Bull 875 Bull. Iraq nat. Hist. Mus. (2025) 18 (4): 875-898. https://doi.org/10.26842/binhm.7.2025.18.4.0875 ORIGINAL ARTICLE DIVERSITY AND SPATIOTEMPORAL VARIATIONS OF ROTIFERA OF THE SAMARRA DAM, IRAQ Osama S. Majeed Directorate of Baghdad Education Karkh III, Ministry of Education, Baghdad, Iraq E-mail: osamaalways230@gmail.com Received: 13 April 2025, Revised: 2 Oct. 2025, Accepted: 8 Oct. 2025, Published: 20 December 2025 This work is licensed under a Creative Commons Attribution 4.0 International License ABSTRACT This investigation is the first of its kind in this reservoir for more than three decades, it aimed at evaluating the diversity, abundance, and spatiotemporal variations of rotifers in the Samarra dam during 2023. Three distinct sampling stations were selected to ensure a comprehensive coverage of the dam. The first station was located just below the river's entrance to the dam. The second station was situated near the Samarra Barrage, while the third was positioned close to the Tharthar Regulator. Fifty-seven taxa from fourteen families of rotifers were identified, classified into three orders: Ploima, Flosculariaceae, and Bdelloida, under the Eurotatoria class. Most abundant taxa were Synchaeta oblonga Ehrenberg,1832, Rotaria neptunia (Ehreberg,1830), Euchlanis dilatata Ehrenberg, 1832, Polyarthra dolichoptera Idelson,1925, Brachionus calyciflorus Pallas, 1766 (long and short spine), B. urceolaris Müller, 1773, and Keratella cochlearis (Gosse, 1851). Minimum and maximum densities were in winter and spring, respectively. Mean values for richness, evenness and diversity indices were 5.18, 4.75 and 6.37; 0.8, 1.8 and 0.8; 2.2, 1.8 and 2.4 bits/ind. At stations 1, 2 and 3, respectively. Seasonally, the highest and lowest values of evenness and diversity indices were in summer and winter, respectively, while the richness index it was observed in autumn and spring seasons. Also, the highest similarity index value was 68.78% between first and third stations. Whereas the largest difference of species composition observed between second and third stations reached 7.76%. Keywords: Brachionidae, Constancy, Diversity, Lecanidae, Rotifers, Samarra Dam. INTRODUCTION Rotifera, commonly known as wheel organisms, because there is the ciliated ring located on the top of their head (Manickam et al., 2019; José de Paggi et al., 2020). Generally, it is microscopic, and varies between 40-2,000 μm in size, composed of thousands of cells, unsegmented, bilaterally symmetrical, pseudocoelomate animals (Wallace et al., 2015; Manickam et al., 2019; José de Paggi et al., 2020). Segers (2007) states that this group is found in various aquatic systems and classified into three main groups: Monogononta, BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Iraq Natural History Research Center & Museum, University of Baghdad https://jnhm.uobaghdad.edu.iq/index.php/BINHM/Home Copyright © Bulletin of the Iraq Natural History Museum Online ISSN: 2311-9799, Print ISSN: 1017-8678 https://doi.org/10.26842/binhm.7.2025.18.4.0875 https://orcid.org/0000-0003-2417-8869 mailto:osamaalways230@gmail.com https://creativecommons.org/licenses/by/4.0/ https://jnhm.uobaghdad.edu.iq/index.php/BINHM/Home 876 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Bdelloidea and Seisonida. Most rotifers inhabit freshwater, while some can survive in salty waters (Balian et al., 2007; Segers, 2008). These organisms, particularly Rotifera, give a complete visibility of the condition of an aquatic system and serve as bioindicators for pollution and eutrophication (Renuga et al., 2010; Abbas and Talib, 2018; Majeed et al., 2022a; Sharaf et al., 2023). Many regional studies have concentrated on zooplankton in the Tigris River, with particular attention given to rotifers such as those by Sabri et al. (1993), Majeed et al. (2021, 2022 a, b, 2023 a, b) and Abed et al. (2022). For a long time, there have been no zooplankton studies conducted in this section of the river. As a result, this research is the first of its kind in this reservoir in over thirty years, aiming to assess the diversity of rotifers in the water of Samarra Dam. MATERIALS AND METHODS Study area: