplain. 50°58'N, 12°35'E. Floodplain centre. 1 ind. at 12 cm depth, in h0/1 Lts.

• Streitwald (DE), two transects Wyhra floodplain. 51°02'N, 12°35'E. Floodplain centre. Profile partly layered. 3 ind. at 8–14 cm depth, in h1 Ls3.

• Benndorf (DE), transect Wyhra floodplain. 51°03'N, 12°33'E. Fossil meander at floodplain edge. 26 ind. in area of fossil levee deposits at 8–38 cm depth, in h1/2 Lts, over a layer inhabited by P. antipai ( Fig. 1 and Höser 2008: Fig. 2).

• Beucha (DE), transect Eula floodplain. 51°09'N, 12°35'E. Fossil levee deposits. Profile with several layers. 1 ind. at 17 cm depth, in h0/1 Ls3. Clay skins present.

• Kitzscher (DE), Eula floodplain. 51°09'N, 12°33'E. Floodplain centre. 11 ind. at 12–38 cm depth, in h1 Ls3. Clay skins present.

• Kötteritzsch (DE), transect Mulde floodplain. 51°10'N, 12°48'E. Two floodplain terraces close to river. Profile layered in places. 12 ind. at 4–20 cm depth, in h2 Ls3. Clay skins present.

• Kössern (DE), transect Mulde floodplain. 51°11'N, 12°47'. Floodplain terrace closest to river. Profile with bandlike layers. 70 ind. mostly at 10–25 cm depth, in h1/2 Ls3, concentrated at layer boundaries.

• Nimbschen (DE), Mulde floodplain. 51°13'N, 12°45'E. Floodplain terrace closest to river. 10 ind. at 15–25 cm depth, in h1/2 Ls3.

• Grimma (DE), Mulde floodplain. 51°15'N, 12°44'E. Floodplain terrace closest to river. 18 ind. at 15–40 cm depth, in h1 Ls3.

• Dorna (DE), transect Mulde floodplain. 51°15'N, 12°45'E. Two floodplain terraces close to river. 14 ind. at 15–35 cm depth, in h1/2 Lts/Ls3.

• Neichen (DE), Mulde floodplain. 51°17'N, 12°46'E. Floodplain terrace closest to river. 2 ind. in h1 Ls3, underlying substrate slightly gravelly.

• Nučničky (CZ), Labe (Elbe) floodplain. 50°30'N, 14°13'E. Floodplain terrace closest to river. 15 ind. at 2–30 cm depth, in slightly gravelly to stony h1 Ls3.

• Mlékojedy (CZ), Labe (Elbe) floodplain. 50°32'N, 14°08'E. Migratory confluence with the Ohře. Profile with bandlike layers. 10 ind. at 10–30 cm depth, in h2 Ls3. The layer above inhabited by P. antipai ( Höser 2015: Table 3).

• Dessau (DE), BDF Saalberghau, Elbe floodplain. 51°53'N, 12°12'E. 2 ind. in h1 Us/Ut.

• Dessau (DE), Saalberghau, transect Elbe floodplain. 51°53'N, 12°12'E. Three floodplain terraces close to river. 15 ind. in h1/2 Us, Lu, Lts. Clay skins present in Lts. Höser (2005: Fig. 3).

• Steutz (DE), two BDF, Elbe floodplain. 51°52'N, 12°02'E. 10 ind. in h1 Lts/Lt.

• Steutz (DE), transect Elbe floodplain. 51°52'N, 12°02'E. Middle floodplain terrace. 3 ind. in h2 Lu of fossil floodplain channel. Höser (2005: Fig. 1 )

• Kleneč (CZ), Čepel (Zippel) floodplain. 50°23'N, 14°15'E. Floodplain centre. 4 ind. at 15–25 cm depth, in h2 Lt.

• Söred (HU), transect slope. 47°18'N, 18°18'E. Lower slope, foot of slope. 24 ind. at 5–30 cm depth, in h2/4 Lts and Lt.

• Surduc (RO), transect Someş floodplain. 47°16'N, 23°21'E. Four slightly to medium gravelly floodplain terraces. Profile with several layers. 79 ind. at 5–30 cm depth, on both terraces close to river in Ls3, in places above ferrous hydroxide (limonite) precipitation (Gso); on both terraces away from river in h0/2 Lts with clay skins.

• Tinca (RO), Crişul Negru floodplain. 46°46'N, 21°57'E. Floodplain centre. 2 ind. at 15–22 cm depth, in h1 Lts over gravel layer.

• Porumbenii Mari (RO), transect Tîrnava Mare floodplain. 46°16'N, 25°08'E. Floodplain terrace close to river. 1 ind. at 17 cm depth, in h2 Ls3, at boundary to underlying slightly stony layer.

