Species characterization and previous occurrences

Arcella conicaDeflandre, 1928

Autogenous brown test. Hexagonal in ventral view with a central, circular aperture. Domed in lateral and dorsal view with depressions forming angular facets bordered by prominent folds and flattened vertices (Figure 2A). This is the first record of this species in Mexico.

Arcella dentata Ehrenberg, 1830

Autogenous colorless or yellow test. Circular in ventral view, with 9 to 14 spine-like projections that either formed incipiently or were well developed. Aperture: circular and central. Shallow-bowl shaped in lateral view with flattened vertex and 9 to 14 ridges in dorsal view (Figure 2B, Figure 2C, Figure 5A). The species was observed previously in Mexico in a semipermanent freshwater body (^{Tiscareño, 2008}).

Arcella discoidesEhrenberg, 1843

Autogenous test, colorless, yellow, brown, white, red or black. Circular in ventral view with a smooth surface. The aperture is circular, invaginated and bordered by a shallow lip, usually surrounded by a ring of numerous small pores. Plano-convex in lateral view, sometimes arched with a basal border (Figure 2D, Figure 2E, Figure 5B). The species was previously observed in Mexico in lakes, springs and wetlands (^{López-Ochoterena & Roure-Cane 1970}; ^{Bobrov et al., 2013}).

Arcella gibbosa Penard, 1890

Autogenous yellow test. Circular in ventral view. Test surface is irregular with numerous small pores between the circular plates. Aperture invaginated, circular and with a distinct lip. Hemispherical in lateral view, with regular depressions on the dorsal surface (Figure 2F, Figure 2G, Figure 5C). The species was observed previously in Mexico in lakes and wetlands (^{Aladro et al., 2007}; ^{Bobrov et al., 2013}).

Arcella megastomaPenard, 1902

Autogenous yellow or brown test. Circular in ventral view. Wide aperture with a small lip surrounded by small pores. Flattened in lateral view (Figure 2H, Figure 2I, Figure 5D). The species was observed previously in Mexico in springs, lakes and wetlands (^{López-Ochoterena & Madrazo-Garibay, 1979}; ^{Bobrov et al., 2013}).

Arcella vulgaris Ehrenberg, 1830

Autogenous yellow or brown test. Circular in ventral view, with an invaginated, circular aperture bordered by a small lip. Smooth surface test with plates and numerous fine pores between them. Hemispherical in lateral view, often with a basal collar (Figure 2J, Figure 5E). This species has a broad distribution in Mexico and has been observed in springs, lakes, semipermanent freshwater bodies, cave pools, cenotes, drinking water, wastewater, wetlands, rice paddies and soil (^{Osorio-Tafall, 1943}; LópezOchoterena & Roure-Cane, 1970; ^{Rico-Ferrat & López-Ochoterena, 1976}; ^{Tomasini-Ortiz & López-Ochoterena, 1979}; ^{Serrano-Limón & López-Ochoterena, 1992}; ^{Aladro et al., 2007}; ^{Tiscareño, 2008}; ^{van Hengstum et al., 2008}; ^{Bobrov et al., 2013}).

Argynnia triangulata Deflandre, 1936

Xenogenic brown test. Trapezoid shape in lateral view, with the fundus larger than the aperture. Aperture terminal and circular. Test surface smooth with regular and flattened mineral aggregates (Figure 2K). This is the first record of this species in Mexico.

Centropyxis aculeata

Ehrenberg, 1832 var. aculeata

Xenogenous yellow or brown test. Ovoid or circular and depressed in ventral view, with 4-10 posterolateral spines. Aperture subterminal, circular or oval and invaginated. Capshaped in lateral view and tapers toward the aperture. Test surface is smooth only around the aperture and is covered near the spines and on the dorsal surface with mineral grains or diatom frustules (Figure 2L, Figure 2M, Figure 2N, Figure 5F, Fig 5G). This variety was observed previously in Mexican cenotes (^{van Hengstum et al., 2008}).

Centropyxis aculeata

Ehrenberg, 1832 var. discoides

Xenogenous yellow or brown test. Ovoid or circular, depressed in ventral view and without spines. Aperture sub-terminal, circular or oval and invaginated. Main body hemispherical in lateral view with pronounced tapering toward the aperture. Test surface is rough and often covered with mineral grains (Figure 2O, Figure 2P, Figure 5H). This variety was observed previously in Mexican cenotes (^{van Hengstum et al., 2008}).

