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Protistology 11 (1), 20-36 (2017)
Protistology
Morphological variability of Padaungiella lageniformis (Arcellinida: Padaungiellidae) from the central part of the Balkan Peninsula
Stefan Luketa
University of Novi Sad, Faculty of Sciences, Department of Biology and Ecology, Novi Sad, Serbia
| Submitted January 19, 2017 | Accepted February 25, 2017 |
Summary
The genus Padaungiella includes five species characterized by flask-shaped shells covered by predated or collected plates. Padaungiella lageniformis is the type species with cosmopolitan distribution. In this paper, morphological variability of P. lageniformis based on three populations from the central part of the Balkan Peninsula is presented. A specimen characterized by the pointed shell fundus was observed. Also, several specimens completely covered by square plates were registered; therefore, taxonomic status of Nebela cordiformis and Quadrulella lageniformis are discussed. In one studied population, shells with very long neck (up to 55 ^m) were observed and thus relations of P. lageniformis with P. wetekampi are discussed. It is concluded that shell width/shell length ratio is a very important taxonomic character for distinguishing P. lageniformis (0.45—0.67) and P. nebeloides (0.34—0.46). In addition, synonymizing of P. wailesi with P. lageniformis is proposed.
Key words: biometry, morphometry, protists, taxonomy, testate amoebae
Introduction
The family Padaungiellidae was recently established for three closely related genera characterized by an elongated neck: Alocodera, Apodera and Padaungiella (Luketa, 2015). These testate amoebae have rigid, flask-shaped shells covered by predated siliceous oval or quadrangular plates. The aperture is terminal and bordered by a thick organic lip. This family comprises nine moss-dwelling species, six of which are poorly studied by morphometric methods: so far, only three studies have been dealing with the morphological variability of padaungiellid testate amoebae (Zapata and Fernández, 2008; Todorov et al., 2010; Luketa, 2015).
Jung (1942a) proposed the genus Schaudinnia for Nebela species with an elongated neck. As Jung's classification lacks type designations, the name Schaudinnia is unavailable. Based on molecular data, Kosakyan et al. (2012) placed members of the genus Nebela with an elongated neck into a separate genus named Padaungiella. These authors included into the genus Padaungiella three very common species (P. lageniformis, P. tubulata and P. wailesi) and two rare species (P. nebeloides and P. wetekampi). Taxonomy at the species level within this genus is predominantly based on morphometric data. For example, P. tubulata, P. wailesi and P. lageniformis have very similar morphology, but shell length is the key character for distinguishing these
doi:10.21685/1680-0826-2017-11-1-2 © 2017 The Author(s)
Protistology © 2017 Protozoological Society Affiliated with RAS
species. In addition, P. lageniformis and P. wetekampi also have very similar morphology, but neck length is the key character for distinguishing these species.
In the present paper, I report the results of morphometric analysis of testate amoebae from three P. lageniformis populations from the central part of the Balkan Peninsula and discuss the taxonomic status of some closely related species.
Material and methods
The material for the present study was collected from three localities in the central part of the Balkan Peninsula (Table 1). Morphological characters and morphometric variables were studied using a light microscope Zeiss Axio Imager A1. Images were captured using an AxioCam MRc5 (Zeiss) digital color camera. Measurements were conducted in the program AxioVision 4.9.1. The following shell parameters were measured: shell length, shell width, aperture width, neck length, neck width (Fig. 1), and area of the optical section (area enclosed by the outline of the shell). The following descriptive statistics were calculated: extreme values (minimum and maximum), median, arithmetic mean, standard error of the arithmetic mean, standard deviation, coefficient of variation (in percentage), skewness and kurtosis. Statistical analysis was conducted using the programs PAST 2.17c and STATISTICA 13.0.
Results
Description of the species
The shell is transparent, colorless or slightly yellow, pyriform, always laterally compressed, rounded aborally, prolonged into a tubular neck. I found one specimen with the pointed shell fundus in Sphagnum-dwelling population from the Alagovac Lake region (Fig. 2). The shell is covered by a mixture of predated or collected oval, circular, elongated and quadrangular plates; these plates are usually arranged haphazardly and overlap. Several specimens in population from Sargan Mountain have shells covered mainly by quadrangular plates (Fig. 3). The aperture is oval or like an elongated slit and it is surrounded by a thick organic lip. It is characterized by an uneven and undulating rim. Namely, in frontal view the apertural lip is convex, while in lateral view it is concave.