• Beteşti/Betfalva (RO), transect slope on Fâneaţa Îngustă. 46°18'N, 25°07'E. 18 ind. In loess-loam lessive soil on slope plateau, below the Ah, in uppermost zone of the Al and Bt+Al, mostly at 6–7 cm depth, in h1 Lts/ Lt. Clay skins present. Colluvisol on lower slope, foot of slope, and adjoining basal area with several layers. Species there at 15–37 cm depth, in h1/3 Ls3, Lts. Höser (2016).

• Hoghilag (RO), transect Tîrnava Mare floodplain. 46°14'N, 24°38'E. Floodplain centre. 10 ind. at 10–35 cm depth, in h2 Lts. Clay skins present. In places below a layer containing P. opisthoductus ( Höser 2015: Table 3).

• Săcămaş (RO), transect gorge. 45°54'N, 22°41'E. 6 ind. at 20–35 cm depth, in rust-mottled h1 Ls3. Below a layer with P. opisthoductus , which itself is below a layer with P. antipai ( Fig. 1 ).

• Ilia (RO), transect Mureş floodplain. 45°56'N, 22°39'E. Two floodplain terraces close to river. Profile with bandlike layers. 51 ind. at 7–40 cm depth, in slightly stony h1/2 Ut above Su, preferentially at layer boundary.

• Tisa (RO), transect Mureş floodplain. 45°59'N, 22°27'E. Exterior edge of floodplain terrace closest to river. 1 ind. in h0 Ls3.

• Pojoga (RO), two transects Mureş floodplain. 46°00'N, 22°21'E. Three floodplain terraces close to river. Profile with bandlike layers. 39 ind. at 1–27 cm depth, in h0/1 Ls3, concentrated at boundaries to annual sediment layers. On exterior edge of terrace closest to river P. opisthoductus in the overlying layer.

• Vărădia de Mureş (RO), transect Mureş floodplain. 45°59'N, 22°08'E. Interior edge of floodplain terrace closest to river. 1 ind. in h1 Lts.

• Nicolae Bălcescu (RO), transect Mureş floodplain. 46°01'N, 22°06'E. Floodplain terrace closest to river. 4 ind. in h1 Ls3, below humic horizon with P. opisthoductus .

• Bata (RO), four transects Mureş floodplain. 46°02'N, 22°03'E. Three floodplain terraces close to river. Profile with bandlike layers. 96 ind. at 3–35 cm depth, in h0/2 Ls3, concentrated at boundary to Us or Ss; further from the river in Lts. Clay skins present. In places only at 22 cm depth and below a layer with P. opisthoductus ( Fig. 1 and Höser 2003: p. 104; Höser 2015: Table 3).

• Şoimoş (RO), transect Mureş floodplain. 46°06'N, 21°43'E. Two floodplain terraces close to river. Profile with bandlike layers. 16 ind. at 4–22 cm depth, in h1 Lts and slightly to very gravelly h1 Ls3, mostly at boundary to Ls4. In places at 6–9 cm depth and below a layer with P. opisthoductus ( Höser 2003: p. 104; Höser 2015: Table 3).

• Lipova (RO), transect Mureş floodplain. 46°06'N, 21°44'E. Close to river banks. Profile with several layers. 4 ind. at 5–8 cm depth, in h2 Ls3, over sand.

• Păuliş (RO), transect Mureş floodplain. 46°07'N, 21°34'E. Interior edge of floodplain terrace closest to river. 1 ind. at 20 cm depth, in h1 Ls3.

• Vladimirescu / Glogowatz (RO), transect Mureş floodplain. 46°08'N, 21°24'E. Four floodplain terraces close to river. Profile with bandlike layers. 79 ind. at 4–33 cm depth, in h0/2 Lts, Lu, Ls3. Clay skins present. Höser (2003: Table 3).

• Şomărtin/Martinsberg (RO), transect slope on Pârâul Nou. 45°50'N, 24°38'E. Shallow angle on upper slope. 1 ind. at 14 cm depth, in h0 Lts of the Al/Bt-Horizon. Under a layer with P. opisthoductus .

• Cârţa / Kerz (RO), transect Olt floodplain. 45°47'N, 24°35'E. Floodplain terrace closest to river. 2 ind. at 17 cm depth, in h1 Lts. Clay skins present.

• Valea Stanciului (RO), transect Jiu floodplain. 43°58'N, 23°53'E. Second floodplain terrace close to river. 1 ind. at 18 cm depth, in h0/1 Lu, at layer boundary to Ls3.

• Zăval (RO), transect Jiu floodplain. 43°50'N, 23°49'E. Floodplain terrace closest to river. 2 ind. at 30 cm depth, in h0/1 Ls3.