Centropyxis constricta

Ehrenberg, 1843 var. aerophila

Xenogenous yellow or brown test. Ovoid in ventral view. Aperture sub-terminal, circular or ovoid, invaginated and with a semi-circular rim. Spherical in lateral view and slightly flattened towards the aperture. The test surface is generally rough with mineral grains or diatom frustules and smooth only in a small region around the aperture (Figure 2Q, Figure 2R, Figure 5I). This variety was observed previously in Mexican cenotes (^{van Hengstum et al., 2008}).

Centropyxis constricta

Ehrenberg, 1843 var. constricta

Xenogenous yellow or brown test. Ovoid in ventral view, with 2 or 3 spines on the fundus. The aperture is sub-terminal, ovoid, invaginated and with a semi-circular rim. Spherical in lateral view and slightly flattened towards the aperture. The test surface is rough with mineral grains (Figure 2S). This variety was observed previously in Mexican cenotes (^{van Hengstum et al., 2008}).

Centropyxis constricta

Ehrenberg, 1843 var. spinosa

Xenogenous yellow or brown test. Ovoid in ventral view, with 2-6 spines on the fundus. Aperture sub-terminal, ovoid, invaginated and with a semi-circular rim. Spherical in lateral view and flattened towards the aperture. The test surface is rough with mineral grains or diatom frustules (Figure 2T, Figure 2U, Figure 2V). This is the first record of this variety in Mexico.

Centropyxis deflandrei Rampi, 1950

Xenogenous brown test. Circular in ventral view and laterally depressed. Aperture ovoid to circular and sub-terminal, almost half the size of the test. Without spines. Test surface with mineral grains or diatom frustules (Figure 2W). This is the first record of this species in Mexico. A similar species (Centropyxis cf. deflandrei), however, was reported previously in soils and wetlands (^{Bobrov et al., 2013}).

Centropyxis ecornis Ehrenberg, 1841

Xenogenous circular to square brown test. Circular in ventral view, flattened in lateral view. Large aperture, almost quadrate and sub-terminal, without spines. Test surface with mineral grains (Figure 2X). Species previously observed in Mexico in lakes, waterfalls, wetlands and soil (^{Laminger, 1973}; LópezOchoterena & Madrazo-Garibay, 1979; ^{Bobrov et al., 2013}).

Cucurbitella tricuspisCarter, 1856

Xenogenous brown test. Spherical to vaseshaped in lateral view, with a terminal, circular and crenulated aperture. Often with a thin lip surrounded by a 5-11-lobe collar. Test surface with mineral grains or diatom frustules (Figure 3A, Figure 3B, Figure 5J, Figure 5K, Figure 5L). This is the first record of this species in Mexico.

Cyclopyxis kahli Deflandre, 1929

Xenogenous brown test. Circular in ventral view, with a circular and central aperture. Hemispherical in lateral view. Aperture surface slightly invaginated and smooth. The dorsal surface is rough with mineral grains (Figure 3C, Figure 3D). Species previously observed in Mexico, in lakes, mosses, wetlands and soils (^{Golemansky, 1967}; ^{Bonnet, 1977}; ^{Bobrov & Krasil'nikov, 2011}; Bobrov et al., 2013). Cyphoderia ampulla Ehrenberg, 1840

Autogenous brown test. Ovoid in lateral view, with round base and tapered near the aperture, forming a short, retort-shaped neck. Aperture terminal and circular. The surface test is composed of oval plates on an organic matrix (Figure 3E, Figure 5M). Species previously observed in a lake in Mexico (^{Bobrov et al., 2013}).

Difflugia labiosa

(Leidy, 1874) Penard, 1902

Xenogenous brown test. Pyriform in lateral view. Fundus tapers slightly to a rounded eccentric apex, with a thin collar surrounding the aperture, which is terminal and circular. Small mineral grains on the surface test (Figure 3F). This is the first record of this species in Mexico.

Difflugia distenda

Gauthier-Lièvre and Thomas, 1958

Xenogenous test with colorful mineral grains. Almost spherical, with two symmetrical hornlike spines at the fundus. Thin collar with small mineral grains and terminal aperture (Figure 3G). This is the first record of this species in Mexico.