In the western part of Samarra City, the multipurpose Samarra Dam sits. The main goal of this project is to redirect floodwaters from the Tigris River to the Tharthar Reservoir during flood periods via the Tigris-Al Tharthar Canal. This system is utilized for irrigation, flood management, and power generation. The Züblin company completed the project in 1956. It has 17 control gates that allow 7,000 m3/s of water to flow the Tigris, whereas the Tharthar regulator allows 9,000 m3/s to flow through a canal with 36 gates (Abdulridha and Al Thamiry, 2017). Study area description: The study area was the Samarra Dam located on the Tigris River in Salah Al-Din Province. Samples were taken from February to December 2023 at three selected stations. The first station was located upstream the dam and directly below the river's entrance (34°12'25.8"N 43°50'50.2"E). The second station was located near Samarra Barrage at 34°12'22.8"N 43°51'28.0"E. Whereas, the third station was located near Tharthar Regulator at 34°11'53.4"N latitude and 43°51'04.9"E longitude (Tab. 1, Map 1). Table (1): Coordinates for three selected stations in the Samarra Dam for the period from February to December 2023. Stations GBS Coordination Explanation Latitude lines Longitude lines S 1 34°12'25.8"N 43°50'50.2"E Below the river's entrance S 2 34°12'22.8"N 43°51'28.0"E Near the Samarra Barrage S 3 34°11'53.4"N 43°51'04.9"E Near the Tharthar Regulator 877 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Map (1): Showing locations of studied stations in Samarra Dam. (Source: Ministry of water Resources\ General Authority of Survey, 2023). Sampling Collection: During a complete year 2023, the samples were taken from the littoral zone at < 1 m depth every two months; 45 litres of water were filtered through a funnel- shaped planktonic net with a 55-micron mesh size, with the aid of a graduated pail. After filtration, the retained material in each mesh was washed with filtered river water. Each sample was preserved in 4% formalin (Juday, 1916; Welch, 1948; Rocha et al., 2021). Identification of Rotifers: After the sample had condensed, the Rotifera were identified to the lowest taxonomic unit using a Sedgewick-Rafter counting slide under a compound microscope. The rectangular hollow slide held precisely one milliliter of water sample, measuring 50 mm in length, 20 mm in width, and 1 mm in depth. The density was determined by the formula provided by Baird et al. (2017). Where n is rotifers number. The results were presented as the number of individuals per m3 Identification is based on the revisions by Edmondson (1959), Pontin (1978) and Smith (2001) supplemented by recently published additions (Wallace et al., 2015; José de Paggi et al., 2020). 878 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Following identification keys were used to distinguish and differentiate among the rotifer species based on variations in external morphology, including shape, corona, neck, trunk, spine, foot, and toes. • Variations in shapes: some species have sack-shaped, e.g., Asplanchna priodonta Gosse, 1850, oval-shaped e.g., Lepadella ovalis (Müller, 1786), cylindrical-shaped, e.g., Trichocerca bicristata (Gosse, 1887), bell-shaped, e.g., Synchaeta oblonga Ehrenberg, 1832, and elongated shape, e.g., Rotaria citrina (Ehrenberg, 1838). • Variations of the foot: includes the presence or absence of the foot, the presence or absence of toes, and their structure and length. The foot often extends ventrally from the body. For example, Keratella cochlearis Gosse, 1851 lacks a foot, while Brachionus calyciflorus calyciflorus Pallas, 1776 has a posterior foot with equally sized toes. • Toes variations can include number, length, size, and shape. Usually, a foot possesses two toes, but this number can range from zero to four. For instance, Cephalodella gibba (Ehrenberg, 1830), and Lepadella ovalis (Müller, 1786) each have two long, slender toes. The foot in Trichotria tetractis (Ehrenberg, 1830) is composed of 3 segments, the first segment bearing two dorsal triangular spines. The second segment of the foot is longer than the other two. Toes long, slender, ending in a