Habitat specifity of Proctodrilus species. Our observations suggest that the occurrence of Proctodrilus species is not correlated with certain soil types but rather with the structure and the biological state of the soil profiles. Therefore their relation to soil horizons and layers will be considered in the following. The Proctodrilus species live mainly in sites/habitats that show the influence of sedimentation and erosion, e.g. the soils of floodplains and slopes. They organise themselves into occupying different parts of the soil profile according to the type of soil preferred, shaped by factors such as gradient of hydromorphology, or particle size, or in the various layers created by sedimentation.

P. antipai was exclusively recorded in floodplain soils: cohesive, clay-rich Ah-horizon ( Zicsi 1959; Höser 1986), and regularly above or at the upper boundaries of the oxidation horizons of gleys (Go, Gro, Ah-Go). Occasionally the species appears near the surface in wet gleys (Go-Ah). Thus it inhabits the region of fluctuating groundwater levels, including the upper boundary of the capillary water fringe. These types of soil habitats occur mainly at floodplain edges, though also at the valley bottoms along streams. P. antipai avoids reduction horizons (Gor, Gr), being found above the upper boundary of clay-rich impervious horizons (Sd) or of the B-horizons. In floodplains it occupies the exterior edges of the terraces closest to the valley slope, immediately at the edge of the floodplain or in floodplain channels and fossil meanders. Using the moisture classification of Schlichting et al. (1995), the species lives in wet to moist habitats (pF 1–2), i.e., clearly separate from the other three species (see below). In summer their habitat has a closed capillary fringe at 3–8 dm below surface (= high to moderately high), and small to moderate oscillations of the ground water level. In contrast, P. tuberculatus was always found in damp to moist soils (pF 2–3) with a very low and strongly oscillating capillary fringe during summer (> 15 dm below soil surface).

In the floodplains P. opisthoductus prefers the fine-grained, humus-rich, rather thin sedimentary layers in soils without gley horizon, and is present in the colluvial topsoils on slopes. It is commonly found in the matted vegetation roots (Aw) of the sediments close to the surface. In floodplains its preferred habitat corresponds roughly to that part of the valley bottom that is regularly inundated by floodwater, mostly excluding the interior edge of the terrace closest to the river.

Most P. tuberculatus individuals were found in areas of clay-poor and clay-skin-bearing horizons (Al, Bt). This species occurs regularly in the clearly layered soils that are well removed from groundwater and exist in floodplains in the vicinity of the river (Fluvisoliment-Bänder, Schirmer 1983), or were near the river during floodplain creation ( Höser 2008). Therefore P. tuberculatus mostly occurs at the interior edge of the terrace closest to the river, where coatings of clay (containing additional silt and humus) are rapidly formed in the sediment during periodic flooding ( Gerrard 1981). In the slope catena it prefers the Al-horizon on the upper slope, though it is also found in low-gradient slopes and in the inverse profile on the lower part and foot of slopes ( Höser 2012, 2016).

P. thaleri was found on slopes (Celei) as well as in the floodplain (Copşa Mică). According to the present finds, P. tuberculatus and P. thaleri live under geomorphologically similar site conditions, although in fact the two species are mutually exclusive. Therefore we hyothesize that the habitats of the two species differ fundamentally in the degree of lessivage.

Separation of the species in the layered soil profile. In some parts of the floodplains and slopes, assemblages of P. antipai , P. opisthoductus , and P. tuberculatus linked to distinct soil profile layers are conspicuous ( Fig. 1 ). One profile (Săcămaş) contains these three species in the order shown above, from top to bottom, each in a different layer. There was no observation of any association between the species. Profiles were regularly found in which two species were living, each in a different layer. Seven cases from central Germany and northern Bohemia are known in which the layer occupied by P. antipai lies above that containing P. tuberculatus (Ostrau, Serbitz, Gaulis, Trebanz, Mlékojedy, two near Plottendorf). In one further profile the relation between the two species is reversed (Benndorf). In this instance the soil profile was of fossil levee deposits that probably were accumulated by a free meander in the course of its cutting through the floodplain edge ( Höser 2008). In six cases in Romania (Hoghilag, Pojoga, Nicolae Bălcescu, Bata, Şoimoş, Şomărtin) P. opisthoductus occurs above the layer inhabited by P. tuberculatus ; here the population of P. opisthoductus is occasionally concentrated at the lower end of the vegetation-root mat (Aw). The vertical order of species in the stratified soil profile (e.g. the profile in Săcămaş, see Fig. 1 ) demonstrates that P. antipai and P. opisthoductus occur in younger layers and that P. antipai prefers the sediments richest in organic matter. Here different and species-specific ressource requirements and physically induced habitat constraints become evident. Hence in this genus there is, in addition to morphological separation, a similarly clear ecological species separation ( Höser 1997).