Fig. 1. Shell outline of Padaungiella lageniformis and position of the measured axes. A — shell length; B — shell width; C — aperture width; D — neck length; E — neck width.
Population from Sargan Mountain
Morphometric characters of 49 specimens from Sargan Mountain were measured and the results are given in Table 2. Figure 4 shows light micrographs of specimens from this population. The most frequent shell length (131 ^m) was registered in 5 specimens (Fig. 5A); the most frequent shell width (72 ^m) was registered in 6 specimens (Fig. 5B), and the most frequent aperture width (28 ^m) was registered in 14 specimens (Fig. 5C). Coefficient of variation was moderate for area of the optical section (13.75%), while the other measured variables were characterized by low variability (from 4.88% to 9.98%). For basic characters, the minimal variability was observed for aperture width (6.89%), while the maximal variation coefficient was observed for neck length (9.98%). For ratio characters, the minimal variability was observed for shell width/shell length ratio (4.88%), while the maximal variation coefficient was observed for neck width/neck length ratio (9.58%).
Analysis of the size frequency distribution of shell length, shell width and aperture width indicates that this population is size-monomorphic. Shell length ranged from 101 to 153 ^m. However, 71.43% of all measured specimens had a shell length of 122-138 ^m, whereas only 14.29% were smaller than 122 ^m and only 14.29% were larger than 138
Fig. 2. Specimen of Padaungiella lageniformis with pointed fundus of the shell observed in a Sphagnum-dwelling population from the Alagovac Lake region, East Herzegovina. Scale bar: 20 ^m.
^m. The frequency analysis of the shell width shows similar distribution pattern. Namely, all measured specimens had shell width ranging between 56 and 90 ^m. In this case, 83.67% of all specimens had shell width of 69-80 ^m, whereas only 8.16% were narrower than 69 ^m and only 8.16% were wider than 80 ^m. Figures 5D-F show bag plots analyses of the correlation between shell length, shell width and aperture width.
The positive value of skewness for seven characters suggests an asymmetrical distribution with a long tail toward higher values. The asymmetry of aperture width, area of the optical section, neck width/shell length ratio, and neck width/neck length ratio was low, with skewness values ranging between 0.018
Fig. 3. Specimen of Padaungiella lageniformis with shell covered mainly by quadrangular plates observed in a moss-dwelling population from Sargan Mountain. Scale bar: 20 ^m.
and 0.205. Moderate positive values of skewness (0.260—0.381) were observed for shell width/shell length ratio and aperture width/shell width ratio. High positive skewness value (1.200) was observed only for aperture width/shell length ratio. All other variables were characterized by negative values of skewness (between -0.013 and -1.032), indicating a distribution with a long tail toward the lower values.
Two characters (aperture width/shell width ratio and neck length/aperture width ratio) displayed negative kurtosis values, meaning that they were characterized by flatter distribution than a standard Gaussian distribution. Since the negative value obtained for neck length/aperture width ratio (-0.215) is not clearly different from zero, the
Table 1. List of sampling locations of the examined populations of Padaungiella lageniformis from the central part of the Balkan Peninsula
Microhabitat Location Country Coordinates Date of collection
epigenous mosses Sargan Mountain Serbia 43°49'40.10''N, 19°31'41.40"E August 17, 2016
epigenous mosses Alagovac Lake region Bosnia and Herzegovina 43°17'05.9''N, 18°07'58.7''E July 24, 2016
Sphagnum mosses Alagovac Lake region Bosnia and Herzegovina 43°17'44.8''N, 18°07'31.9''E April 18, 2014 August 19, 2014 May 11, 2016 July 24, 2016
Fig. 4. Light micrographs of Padaungiella lagenifortms. broad lateral view of different specimens from Sargan Mountain, Serbia. Scale bars: 20 ^m.