point. • Variation of the corona: included the presence or absence of cilia, the number of rows of cilia, structure, shape, location, and size. For example, the corona of Collotheca ornate (Ehrenberg, 1832) is modified into a funnel surrounding the mouth. In Testudinella patina (Hermann, 1783), the cilia around the mouth have disappeared, leaving just two small circular bands on the head. In the bdelloids, the upper band splits into two rotating wheels. • Variations in the lorica: include its presence or absence, shape, length, size, and rigidity. For example, in Synchaeta oblonga (Ehrenberg, 1832), the lorica is absent. In Brachionus plicatilis (Müller, 1786), the lorica is spherical in shape. In Brachionus urceolaris (Müller, 1773) the lorica is hard with longitudinal lines. While in Lepadella ovalis (Müller, 1786), the lorica is without striations. • Variations of the spines: included the presence or absence of the spines, number, longevity, and location on the anterior edge or posterior of the lorica. For example, Brachionus angularis Gosse, 1851, lacks any anterior spines, only the median spines are prominent and there is a deep sinus in between them. Keratella cochlearis Gosse, 1851 has six spines along the anterior dorsal margin of the lorica, the median spines being the longest and curved ventrally. Additionally, there are two unequal posterior spines, with the right spine always longer than the left. The genus Brachionus is distinguished by the presence of spines along its anterior border. For example, Brachionus calyciflorus calyciflorus Pallas, 1776 has four broad-based spines, with the medial spines being slightly longer than the lateral ones, along with two posterolateral spines. In contrast, Brachionus forficula Wierzejski, 1891, has four anterior spines varying in length, where the lateral spines are longer than the medial ones. 879 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. It is important to note that the differences among species, such as increased body size, thicker lorica, and the development and elongation of spines as morphological defenses, can effectively protect animals from being captured. This phenomenon is known as hidden defensive morphology in rotifers. For example, Brachionus forficula Wierzejski, 1891 can develop long or short posterior spines in response to predators or environmental conditions (Ge et al., 2012; Yin et al., 2017). Ecological indicators: The following ecological indices have been used to determine Rotifera diversity such as Relative Abundance Index (Ra) (Omori and Ikeda, 1984); Constancy Index (S) (Ishizaka and Labib, 2011); Jaccard similarity index (Jaccard, 1908); Species Evenness Index (J) (Magurran, 2004); Species Richness Index (D) (Margalefe, 1968) and Shannon- Weiner Index (H') for diversity (Shannon and Weaver, 1949). Results are represented in bits per individual, where a bit is defined as a single piece of information. An ecosystem with H' value greater than 2 bits per number has been regarded as medium to high diverse in terms of species (Majeed et al., 2022a; Charlotte and Dronkers, 2025). RESULTS AND DISCUSSION Species composition According to the current investigation, fifty-seven rotifer species belonging to 26 genera and 14 families were identified from three stations in Samarra Dam water as listed below: 36 species in station 1, 49 species in station 2 and 44 species in station 3 (Tab. 2). Findings revealed that the genus Brachionus has 11 species including Brachionus angularis Gosse, 1851, B. bidentatus Anderson, 1889, B. calyciflorus calyciflorus Pallas, 1776, B. calyciflorus f. amphiceros Ehrenberg, 1838 (long spin), B. calyciflorus f. amphiceros Ehrenberg, 1838 (short spin), B. forficula Wierzejski, 1891, B. havanaensis Rousselet, 1913, B. quadridentatus Hermann,1783, B. quadridentatus Hermann,1783 (long spin), B. quadridentatus Hermann,1783 (short spin) and B. urceolaris Müller, 1773. Lecane has 11 species including Lecane elasma Harring & Myers, 1926, L. luna (Müller, 1776), L. tenuiseta (Harring, 1914), L. bulla (Gosse, 1851), L. closterocerca (Schmarda, 1859), L. hamata (Stokes, 1896), L. quadridentata (Ehrenberg, 1832), L. lunaris (Ehrenberg, 