Difflugia bidensPenard, 1902

Xenogenous brown test. Ovoid and laterally compressed, with 2-5 small spines at the fundus. Aperture terminal, circular and large, without a collar. Some spines can be bifurcated. Test surface with relatively smooth mineral grains (Figure 3H, Figure 3I, Figure 3J). This is the first record of this species in Mexico.

Difflugia coronaWallich, 1864

Xenogenous brown test. Ovoid to spherical in lateral view, with 1-4 spines at the fundus. Some spines can be bifurcated. Aperture terminal, circular and surrounded by a collar with 8 -12 lobes composed of small particles cemented together. Test surface formed of small mineral grains or fragments of diatom frustules (Figure 3K, Figure 3L, Figure 5N). Species previously observed in Mexico in lakes and in a reservoir (^{López-Ochoterena & Roure-Cane, 1970}; ^{Serrano-Limón & López-Ochoterena, 1992}; ^{Silva-Briano et al., 2007}).

Difflugia fragosaHempel, 1898

Xenogenous, yellow or brown test. Elongated, with 3-5 large projections running from the middle of the test to the fundus, forming wide spines or tubercles. Aperture terminal and circular, with a thin collar. Test surface formed of small mineral grains (Figure 3M, Figure 3N). This is the first record of this species in Mexico.

Difflugia gramenPenard, 1902

Xenogenous, yellow or brown test. Test ovoid or spherical in lateral view. Aperture terminal and lobed, in general with 3 lobules and a thin lip made of small particles cemented together. Test surface formed of small mineral grains (Figure 3O, Figure 3P, Figure 5O). Species previously observed in Mexico in lakes, wetlands and wastewater (^{López-Ochoterena & RoureCane, 1970}; ^{Rico-Ferrat & López-Ochoterena, 1976}; ^{Serrano-Limón & López-Ochoterena, 1992}; ^{Bobrov et al., 2013}).

Difflugia oblonga

Ehrenberg, 1832 var. bryophila

Xenogenous, brown test. Pyriform in lateral view, with a conical fundus. Aperture terminal and circular, formed by mineral grains cemented together, without a collar. Test made of coarse sand grains (Figure 3Q, Figure 3R, Figure 5P). This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. glans

Xenogenous, brown test. Ovoid in lateral view, with a rounded fundus. Aperture terminal, large, circular and formed by mineral grains cemented together, without a collar. Test made of coarse sand grains. This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. lanceolata

Xenogenous, brown test. Pyriform in lateral view, with a rounded fundus. Aperture terminal, circular and formed by mineral grains cemented together, without collar. Test made of small mineral grains (Figure 3S). This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. linearis

Xenogenous, brown test. Ovoid and elongated in lateral view, with a conical fundus. Aperture terminal and circular, without a collar, formed by mineral grains cemented together. Test made of small mineral grains (Figure 3T). This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. oblonga

Xenogenous, brown test. Pyriform and elongated in lateral view, with a large neck and rounded fundus. Aperture terminal, circular and formed by mineral grains cemented together. Test composed of angular sand grains and diatom frustules (Figure 3U, Figure 3V). This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. spinosa

Xenogenous, brown test. Pyriform and elongated in lateral view, with a short or long neck and a spine on the fundus. Aperture terminal, circular and formed by mineral grains cemented together. Test composed of angular sand grains and diatom frustules (Figure 3W, Figure 3X). This is the first record of this variety in Mexico.

Difflugia oblonga

Ehrenberg, 1832 var. tenuis

Xenogenous, brown test. Pyriform and elongated in lateral view, without a neck and a truncated fundus. Aperture terminal and circular, formed by mineral grains cemented together. Test composed of angular sand grains and diatom frustules (Figure 4A, Figure 4B). This is the first record of this variety in Mexico.

Difflugia protaeiformis

Lamarck, 1816 var. acuminata

Xenogenous, hyaline to brown test. Cylindrical in lateral view, with slight tapering near the aperture and a dorsal spine sometimes very large and slightly curved. Aperture terminal and circular, with a smooth outline. Test made of mixed-size mineral grains or diatom frustules (Figure 4C, Figure 4D, Figure 4E, Figure 5Q). This is the first record of this variety in Mexico.

Difflugia protaeiformis

Lamarck, 1816 var. amphoralis

Xenogenous, yellow to brown. Elongated test, almost biconical in lateral view, narrowing toward the aperture and with a large projection in the dorsal region that forms one or two wide spines. Aperture terminal and circular, with a smooth outline and a short collar. Test made of coarse grains (Figure 4F, Figure 4G). This is the first record of this variety in Mexico.