Table 2. Morphometric characterization of moss-dwelling population of Padaungiella lageniformis from Sargan Mountain (Serbia) based on 49 specimens (measurements in |jm, except for area of the optical section in jm2)
Characters Min Max M x SE SD CV Sk Ku
shell length 101 153 131 129.67 1.42 9.95 7.67 0.564 1.323
shell width 56 90 74 73.98 0.82 5.73 7.75 -0.482 2.451
aperture width 23 33 28 28.02 0.28 1.93 9 CO 6. 0.205 1.152
neck length 29 48 39 38.47 0.55 3.84 9.98 -0.288 0.290
neck width 26 42 35 35.33 0.43 3.01 8.52 -0.911 1.837
area of the optical section 4270 9684 6792 6796 134 935 13.75 0.018 2.234
shell width/shell length 0.50 0.66 0.57 0.57 0.00 0.03 4.88 0.381 0.943
aperture width/shell length 0.19 0.28 0.21 0.22 0.00 0.02 7.56 1.200 2.729
neck length/shell length 0.24 0.34 0.30 0.30 0.00 0.02 6.44 -0.048 1.112
neck width/shell length 0.20 0.35 0.27 0.27 0.00 0.02 7.99 0.092 4.818
aperture width/shell width 0.34 0.43 0.38 0.38 0.00 0.02 6.32 0.260 -0.776
neck length/shell width 0.43 0.64 0.53 0.52 0.01 0.04 8.17 -0.013 0.203
neck width/shell width 0.37 0.55 0.48 0.48 0.00 0.03 7.20 -0.386 1.060
neck length/aperture width 1.07 1.66 1.36 1.38 0.02 0.13 9.48 -0.045 -0.215
neck width/aperture width 1.00 1.39 1.27 1.26 0.01 0.07 5.83 -1.032 2.171
neck width/neck length 0.65 1.19 0.93 0.92 0.01 0.09 9.58 0.110 2.473
Abbreviations: Min and Max - minimum and maximum values, M - median, x - arithmetic mean, SE - standard error of the arithmetic mean, SD - standard deviation, CV - coefficient of variation in %, Sk - skewness, Ku - kurtosis.
resulting deviation from the normal Gaussian distribution was minimal. However, negative value for aperture width/shell width ratio was clearly different from zero (-0.776), indicating that the average size group has a lower dispersion. Other variables were found to have positive kurtosis values, indicating a distribution that is sharper than the standard Gaussian distribution. Low positive value (0.203) was observed for neck length/shell width ratio, while a moderate positive value (0.290) was observed for neck length. High positive values (0.943-4.818) were observed for all other variables.
Sphagnum-dwelling population from the Alagovac Lake region
Figure 6 shows scatter plot analysis of the correlation between shell length and shell width, indicating presence of two size classes (small-size and large-size) without intermediate specimens. For the specimen with the pointed shell fundus I measured the following values: shell length 102 ^m, shell width 64 ^m, aperture width 26 ^m, neck length 29 ^m, neck width 26 ^m, and area of the optical section 4281 ^m2. Morphometric characters of 1024 Sphagnum-dwelling specimens from the Alagovac Lake region were measured and the results are given in Table 3. only 15 specimens are included in the small-size class, while the large-size class includes higher number of specimens. Therefore, only the detailed analysis of the large-size class is presented.
Small-size class. Figure 7 shows light micrographs of small-size specimens. Coefficients of variation were moderate for three measured characters (neck length/shell width ratio, neck length/aperture width ratio and neck width/neck length ratio) and ranged from 10.13% to 13.30%; other measured characters had low variability (from 2.82% to 7.76%). For basic characters, the minimal variability was observed for shell length (2.82%), while the maximal variation coefficient was observed for neck length (7.76%). For ratio characters, the minimal variability was observed for neck width/shell width ratio (5.19%), while the maximal variation coefficient was observed for neck length/aperture width ratio (13.30%).
Large-size class. Figure 8 shows light micrographs of large-size specimens. Coefficients of variation were moderate for five measured characters (neck length, area of the optical section, neck length/shell width ratio, neck length/aperture width ratio and neck width/neck length ratio) and ranged
from 10.23% to 11.38%; other measured parameters were characterized by low variability (from 4.83% to 8.34%). For basic characters, the minimal variability was observed for shell length (5.49%), while the maximal variation coefficient was observed for area of the optical section (10.95%). For ratio characters, the minimal variability was observed for shell width/ shell length ratio (4.83%), while the maximal variation coefficient was observed for neck length/ aperture width ratio (11.38%). The most frequent shell length (121 and 123 ^m) was registered in 62 specimens (Fig. 9A); the most frequent shell width (69 ^m) was registered in 97 specimens (Fig. 9B), and the most frequent aperture width (28 ^m) was registered in 239 specimens (Fig. 9C).
Analysis of the size frequency distribution of the measured specimens indicates that this morphometric group is size-monomorphic. For example, shell length ranged from 101 to 139 ^m. However, 66.80% of all measured specimens had shell length of 116-128 ^m, whereas only 21.01% were smaller than 116 ^m and only 12.19% were larger than 128 ^m. The frequency analysis of the shell width shows similar distribution pattern. Namely, all measured specimens had shell width ranging between 56 and 83 ^m. In this case, 66.11% of all specimens had shell width of 65-73 ^m, whereas only 25.67% were narrower than 65 ^m and only 8.22% were wider than 73 ^m. Figures 9D-F show bag plots analyses of the correlation between shell length, shell width and aperture width.