1832), L. stenroosi (Meissner, 1908), L. stenroosi (Meissner, 1908), L. stenroosi (Meissner, 1908), L. stenroosi (Meissner, 1908), L. thalera (Harring & Myers, 1926) and L. thienemanni (Hauer, 1938). Keratella has 5 species including Keratella cochlearis (Gosse, 1851), K. quadrata (Müller, 1786) (long spin), K. quadrata (Müller, 1786) (short spin), K. tropica (Apstein, 1907) and K. valga (Ehrenberg, 1834). Trichocerca has 3 species including Trichocerca bicristata (Gosse, 1887), T. rousseleti (Voigt, 1902) and T. similis (Wierzejski, 1893). Asplanchna has 2 species including Asplanchna brightwellii Gosse, 1850 and A. priodonta Gosse, 1850. Lepadella has 2 species including Lepadella ovalis (Müller, 1786) and L. salpina Ehrenberg, 1834. Platyias has 2 species including Platyias patulus (Müller, 1786) and P. quadricornis (Ehrenberg, 1832). Polyarthra has 2 species including Polyarthra dolichoptera Idelson,1925 and P. vulgaris Carlin, 1943. Rotaria has 2 species including Rotaria citrina (Ehrenberg, 1838) and R. neptunia (Ehreberg,1830). Synchaeta has 2 species 880 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations including Synchaeta oblonga Ehrenberg,1832 and S. pectinata Ehrenberg, 1832. Whereas other identified genera had only one species. Among the various families of rotiferians, Brachionidae and Lecanidae have the highest number of species, with 20 and 11 identified taxa respectively. The dominance of these two families is likely due to the remarkable adaptability of their organisms to different limnological conditions and available food sources (Liu et al., 2023; Kuczyńska-Kippen et al., 2025). Species from these families are typically predominant in different aquatic systems (Kuczyńska-Kippen and Ejsmont-Karabin, 2020; Phan et al., 2021; Bozkurt, 2024). Density and abundance ratio Diagram (1) shows the total density of rotifers. In the first station, values of rotifer densities varied between 855.2 Ind./m3 and 3530 Ind./m3 in December and April, respectively. In the second station, the values varied between 826.4 and 159198.18 Ind./m3 in August and February, respectively. In the third station, the minimum value was 621.7 Ind./m3 in December while the maximum value was 4110 Ind./m3 in October. As well, the total rotifera density was 10940.26, 310934 and 14010.8 Ind./m3 in stations 1, 2 and 3, respectively (Tab. 3). Rotifer density showed seasonal variations, with maximum densities were noticed in spring, whereas minimum densities were in winter (Diag. 1), similar findings obtained by Majeed et al. (2022a) related to suitable environmental conditions in the Tigris River, such as temperature and nutrient availability, which play an important role in growing microalgae as an essential feeding resource. This fact supported by Salman (2024) who showed that rotifer density increased in the spring season. While the density values decreased in winter, this may be ascribed to decreasing water temperatures and increasing turbidity and suspended matter, a situation which affected the density of rotifers. The findings of Abdulwahab and Rabee (2015) and Salman (2024) supported this fact. In India, the same results were reported by Kiran et al. (2007) who found that rotifer density decreased in the rainy season and increased in the summer season in fish pond, Karnataka. Spatially, the second station recorded the highest density at 159198.18 Ind./m3, while the third station had the lowest value at 621.7 Ind./m3 (Diag. 1). This may be attributed to the changes in environmental factors at the two sites, such as dissolved oxygen, water temperature, nutrients and presence of microalgae, these findings were proved by Czerniawski and Sługocki (2017), Bolawa et al. (2018) and Majeed et al. (2022a). The most abundant taxa in the Samarra Dam were S. oblonga, R. neptunia, E dilatata, P. dolicoptera, Brachionus spp., and Keratella spp. (Tab. 2, Diag. 2). Higher species abundance in station 1 was S. oblonga 20%, E. dilatata 17%, R. neptunia 15%, P. dolichoptera, B. urceolaris 10%, K. cochlearis 9%, Notholca squamula 3% and Pompholyx sulcata 3%. In station 2, S. oblonga, 59%, B. calyciflorus amphecerus (long spin) 13%, B. calyciflorus amphecerus (short spin) 8%, P. dolichoptera, 6% and B. angularis 3%. 