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Recent Ostracoda from the Northeastern part of Osaka Bay, Southwestern Japan

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Ostracodes from Osaka Bay, southwestern Japan, were quantitatively studied in order to examine the relationships between environmental factors and species distribution. At least 109 species belonging to 43 genera were identified from 31 surface sediment samples. On the basis of Q-mode cluster analysis, four biotopes (A, B, C and D) are recognized. Characteristic species of each biotope are as follows: A (central bay at 17.2-37.2 m water depth), Trachyleberis scabrocuneata, Cytheropteron miurense, Kobayashiina donghaiensis, Schizocythere kishinouyei and Krithe japonica; B (inner part of the bay at 16.3-21. 1 m water depth), Bicornucythere bisanensis (form A), Bicornucythere bisanensis (form M), Cytheromorpha acupunctata, Loxoconcha viva and Nipponocythere bicarinata; C (innermost part of the bay at 9.2-15.9 m water depth), B. bisanensis (form A), Loxoconcha tosaensis and Spinileberis quadriaculeata; D (inner part of the bay at 12.6 m water depth), C. acupunctata. These results suggest that species distribution is controlled by bathymetry. High abundance and high species diversities are found in the westernmost area. In contrast, low abundance and low species diversities are observed in the eastern area, where water masses with low dissolved oxygen content spread, especially in the summer. It is shown that the tidal current and the dissolved oxygen contents strongly influence abundance and species diversity of ostracodes in Osaka Bay.
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... 1-5 sensu Irizuki (1994); Semicytherura sp. sensu Irizuki et al. (2005); Semicytherura sp. 1 sensu Yasuhara and Irizuki (2001); Semicytherura sp. 2 sensu Yamada et al. (2002); Semicytherura sp. 1-2 sensu ; Semicytherura sp. ...
... 11, fig. 8 in Yasuhara and Irizuki 2001). This variation in number of anteroventral denticles indicates that the specimens of Yasuhara and Irizuki (2001) belong to S. kazahana (Fig. 4H), unless they present juvenile and adult of separate species. ...
... 8 in Yasuhara and Irizuki 2001). This variation in number of anteroventral denticles indicates that the specimens of Yasuhara and Irizuki (2001) belong to S. kazahana (Fig. 4H), unless they present juvenile and adult of separate species. However, although the geographical distribution of S. kazahana and S. sasameyuki overlaps, their microhabitats differ with the former being a phytal species typical of rocky shore environments, and the latter living on the silty sands of inner bays (Yamada et al. 2005). ...
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... 22 in Fig. 1) (Abe 1988) and Osaka Bay (Loc. 10 in Fig. 1) (Yasuhara & Irizuki 2001). In the present study, we compared the morphology of the male copulatory organs of various specimens of the genus Bicornucythere, which is widely distributed across the inner bays of Japan, to identify a new species and report patterns of morphological variation. ...
Article
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... Ostracoda distribution depends on environmental factors such as substrates, water temperature, water depth, salinity, and hydrochemical gradients (Smith, 1993;Yasuhara and Irizuki, 2001;Rumes et al., 2016). Ecologically, silty sand and sand are the most favorable substrates for Ostracod growth (Sridhar et al., 2002). ...
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... For abundant species (i.e., Horn), we observed a distinct "Victoria Harbour + Eastern Buffer" biofacies (Figs. 6 and 7). These Victoria Harbour and "Victoria Harbour + Eastern Buffer" biofacies are characterized by sand dwellers (Cytheropteron miurense, Pistocythereis bradyformis, Loxoconcha epeterseni) and phytal taxa (Aurila, Neonesidea, Xestoleberis) ( Fig. 9; Table 2) (Yasuhara and Irizuki, 2001;Yasuhara et al., 2002). So, Mud or intermediate-level productivity may play a role not only in diversity as discussed above but also in faunal composition. ...
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... Ostracods were picked from the coarse fraction. We identified ostracod taxa by referring to Ishizaki (1968), Yasuhara and Irizuki (2001), and Irizuki et al. (2008). We counted the number of valves and valve fragments of each taxon. ...
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