The negative value of skewness (-0.148) for shell length suggests an asymmetrical distribution with a long tail toward lower values. Moderate positive skewness values (0.265-0.468) were observed for neck width/shell length ratio, aperture width/shell width ratio, and neck width/shell width ratio. High positive values (between 0.580 and 1.056) were observed for neck length, aperture width/shell length ratio, neck length/shell length ratio, neck length/ shell width ratio, and neck length/aperture width ratio. All other variables were characterized by low positive skewness values (0.084-0.222).
Four characters (shell length, shell width, neck width, and area of the optical section) displayed negative kurtosis values, meaning that they were characterized by flatter distribution than a standard Gaussian distribution. Because the negative values obtained for these variables were not clearly different from zero (between -0.002 and -0.187), the resulting deviation from normal Gaussian distribution was minimal. Other variables were found to have positive
Fig. 5. Morphological variability of Padaungiella lageniformis based on 49 specimens from Sargan Mountain (Serbia). Histograms show the size frequency distribution of the shell length (A), shell width (B), and aperture width (C); bag plots show the correlation between shell length and shell width (D), aperture width and shell length (E), and aperture width and shell width (F). Legend for bag plots: depth median ♦, characters on Y axes •, outliers ■.
Table 3. Morphometric characterization of Sphagnum-dwelling population of Padaungiella lageniformis from the Alagovac Lake region (East Herzegovina) based on 1024 specimens (small-size class - 15 specimens, and large-size class - 1009 specimens). Measurements are in jm, except for area of the optical section in jm2.
Characters classes Min Max M x SE SD CV Sk Ku
shell length small 91 100 97 96.6 0.70 2.72 2.82 - -
large 101 139 121 120.99 0.21 6.64 5.49 0.148 0.187
shell width small 53 60 55 55.47 0.58 2.26 4.08 - -
large 56 83 68 67.50 0.14 4.45 6.59 0.118 0.002
aperture width small 21 27 24 24.27 0.42 1.62 6.69 - -
large 23 35 28 27.69 0.05 1.71 6.16 0.220 0.290
neck length small 22 30 27 26.6 0.53 2.06 7.76 - -
large 23 55 34 34.12 0.11 3.58 10.48 0.911 2.685
neck width small 24 29 26 26.7 0.37 1.45 5.43 - -
large 25 38 31 31.16 0.07 2.16 6.95 0.222 0.042
area of the optical section small 3450 4245 3783 3793 46.85 181 4.78 - -
large 4010 7798 5717 5718 19.72 626 10.95 0.125 0.150
shell width/shell length small 0.54 0.63 0.57 0.57 0.01 0.03 5.35 - -
large 0.45 0.67 0.56 0.56 0.00 0.03 4.83 0.139 0.676
aperture width/shell length small 0.21 0.28 0.25 0.25 0.00 0.02 7.51 - -
large 0.18 0.30 0.23 0.23 0.00 0.01 6.13 0.580 1.622
neck length/shell length small 0.23 0.31 0.27 0.28 0.01 0.02 7.46 - -
large 0.21 0.40 0.28 0.28 0.00 0.02 8.34 0.670 1.707
neck width/shell length small 0.24 0.30 0.28 0.28 0.00 0.02 6.60 - -
large 0.20 0.32 0.26 0.26 0.00 0.01 5.79 0.411 1.114
aperture width/shell width small 0.38 0.49 0.43 0.44 0.01 0.03 5.86 - -
large 0.35 0.51 0.41 0.41 0.00 0.02 5.70 0.265 0.220
neck length/shell width small 0.36 0.56 0.49 0.48 0.01 0.05 10.13 - -
large 0.35 0.80 0.50 0.51 0.00 0.05 10.78 1.056 3.146
neck width/shell width small 0.43 0.53 0.48 0.48 0.01 0.02 5.19 - -
large 0.39 0.57 0.46 0.46 0.00 0.02 5.15 0.468 0.855
neck length/ aperture width small 0.81 1.43 1.08 1.10 0.04 0.15 13.30 - -
large 0.79 2.12 1.22 1.24 0.00 0.14 11.38 1.043 3.879
Table 3. Continuation.