881 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Whereas, in station 3, S. oblonga, R. neptunia, E. dilatata, K. cochlearis, A. fissa, B. angularis B. forficula and B. urceolaris were recorded 28, 15, 8, 7, 4, 4, 3 and 3%, respectively (Diag. 2). Similar findings were reported in the Tigris River (Sabri et al., 1993; Majeed et al., 2022a). As well, this is a common feature observed in many various Iraqi reservoirs (Hammadi et al., 2015; Al-Ameen et al., 2019; Al-Bahathy and Nashaat, 2021; Salman, 2024; Majeed and Nashaat, 2025). Diagram (1): Total Rotifera density in the Samarra Dam during 2023. 882 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Diagram (2): The most dominant Rotifera in the Samarra Dam during 2023. 883 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Table (2): Distribution, abundance and consistency of Rotifera species in the three stations of the Samarra Dam during 2023. Subclass: Monogononta Order: Ploima Abundance Constancy Family Taxa S1 S2 S3 S1 S2 S3 Asplanchnidae Asplanchna brightwellii Gosse, 1850 - R - - Ac - A. priodonta Gosse, 1850 R R R C C C Dicranophoridae Aspelta bidentata Wulfert, 1961 R R R Ac A A Brachionidae Anuraeopsis fissa Gosse, 1851 R R R C AC C Brachionus angularis Gosse, 1851 R R R C Ac C B. bidentatus Anderson, 1889 R - R A - Ac B. calyciflorus calyciflorus Pallas, 1776 R R R C Ac Ac B. calyciflorus f. amphiceros Ehrenberg, 1838 (long spin form) R La R Ac Ac A B. calyciflorus f. amphiceros Ehrenberg, 1838 (short spin form) - R R - A C B. forficula Wierzejski, 1891 R R R C A C B. havanaensis Rousselet, 1913 - - R - - A B. quadridentatus Hermann,1783 - - R - - Ac B. quadridentatus Hermann,1783 (long spin form) R R R C Ac Ac B. quadridentatus Hermann,1783 (short spin form) - R R - Ac C B. urceolaris Müller, 1773 A R R C Ac C Keratella cochlearis (Gosse, 1851) A R R C C C K. quadrata (Müller, 1786) (long spin form) R R - A Ac - 884 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations K. quadrata (Müller, 1786) (short spin form) R R R Ac Ac Ac K. tropica (Apstein, 1907) R R R Ac Ac A K. valga (Ehrenberg, 1834) R R R C C C Notholca squamula (Müller, 1786) La R R C A A Platyias patulus (Müller, 1786) R R - A Ac - P. quadricornis (Ehrenberg, 1832) - R - - A - Euchlanidae Dipleuchlanis propalula (Gosse, 1886) R R - Ac A - Euchlanis dilatata Ehrenberg, 1832 D R R C C C Manfredium eudactylotum (Gosse, 1886) - - R - - A Lecanidae Lecane elasma Harring & Myers, 1926 - R R - A C L. luna (Müller, 1776) La R R C C C L. tenuiseta (Harring, 1914) - - R - - Ac L. bulla (Gosse, 1851) La R R C C C L. closterocerca (Schmarda, 1859) R R - A A - L. hamata (Stokes, 1896) - R R - A Ac L. quadridentata (Ehrenberg, 1832) - R R - A Ac L. lunaris (Ehrenberg, 1832) - R - - A - L. stenroosi (Meissner, 1908) R - R Ac - Ac L. thalera (Harring & Myers, 1926) R R R A Ac Ac L. thienemanni (Hauer, 1938) - - - - Ac - Lepadellidae Colurella adriatica Ehrenberg, 1831 R R R C C Ac Lepadella ovalis (Müller, 1786) R R R Ac Ac A L. salpina - R R - Ac A 885 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Ehrenberg, 1834 Mytilinidae Mytilina nucronata (Müller, 1773) R R - Ac A - Notommatidae Cephalodella gibba (Ehrenberg, 1830) R R R C C C Synchaetidae Polyarthra dolichoptera Idelson,1925 R R R Ac C C P. vulgaris Carlin, 1943 - R - - Ac - Synchaeta oblonga Ehrenberg,1832 D A La C C C S. pectinata Ehrenberg, 1832 R R - A A - Trichocercidae Macrochaetus subquadratus Perty, 1850 - R - - A - Trichocerca bicristata (Gosse, 1887) R R R A C Ac T. rousseleti (Voigt, 1902) R R - A A - T. similis (Wierzejski, 1893) - R R - Ac - Trichotriidae Trichotria tetractis (Ehrenberg, 1830) R R R Ac C C Order: Flosculariaceae Testudinellidae Pompholyx sulcata Hudson, 1885 La R R Ac A Ac Testudinella patina (Hermann, 1783) - R R - A Ac Hexarthridae Hexarethra mera (Hudson, 1871) - R R - A Ac Subclass: Bdelloidea Order: Bdelloida Philodinidae Macrotrachela quadricornifera Milne, 1886 - R R - A Ac Rotaria citrina (Ehrenberg, 1838) - - R - - Ac R. neptunia (Ehreberg,1830) D R La C C C [D: dominant > 70%; A: abundant 40-70 %; La: less abundant 10-39 %; R: rare < 10 %. For constancy index; C: constant > 50%; Ac: accessory 26-50%; A: accidental 1-25%]. 