Difflugia protaeiformis

Lamarck, 1816 var. claviformis

Xenogenous, opaque test. Cylindrical in lateral view, slightly tapering near the aperture and with a wide spine in the dorsal region. Aperture terminal and circular, with a smooth outline. Test made of coarse grains (Figure 4H). This is the first record of this variety in Mexico.

Difflugia urceolata

Carter, 1864 var. elongata

Xenogenous, brown and opaque test. Ovoid in lateral view, with a rim sometimes pronounced and curved. Some specimens can have wide spine-like protuberances. Aperture large, terminal and circular, with a relatively smooth outline. Test made of mixed-size grains or diatom frustules (Figure 4I, Figure 4J, Figure 5T). This is the first record of this variety in Mexico.

Difflugia urceolata

Carter, 1864 var. urceolata

Xenogenous, brown and opaque test. Spherical in lateral view, with a pronounced rim that curves back on itself. Occasional wide, spine-like protuberances. Aperture large, terminal and circular with a relatively smooth outline. Test made of mixed-sized grains or diatom frustules (Figure 4K, Figure 4L). This is the first record of this variety in Mexico.

Euglypha acanthophora Ehrenberg, 1814

Autogenous hyaline test. Ovoid in lateral view, with a rounded fundus. Aperture terminal and circular. Test composed of oval to hexagonal plates.Those forming the aperture display a serrated, V-shaped edge, with 5-7 teeth bordering each of these margins. Some dorsal-region plates project dorsally like spines, and can be up to three times the size of the plates themselves (Figure 4M, Figure 5R). Species previously observed in Mexico in lakes and wetlands (^{Aladro et al., 2007}; ^{Bobrov et al., 2013}).

Lesquereusia modestaRhumbler, 1895

Autogenous, hyaline to brown. Spherical in lateral view, with an asymmetrical neck, and laterally, slightly narrow. Aperture terminal and circular. Test surface composed of small mineral grains (Figure 4N). Species previously observed in Mexican high-mountain lakes (^{Laminger, 1973}).

Lesquereusia spiralis Ehrenberg, 1840

Autogenous, brown test. Spherical in lateral view, with an asymmetrical neck and laterally, slightly narrow. Spine-like dorsal projection. Aperture terminal and circular. Test surface composed of numerous curved rods (Figure 4O, Figure 5S). This is the first record of this species in Mexico.

Pentagonia maroccana

Gauthier-Lièvre and Thomas, 1958

Xenogenous brown test. Elongated in lateral view, with four short, wide, spine-like projections on fundus. Short collar and terminal aperture. Surface with small mineral grains (Figure 4P). This is the first record of this species in Mexico.

Pseudodifflugia fulva Archer, 1870

Xenogenous brown test. Spherical in lateral view, with a very irregular shape because of the large agglutinated particles. Aperture circular, large and smooth in ventral view (Figure 4Q, Figure 4R, Figure 4S). This is the first record of this species in Mexico.

Scutiglypha cabrolae

Smet and Gibson, 2009

Autogenous test. Plates of different shape depending on the row level. Plates in row around aperture with a triangular edge forming a serrated margin. The opposite end of the plate is semi-circular in shape. Rows of plates increasingly distant from the aperture have decreasingly rounded upper edges, culminating in generally small, but sometimes longer and wider spines in the rows at the fundus (Figure 4T). This is the first record of this species in Mexico.

Taxa distribution in lakes: The greatest number of taxa found in a single lake (No. 4) was 18, and only one lake (No. 6) had no individuals. (Species richness in each lake was tabulated in Appendix I). On average, we recorded eight taxa in each lake. The most-observed taxon was Centropyxis aculeata var. aculeata, observed in 22 of the 29 lakes, followed by Arcella discoides, recorded in 17 lakes. In contrast, eight species were recorded in only one lake (Arcella conica, Centropyxis deflandrei, C. ecornis, Cyphoderia ampulla, Difflugia distenda, Lesquereusia spiralis, Pseudodifflugia fulva and Scutiglypha cabrolae). The most similar lakes in terms of species composition were lakes No. 1 and 19, which shared 10 species. Specific richness of testate amoebae in the lakes does not seem to be associated with water depth or lake altitude, so other environmental variables should be explored.