Characters classes Min Max M x SE SD CV Sk Ku
neck width/aperture width small 0.96 1.19 1.12 1.10 0.02 0.06 5.29 - -
large 0.87 1.32 1.12 1.13 0.00 0.06 5.62 0.084 0.083
neck width/neck length small 0.83 1.32 1.00 1.01 0.03 0.12 12.33 - -
large 0.54 1.38 0.91 0.92 0.00 0.09 10.23 0.125 1.726
Abbreviations: Min and Max - minimum and maximum values, M - median, x - arithmetic mean, SE - standard error of the arithmetic mean, SD - standard deviation, CV - coefficient of variation in %, Sk - skewness, Ku - kurtosis.
kurtosis values, indicating a distribution which is sharper than a standard Gaussian distribution. Low positive values were observed for neck width/ aperture width (0.083) and aperture width/shell width (0.220). A moderate positive value (0.290) was observed for aperture width. All other parameters were characterized by high positive skewness values (0.676-3.879).
Moss-dwelling population from the Alagovac Lake region
Figure 10 shows scatter plot analysis of the correlation between shell length and shell width, indicating that this population is size-monomor-phic. Morphological variability of this population
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Fig. 6. Scatter plot shows the correlation between shell length and shell width of 1024 specimens of Padaungiella lageniformis from a Sphagnum-dwelling population near Alagovac Lake, East Herzegovina. Ellipse represents 98% confidence interval.
is illustrated in Figure 11. Morphometric characters of 403 specimens were measured and the results are given in Table 4. Coefficients of variation were moderate for four measured characters (area of the optical section, neck length/shell width ratio, neck length/aperture width ratio and neck width/ neck length ratio) and ranged from 10.33% to 12.72%; other measured characters were described by low variability (from 5.23% to 9.54%). For basic characters, the minimal variability was observed for shell length (5.83%), while the maximal variation coefficient was observed for area of the optical section (12.72%). For ratio characters, the minimal variability was observed for shell width/shell length ratio (5.23%), while the maximal variation coefficient was observed for neck length/aperture width ratio (11.20%). The most frequent shell length (110 ^m) was registered in 32 specimens (Fig. 12A); the most frequent shell width (58 ^m) was registered in 39 specimens (Fig. 12B), and the most frequent aperture width (24 ^m) was registered in 101 specimen (Fig. 12C).
Analysis of the size frequency distribution of shell length, shell width and aperture width indicates that this population is size-monomorphic. Shell length ranged from 93 to 128 ^m. However, 64.27% of all measured specimens had shell length of 105-115, whereas only 19.60% were smaller than 105 ^m and only 16.13% were larger than 115 ^m. The frequency analysis of the shell width shows similar distribution pattern. Namely, all measured specimens had shell width ranging between 47 and 73 ^m. In this case, 68.24% ofall specimens had shell width of55-63 ^m, whereas only 13.65% were narrower than 55 ^m and only 18.11% were wider than 63 ^m. Figures 12D-F show bag plots analyses of the correlation between shell length, shell width and aperture width.
Fig. 7. Light micrographs of small specimens of Padaungiella lageniformis from a Sphagnum-dwelling population near Alagovac Lake (East Herzegovina) — broad lateral view of different specimens showing general shell shape and outline. Scale bars: 20 ^m.
Table 4. Morphometric characterization of moss-dwelling population of Padaungiella lageniformis from the Alagovac Lake region (East Herzegovina) based on 403 specimens (measurements in |jm, except for area of the optical section in jm2)
Characters Min Max M x SE SD CV Sk Ku
shell length 93 128 110 109.58 0.32 6.38 5.83 0.132 0.002
shell width 47 73 58 59.21 0.24 4.73 7.98 0.537 -0.032
aperture width 21 34 25 25.10 0.09 1.76 7.02 0.811 1.985
neck length 23 42 32 32.09 0.15 3.06 9.54 0.253 -0.122
neck width 24 38 28 28.39 0.10 2.10 7.40 0.668 1.207
area of the optical section 3214 6592 4542 4594 29.12 585 12.72 0.693 0.533
shell width/shell length 0.45 0.63 0.54 0.54 0.00 0.03 5.23 0.295 0.002
aperture width/shell length 0.20 0.32 0.23 0.23 0.00 0.01 6.24 0.972 4.325
neck length/shell length 0.24 0.37 0.29 0.29 0.00 0.02 8.30 0.229 -0.172
neck width/shell length 0.22 0.33 0.26 0.26 0.00 0.02 5.99 0.639 1.290
aperture width/shell width 0.34 0.58 0.42 0.43 0.00 0.03 6.49 0.580 1.937
neck length/shell width 0.41 0.71 0.54 0.54 0.00 0.06 10.46 0.232 -0.177
neck width/shell width 0.41 0.58 0.48 0.48 0.00 0.03 6.27 0.522 0.492
neck length/ aperture width 0.85 1.68 1.27 1.28 0.01 0.144 11.20 0.349 0.124
neck width/aperture width 0.91 1.36 1.13 1.13 0.00 0.06 5.69 0.170 0.946
neck width/neck length 0.67 1.19 0.90 0.89 0.00 0.09 10.33 0.199 -0.204
Abbreviations: Min and Max - minimum and maximum values, M - median, x - arithmetic mean, SE - standard error of the arithmetic mean, SD - standard deviation, CV - coefficient of variation in %, Sk - skewness, Ku - kurtosis.