886 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Ecological indicators Species richness of planktonic rotifers: Diagram (3) depicts the values of the Rotiferian richness index. At the first station, Richness values varied between 3.74 in June and 6.15 in August. At the second station, the value ranged from 1.37 in August and 8.027 in April, whereas at the third station the minimum values were 4.23 in February and the maximum values were 8.038 in April. As well, the average values 5.18, 4.75 and 6.37 were recorded in stations 1, 2 and 3, respectively. Spatially, the maximum value recorded in the third station was 8.038 and the minimum value recorded in the first station was 1.37 (Diag. 3). This could be linked to the variations in environmental factors between the two habitats in the impoundment. This view was proved by Majeed et al. (2022a) who showed that differences in richness values between the Tigris and Tharthar water. Seasonally, the maximum and minimum values of the richness index were during the spring and autumn seasons, respectively (Diag. 3). Increasing richness values in spring season may be related to an increase of phytoplankton in this season. This view was supported by Rasheed et al. (2016) who indicated that higher richness index values in spring would correlate with increased phytoplankton density in the Al-Shamyiah River. Whereas, the lowest value was in autumn season which may be linked to the decreasing in phytoplankton density. This fact was proved by Abed and Nashaat (2018) who showed that decreasing in richness values due to decreasing in phytoplankton density, in Dejiala River. In this respect, Phan et al. (2021) found that rotifera richness index was significantly affected by environmental factors especially temperature, turbidity, pH and trophic level in Da Nang Lakes. 887 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Diagram (3): Monthly fluctuations of D Index for Rotifera at three stations of the Samarra Dam during 2023. Species evenness of planktonic rotifers: At the first station, the evenness values varied between 0.67 in February and 0.84 in December. Whereas in the second station, the least and highest values were 0.33 and 2.64 in February and April, respectively. In the third station the values fluctuated between 0.63 in October and 0.93 in December (Diag. 4). As well, the mean values of the evenness index were 0.8, 1.8 and 0.8 in stations 1, 2 and 3, respectively. All values being greater than 0.5, indicates an unbalanced distribution of Rotifera species (Pielou, 1977; Magurran, 2004). This may be related to the various factors affecting the species evenness such as richness index and sampling size (Faith and Du, 2018). Seasonal variations, showed that the values increased in spring and summer and decreased in winter (Diag. 4). This may be linked to the favorable environmental conditions such as water temperatures, nutrients and chlorophyll availability which consequently support phytoplankton abundance which considered a good food supporting rotifera (Shaker et al., 2019; Lu et al., 2021). These results are consistent with Majeed et al. (2022a) who also proved that Rotiferian evenness index in Tigris water increased in spring and summer and decreased in winter. S1 S2 S3 0 1 2 3 4 5 6 7 8 Stations D I n d e x o f R o ti fe r a Months S1 S2 S3 888 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Spatial variations, the largest values of evenness index were recorded in the second station while the lowest values were in stations 1 and 3 (Diag. 4). This might be caused by variations in the physical, chemical, and hydrological factors among different stations (Kamboj and Kamboj, 2020). S1 S2 S30 1 2 3 Stations E I n d ex o f R o ti fe ra Months S1 S2 S3 Diagram (4): Monthly fluctuations of the Evenness index at three stations of the Samarra Dam during 2023. Diversity index of planktonic rotifers: In the first site, the values of the Shannon-Weiner diversity index ranged from 1.81 bits/ind. in June to 2.73 in August bits/ind. Whereas in the second