Preference for layer boundaries as a taxonomic characteristic of the genus. The four Proctodrilus species prefer proximity to the layer boundaries in the soil profile, where they are met with on the side where the substrate particles are finer ( Fig. 1 ). This is most striking in P. tuberculatus , and well seen in more than 13 out of 97 study sites. Such assemblages were also recorded for P. thaleri (near Copşa Mică) and P. opisthoductus (near Valea Lungă, Spini, Dobra, Bata). P. antipai appears in higher numbers not only at layer boundaries (Immelborn, Kotteritz, Deutsches Holz, Břežany nad Ohři) but also in thin water-conducting horizons (Sw). The four species mostly occur above fluctuating groundwater levels, where temporary minima of soil moisture occur, for example for P. tuberculatus at the interior, generally clearly layered edges of floodplain terraces close to the river ( Höser 2003: Table 3). In such locations the capillary water of the layer boundaries will be a sufficient water supply. This water forms in the lower part of the fine-grained substrate that overlies a coarser-grained one (“hängendes Kapillarwasser”: Mückenhausen 1993). In addition, the clay-rich habitat of P. antipai is mostly reached by the capillary limit of the groundwater. The four Proctodrilus species are adapted to temporary minima of soil moisture by their enteronephric excretory system ( Rosa 1906, Zicsi 1985), by which they are able to retain water and reabsorb it through the intestine ( Bahl 1947, Stolte 1969).

Distributional range of the species. The species records presented here lie within the currently known distributional ranges ( Bouché 1972; Csuzdi & Zicsi 2003; Csuzdi et al. 2006, 2011; Hackenberger Kutuzović & Hackenberger Kutuzović 2013; Lehmitz et al. 2014; Mršić 1991; Pižl 2002; Plisko 1973; Pop et al. 2012; Stojanović & Milutinović 2014; Stojanović et al. 2013; Valchovski 2012; Zicsi 1994). These authors and our records make clear that among the four Proctodrilus species P. tuberculatus and P. antipai occupy the widest range and extend farthest to the north (to northern central Europe), while P. opisthoductus does not reach the border of the German uplands. P. thaleri has the narrowest distribution of a Carpathian endemic, as established by Pop et al. (2012). As regards the zoogeographical categorisation in chorological types, P. tuberculatus is a transaegian species while P. antipai and P. opisthoductus are Central European species ( Csuzdi et al. 2011; Pop et al. 2012).

The distribution center of the four Proctodrilus species is the European region of terrestrial soils influenced by lessivage ( Ganssen & Gračanin 1972; Ganssen & Hädrich 1965). Furthermore, floodplains also offer habitats with similar properties ( Kopp 1964). The lessivage processes result in the leaching of clay, analogous to the process in floodplain soils where sedimentation and floodplain dynamics result in clay migration ( Kopp 1964). P. tuberculatus (in Bt+Al) clearly prefers such clay-poor horizons of the stratified soil profiles on slopes and the interior edges of floodplain terraces, while P. antipai (in Ah-Sw) inhabits favourable bands in the sedimented strata of the clay-rich floodplain edge. In this way both species occupy a Europe-wide range.

In north- central Europe, where lessivage took place in several phases during the late glacial period and the Holocene ( Kundler 1961; Lieberoth 1982), the clay-leached horizons occurring in the terrestrial domain are mostly relicts ( Reuter 2001; Kühn 2003). Characteristics indicating recent lessivage that derive from the earlier stage of brown loam (terra fusca) are lacking there ( Reuter 1964a). P. tuberculatus apparently prefers such soils, where lessivage is advanced, almost complete, or a relict of previous pedogenetic processes. Clearly recent lessivage is evident under warm climatic conditons, e.g. in southeast Europe ( Reuter 1964b, 1999), where P. opisthoductus and P. thaleri are found. Apparently P. opisthoductus and P. thaleri are tied to horizons in different layers in which the drainage of the clay-complexes of a brown loam character ( Kubiena 1956) is still ongoing, in other words in horizons of recent lessivage in the warm-humid climate of southeast Europe. This explains the geographic location of their distribution areal and leads to the hypthesis that P. thaleri occurs only in those parts of Europe where—due to ongoing (recent) lessivage in soil profiles—active flow-plasma is present in highest concentrations. Pathways in the soil structure created by lessivage ( Kubiena 1956), and also by other similarly clay-filled inhomogeneities of lessived floodplain soils such as fractures of the soil aggregate apparently favour these four small Proctodrilus species in their movement through the soil column ( Höser 2008).

Figures

FIGURE 1. Ecological species separation in the genus Proctodrilus: Soil profiles with two or three co-occurring species, each in a different layer. For further details see text. Bottom right: Generalized scheme of preferred occurrence of Proctodrilus species in the soil profile: close to layer boundaries and in the layer with finer particle size.