Fig. 8. Light micrographs of large specimens of Padaungiella lageniformis from a Sphagnum-dwelling population near Alagovac Lake (East Herzegovina) — broad lateral view of different specimens showing general shell shape and outline. A — typical specimens; B — specimens with elongated neck. Scale bars: 20 ^m.
The negative values of skewness were not observed for any characters. Namely, all measured variables were characterized by an asymmetric distribution with a long tail toward higher values. The asymmetry of shell length, neck length/shell length ratio, neck length/shell width ratio, neck width/aperture width ratio, and neck width/neck
length ratio was low, with a skewness values between 0.132 and 0.232. Moderate positive skewness (0.253-0.349) was observed for neck length, shell width/shell length ratio, and neck length/aperture width ratio. All other variables were characterized by high positive skewness (between 0.522 and 0.972).
Five characters (shell width, neck length, neck
Fig. 9. Morphological variability of 1009 Sphagnum-dwelling large specimens of Padaungiella lageniformis from the Alagovac Lake region (East Herzegovina). Histograms show the size frequency distribution of the shell length (A), shell width (B), and aperture width (C); bag plots show the correlation between shell length and shell width (D), aperture width and shell length (E), and aperture width and shell width (F). Legend for bag plots: depth median ♦, characters on Y axes •, outliers ■.
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Fig. 10. Scatter plot shows the correlation between shell length and shell width of 403 specimens of Padaungiella lageniformis from a moss-dwelling population near Alagovac Lake, East Herzegovina. Ellipse represents 90% confidence interval.
length/shell length ratio, neck length/shell width ratio, and neck width/neck length ratio) displayed negative kurtosis values, meaning that they were characterized by flatter distribution than a standard Gaussian distribution. Because the negative values obtained for these characters were not clearly different from zero (between -0.032 and -0.204), the resulting deviation from normal Gaussian distribution was minimal. Other variables were found to have positive kurtosis values, indicating a distribution which is sharper than a standard Gaussian distribution. Low positive values (between 0.002 and 0.124) were observed for shell length, shell width/shell length ratio, and neck length/aperture width ratio. A moderate positive value (0.492) was observed for neck width/shell width ratio. All other variables were characterized by high positive kurtosis values (between 0.533 and 4.325).
Discussion
There are a number of Quadrulella species that differ from the tear-shaped morphology of Q. symmetrica complex. These taxa are characterized by shell shapes that are similar to some species from the other genera: Q. vas and Q. constricta (as Apodera vas), Q. lageniformis (as Padaungiella lageniformis), and Q. tubulata (as P. tubulata). Kosakyan et al. (2016) noted: "These 'mirror' species could either be a result of convergent evolution or represent cases
of the 'classical' hyalosphenids (A. vas, Padaungiella ssp.) that live in environments where euglyphids are rare but Quadrulella are abundant enough to provide material for building their shells. We suggest that at this point these Quadrulella species must be treated as incertae sedis, and their sequencing will certainly illuminate the conundrum of the evolution of square-shaped plates" (Kosakyan et al., 2016, p. 617).
In the population of P. lageniformis from Sargan Mountain (Serbia) analyzed in the present study I found several specimens completely covered by square plates of Quadrulella members. Namely, this population lives in the environment where euglyphids are rare but Q. symmetrica s.l. and Q. longicollis are abundant. I think that Q. lageniformis and P. lageniformis are different species with square plates originated by different ways — Q. lageniformis possess self-secreted plates, while P. lageniformis possess predated or collected plates. Van Oye (1949) reported clearly different morphometric data and shape of shell plates for these two species from the same locality. Namely, he noted smaller dimensions for P. lageniformis (shell length 107—156 ^m, shell width 62—80 ^m) than for Q. lageniformis (shell length 170-192 ^m, shell width 85-115 ^m). If Q. lageniformis possesses predated or collected square shell plates, why then the typical P. lageniformis from the same environment do not have square plates? However, without the detailed observations of Q. lageniformis based on material from the type population (or another population from Indonesia) all explanations are speculative.