station, the values varied from 0.33 bits/ind. in February to 2.64 bits/ind. in April. In the third station, the values fluctuated between 1.79 and 2.81 bits/ind. in February and August, respectively (Diag. 5). As well, the mean values of the diversity index were 2.2, 1.8 and 2.4 bits/ind. in stations 1, 2 and 3, respectively (Tab. 3). According to Charlotte and Dronkers (2025) rotifera diversity in the Samarra Dam occurred within good to very good class. Seasonal variations show that the highest and lowest values of this index fluctuated between summer and winter, respectively (Diag. 5). This may be linked to higher temperature, sunlight and Chlorophyll-a availability, all of which are crucial for supporting phytoplankton as a food source for zooplankton (Sharmila-Sree and Shameem, 2017). In winter, the values of this index decreased due to increased turbidity and suspended matter, which negatively 889 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. impacts the diversity of rotifers, as noted by Abdulwahab and Rabee (2015) and Majeed et al. (2022a). For spatial variation, the highest value was in the third station and recorded 2.81. Whereas, the lowest value was in the second station recorded 0.33 (Diag. 5). This could be attributed to the heterogeneity among habitats (Majeed et al., 2022a). In this respect, Phan et al. (2021) mentioned that the high value of rotifera diversity in Da Nang Lakes related to high levels of temperature, turbidity and trophic state. S1 S2 S30 1 2 3 4 Stations H In d e x o f R o ti fe ra Months S1 S2 S3 Diagram (5): Monthly variations of the diversity index at three stations of the Samarra Dam during 2023. 890 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations Table (3): The average values of species richness, evenness and diversity indices along with total densities of rotifers. Index Stations 1 2 3 D 5.18 4.75 6.37 J 0.76 1.78 0.78 H' 2.2 1.8 2.4 Total densities 10940.26 310934 14010.8 Jaccard's similarity index: The largest similarity value observed between the first and third stations was 68.78% (Diag. 6). The similarities between the two stations can be attributed to the fact that both are influenced by the same hydrodynamic conditions and limnological factors. Additionally, they share the same physicochemical characteristics, including water sources, temperature, salinity, dissolved oxygen levels and pH. This result agrees with several Iraqi studies; Majeed et al. (2022a) recorded high similarity index values for rotifera among various places in the Tigris River, attributing that to the suitable environmental conditions. In the Euphrates River, Al-Bahathy and Nashaat (2021) recorded similar results between downstream and upstream of the Hindiya Dam, with the highest value reached 76.27 for Rotifera. In contrast, the lowest value of this index was between the second and the third stations reached 7.76% (Diag. 6). This may be related to the differences between two distinct habitats, including limnological factors and hydrodynamic conditions. Additionally, fluctuations in water currents have a mechanical advective effect on rotifer populations. This view was supported by Hung et al. (2021), who demonstrated that variation in species composition of the rotifera community in different water bodies was influenced by variations of physicochemical factors. A significant inverse relationship between current velocity and zooplankton abundance has been found 891 BULLETIN OF THE IRAQ NATURAL HISTORY MUSEUM Majeed, O. S. Diagram (6): Shows the values of Jaccard's similarity index among the three stations of the Samarra Dam during 2023. Constancy index (S): Table (2) depicts the constant species in three stations in the dam. In station 1 we recorded 17 species. Whereas, in the second and third stations 2 and 3 were 13 and 17 species, respectively. According to the constancy index, the species A. priodonta, A. fissa, B. angularis, B. calyciflorus calyciflorus B. forficula, B. quadridentatus, (long spin), B. urceolaris, K. cochlearis, K. valga, N. squamula, C. gibba, C. adriatica, E. dilatate, L. luna, M. bulla, R. neptunia, and S. oblonga were the most constant species in the