Taxonomy at the species level within the genus Padaungiella is predominantly based on morphometric data. Comparative morphometric data of P. lageniformis and closely related taxa according to different authors are presented in Table 5.
Heinis (1914) described Nebela lageniformis var. cordiformis from Sphagnum mosses collected in the Páramo de Cruz Verde, eastern branch of the Colombian Andes (South America). Jung (1942b) concluded that this taxon is a separate species and made a new taxonomic combination: Nebela cordiformis. This taxon is closely related to P. lageniformis but possesses the pointed end of the shell. Heinis (1914) noted only values for shell length: 128-135 ^m. Van Oye (1949) reported two specimens from Indonesia and noted similar values for shell length (132-140 ^m). Because this
Fig. 11. Light micrographs of Padaungiella lageniformis specimens from a moss-dwelling population near Alagovac Lake (East Herzegovina) — broad lateral view of different specimens showing general shell shape and outline. A — typical specimens; B — specimens long up to 100 ^m. Scale bars: 20 ^m.
taxon is not abundant in any population, detailed morphometric data are not available. Kosakyan et al. (2012) did not mention this species in the list of Padaungiella members. The specimen with the pointed shell fundus observed in the present study is very similar to the specimens described
from colombia, but have smaller shell length. i think that it is a mutant specimen because i have found only one specimen with the pointed shell fundus. Unfortunately, Heinis (1914) did not report the number of the observed specimens. Further molecular and morphometric studies are needed to
Table 5. Comparative morphometric data (minimum-maximum) of Padaungiella lageniformis and closely related taxa according to different authors (all measurements in |jm)
Species Shell length Shell width Aperture width Neck length References
P. lageniformis 125-130 70-82 28-32 - Penard, 1890
100-153 53-93 - 33-40 Hoogenraad and de Groot, 1940
103-113 50-73 - 33-50 Hoogenraad and de Groot, 1940
110-130 57-70 - - Hoogenraad and de Groot, 1940
103-123 51-80 - - Hoogenraad and de Groot, 1940
107-143 53-70 - - Hoogenraad and de Groot, 1940
117-130 60-70 - 40-50 Hoogenraad and de Groot, 1940
119-131 68-85 28-32 40 Jung, 1942a, 1942b
107-156 62-80 25-39 30-46 van Oye, 1949
160 85 35 50 Gauthier-Lièvre, 1953
98-120 50-69 19-25 - Ogden, 1984
125-152 62-78 21-23 - Chung and Choi, 1995
125-138 63-75 23-28 53-59 Chattopadhyay and Das, 2003
91-127 51-73 21-30 23-39 Luketa, 2015
101-153 56-90 23-33 29-48 This study
91-139 53-83 21-35 22-55 This study
93-128 47-73 21-34 23-42 This study
P. nebeloides 118-140 35-45 17-20 - Gauthier-Lièvre and Thomas, 1958
113-126 45-53 19-23 35-45 Meisterfeld, 1979
113-140 43-54 17-21 33-45 Todorov et al., 2010
115-125 44-54 18-20 33-38 Todorov et al., 2010
P. wailesi 75-100 50-55 25-30 - Deflandre, 1936
91-105 50-58 22-28 30-34 Jung, 1942a, 1942b
75-85 53-58 17-22 25-31 Chattopadhyay and Das, 2003
P. wetekampi 149-159 60-70 26-33 63-68 Jung, 1942a, 1942b
Nebela cordiformis 128-135 - - - Heinis, 1914
132-140 87-95 - 43-50 van Oye, 1949
clarify taxonomic status of this taxon.
Jung (1942a) described Schaudinnia wetekampi as a pyriform species with a very long pronounced neck. He noted the following measurements: shell length 149-159 ^m, shell width 60-70 ^m, shell depth 30-47 ^m, aperture width 26-33 ^m, neck length 63-68 ^m, and neck width 25 ^m. Jung (1942a) believed that Playfair (1917) observed S. wetekampi instead of Nebela militaris var. tubulata. However, the specimens described by Playfair (1917) have smaller dimentions: shell length 60-64 ^m, shell width 26-30 ^m, and aperture width 9-14
^m. Kosakyan et al. (2012) included S. wetekampi in the list of Padaungiella members because it is very similar to the type species — P. lageniformis. Namely, key difference between these two species is length of neck. Chattopadhyay and Das (2003) described specimens of P. lageniformis with very long neck (53—59 ^m) based on material from India. In the present study, I also observed specimens with long neck (up to 55 ^m). However, intermediate forms between shells with short neck and shells with long neck were also observed. Unfortunately, detailed morphometric data for P. wetekampi are
Fig. 12. Morphological variability of Padaungiella lageniformis specimens from moss-dwelling population near Alagovac Lake (East Herzegovina) based on 403 specimens. Histograms show the size frequency distribution of the shell length (A), shell width (B), and aperture width (C); bag plots show the correlation between shell length and shell width (D), aperture width and shell length (E), and aperture width and shell width (F). Legend for bag plots: depth median ♦, characters on Y axes •, outliers ■.
not available. Further studies on morphological variability of P. wetekampi are needed to clarify taxonomic status of this species.
Gauthier-Lièvre and Thomas (1958) described Difflugia nebeloides from Africa. Todorov et al. (2010) based on two populations from Bulgaria and Austria reported morphological, morphometrical and ecological characteristics of D. nebeloides and included this species into the genus Nebela. However, Lara and Todorov (in Kosakyan et al., 2012) based on molecular data included this species into the genus Padaungiella. The shell of P. nebeloides is circular in transverse section, while P. lageniformis have laterally compressed shell. Todorov et al. (2010) noted that values of shell width/shell length ratio ranged between 0.34 and 0.46. Van Oye (1949) reported seven specimens of P. lageniformis characterized by shell width/shell length ratio values between 0.51 and 0.58. Luketa (2015) calculated values of shell width/shell length ratio for P. lageniformis based on specimens from the Vlasina Lake region (Serbia) and noted that values of this ratio ranged from 0.46 to 0.63. In addition, all specimens of P. lageniformis analyzed in the present study have similar ratio of shell width and shell length (0.45—0.67). It is possible to conclude that shell width/shell length ratio is a very important taxonomic character for distinguishing these two species. Unfortunately, Todorov et al. (2010) did not calculate ratio values for the other characters.
Polymorphism is simultaneous presence of two or more phenotypes in a population or interrupted diversity of forms on the common genetic base. There are two types of this phenomenon: continuous and discontinuous polymorphism. In the cases of continuous polymorphism, it is not possible to distinguish clearly defined size classes. This type of polymorphism is relatively common among testate amoebae (Schonborn and Peschke, 1988; Schonborn, 1992; Golemansky and Todorov, 2006; Todorov, 2010). However, so far size discontinuous polymorphism was registered only in three cases among testate amoebae: Centropyxis plagiostoma (Foissner and Korganova, 1995), Apodera vas (Zapata and Fernández, 2008), and Trinema penardi (Luketa, 2016). In the present study, the Sphagnum-dwelling population of Padaungiella lageniformis near Alagovac Lake demonstrated a new example of size discontinuous polymorphism.
Wailes (1912) described Nebela lageniformis var. minor from the North America and noted that
a small form, which differed from the type in size only, was not uncommon; the individuals observed varied from 85—100 ^ in length. Deflandre (1936) proposed new taxonomic status and name for this taxon: Nebela wailesi. Kosakyan et al. (2012) based on molecular data included this species into the genus Padaungiella. However, Luketa (2015) described size-monomorphic population of P. lageniformis with specimens characterized by shell length ranging between 91 and 127 ^m. Also, moss-dwelling population from the Alagovac Lake region (East Herzegovina) analyzed in this study showed similar values of shell length (93—128 ^m). This population is also size-monomorphic. Meanwhile, Sphagnum-dwelling population from the Alagovac Lake region is size-dimorphic, with two morphometric classes: small-size (91—100 ^m) and large-size (101—139 ^m). Results ofthe present study suggest that P. wailesi is not a taxon but a size-class in some populations of P. lageniformis. For this reason, I suggest synonymizing P. wailesi with P. lageniformis.
Acknowledgments
I am very grateful to Dr. Ivo Karaman and Dr. Lâszlo Barsi (University of Novi Sad, Serbia) for moss sample from Sargan Mountain. Also, I am very grateful to Dr. Lâszlo Barsi for permission to use the Zeiss Axio Imager A1 light microscope.
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Address for correspondence: Stefan Luketa. Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovica 2, 21000 Novi Sad, Serbia; e-mail: [email protected]. ac.rs