first station. Whereas in the second station, the most constant species were A. priodonta, K. cochlearis, K. valga, C. gibba, C. adriatica, E. dilatata, L. luna, M. bulla, R. neptunia, P. dolichoptera, S. oblonga, T. tetractys and T. bicristata. In station 3, A. priodonta, A. fissa. B. angularis, B. calyciflorus amphecerus (short spin), B. forficula, B. quadridentatus (short spin), B. urceolaris, K. cochlearis, K. valga, E. dilatata, C. gibba, L. luna, L. elasma M. bulla, R. neptunia, P. dolichoptera, S. oblonga, and T. tetractys. The results we obtained are consistent with other earlier studies conducted on the Tigris River. Majeed et al. (2022a) observed that B. angularis, E. dilatata, K. valga, K. cochlearis, R. neptunia, P. dolichoptera and S. oblonga were the largest constant rotifers in Tigris water. Al-Azzawii (2015) showed that B. angularis and B. urceolaris were constant species in the Tigris River. Also, Al-Bahathy and Nashaat (2021) reported that E. dilatata constant up and downstream the Hindiya Dam. Based on the aforementioned, Lair (2006) explained that Brachionus sp. can grow at a high current velocity of about 20 cm/s. Also, Jaturapruek (2016) pointed out that R. neptunia is tolerant to a wide range of environmental conditions, and thus it dwells in many freshwater habitats like ponds, lakes and rivers. Glime (2017) reported that E. dilatata is a cosmopolitan 892 Bull. Iraq nat. Hist. Mus. 18 (4): 875-898. Diversity and spatiotemporal variations species able to tolerate a wide range of pH and temperature and so it is present in both freshwater and brackish water. In this respect Dang et al. (2015) reported that L. bulla can survive in widely freshwater aquatic systems like rivers, lakes and ponds. CONCLUSIONS We identified 57 species, belonging to 16 families in this study, the predominant species A. priodonta, A. bidentate, A. fissa, B. calyciflorus calyciflorus, B. calyciflorus amphecerus, B. forficula, B. quadridentatus, B. urceolaris, K. cochlearis, K. tropica, K. quadrata, K. valga, N. squamula, C. gibba, C. adriatica, L. ovalis, E. dilatata, L. luna, L. bulla, L. thalera, R. neptunia, P. dolichoptera, S. oblonga, P. sulcata, T. tetractys, T. bicristata were recorded across all stations in this dynamic environment. The study showed that rotifer density varied seasonally and spatially due to changes in environmental conditions, which were considered the most significant factors affecting Rotifera density. Also, the average values of ecological indices, such as diversity, evenness, and richness, varied by season and site. 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(2025) 18 (4): 875-898. التنوع واالختالفات املكانية والزمانية للدوالبيات قي سد سامراء، العراق أسـامـة سميـر مجيـد املديرية العامة لتربية بغداد الكرخ الثالثة، وزارة التربية، بغداد، العراق 20/12/2025، النشر: 8/10/2025القبول: ،2/10/2025املراجعة: ،13/4/2025االستالم: الخالصة يعد هذا البحث األول من نوعه في هذا الخزان منذ اكثر من ثالثة عقود، ويهدف إلى تقييم تنوع في سد سامراء خالل عام املكانية والزمانية الدوالبيات واختالفاتها تم اختيار ثالث 2023ووفرة . لضمان وذلك العينات ألخذ مختلفة أسفل المحطات تقع األولى املحطة للسد. الشاملة تغطية الثالثة املحطة تقع بينما سامراء، سد من بالقرب الثانية املحطة تقع و ً مباشرة النهر مدخل من عائلة عشرة ألربع تنتمي نوعا وخمسون سبعة تشخيص تم الثرثار. ناظم من بالقرب هي ب َ ُرت ثالث الى تعود كلها Bdelloidaو Ploima ، Flosculariaceaeالدوالبيات تعود الى والتي كانت Eurotatoria.صنف وفرة األنواع Synchaeta oblonga Ehrenberg,1832،Rotariaاكثر neptunia (Ehreberg,1830) ،Euchlanis dilatate Ehrenberg, 1832 ،Polyarthra dolichoptera Idelson,1925 ، Brachionus calyciflorus Pallas, 1766 (long and short spine) ، B. urceolaris Müller, 1773 وKeratella cochlearis (Gosse, 1851). متوسط القيم كانت والتنوع والتساوي الغنى دليل من ,2.4 1.8 ,2.2 ;0.8, 1.8 ,0.8 ;6.37, 4.75 ,5.18لكل املحطات من لكل واقل 3و 2، 1بت/فرد اعلى فأن املوسمية التغايرات يخص فيما التوالي. على التوالي لكل من دليلي التساوي والتنوع سجلت في فصلي الصيف والشتاء وعلى بينما لدليل .قيم الغنى سجلت في فصلي الخريف والربيع. وبين دليل جاكرد للتشابه ان اعلى نسبة تشابه كانت بين والثالثة حيث بينما اقل نسبة كانت بين املحطة الثانية ، %68.78املحطة األولى والثالثة اذ بلغت . %7.76وصلت الى