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Tianjinella
From Williams et al., 2017:
[Tianjinella, He Chengquan and Sun Xuekun, 1996, p. 384–385.
Type species: Tianjinella elliptica, He Chengquan and Sun Xuekun, 1996 (pl.1, fig.1)]
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Original description: [He Chengquan and Sun Xuekun, 1996]:
Diagnosis:
Cysts proximochorate, ellipsoidal or dumbbell-shaped, rounded at both ends and without apical and antapical horns. Surface of autophragm granulate or smooth. Paracingulum expressed by equatorial constriction, parasulcus generally not indicated. Paratabulation gonyaulacacean, indicated by low, bead-shaped intratabular processes. Archeopyle apical, Type 4A or (tA).
Remarks:
Tianjinella He and Sun, gen. nov. is so peculiar that the scope for comparison with other genera is very limited. Only two genera, Dinogymniopsis Gao, He and Qiao, 1992 and Dinogymnium Evitt, Clarke and Verdier, 1967, are superficially similar to the new genus but quite different in their major characteristics. Dinogymniopsis is similar to Tianjinella He and Sun, gen. nov. in having a small, ellipsoidal or dumbbell-shaped body and an apical archeopyle but differs from the latter in lacking intratabular processes. Dinogymnium also resembles Tianjinella He and Sun, gen. nov. in basic outline, but it differs from the latter in having longitudinal folds or ribs, a very small apical archeopyle, but no indications of paratabulation such as intratabular processes.
Tianjinella has a unique morphology and can hardly be compared with other dinoflagellate cyst genera. Based on its archeopyle (apical, Type 4A or tA) and paratabulation (with 6 precingular processes and 5-6 postcingular processes, for example), we believe that this new genus is possibly related to the family Gonyaulacaceae Lindemann, 1928. However, since its parasulcus is usually not discernible and the antapical process is normally undeveloped, it is difficult to determine the exact systematic position of this genus.
Tianjinella generally occurs in large abundance and is widely distributed in the coastal region of the Bohai Sea, including the Xialiaohe area in the Liaoning Province, the Dagang area in southern Tianjin and the Dongying area in the Shandong Province, but stratigraphically it is restricted to the upper part of Member 3 of the Shahejie Formation (Eocene). This indicates that Tianjinella could be a potentially useful biostratigraphic marker for the Eocene strata in this region.
In the studied material Tianjinella was found in association with cysts of other dinoflagellate genera such as Oligosphaeridium Davey and Williams, 1966, Hystrichosphaeridium Deflandre, 1937, Songiella Sun, 1994, Bohaidina Jiabo, 1978 and Parabohaidina Jiabo, 1978, etc., but neither typical freshwater fossils (e.g. Pediastrum Meyen, 1829) nor typical marine forms (e.g. calcareous nannofossils or foraminifera) were found in this material. In addition, the dinoflagellate assemblage containing Tianjinella has a high abundance and a low diversity, with less than 10 genera being encountered. These results indicate that Tianjinella is probably associated with a brackish-water environment.
[Tianjinella, He Chengquan and Sun Xuekun, 1996, p. 384–385.
Type species: Tianjinella elliptica, He Chengquan and Sun Xuekun, 1996 (pl.1, fig.1)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [He Chengquan and Sun Xuekun, 1996]:
Diagnosis:
Cysts proximochorate, ellipsoidal or dumbbell-shaped, rounded at both ends and without apical and antapical horns. Surface of autophragm granulate or smooth. Paracingulum expressed by equatorial constriction, parasulcus generally not indicated. Paratabulation gonyaulacacean, indicated by low, bead-shaped intratabular processes. Archeopyle apical, Type 4A or (tA).
Remarks:
Tianjinella He and Sun, gen. nov. is so peculiar that the scope for comparison with other genera is very limited. Only two genera, Dinogymniopsis Gao, He and Qiao, 1992 and Dinogymnium Evitt, Clarke and Verdier, 1967, are superficially similar to the new genus but quite different in their major characteristics. Dinogymniopsis is similar to Tianjinella He and Sun, gen. nov. in having a small, ellipsoidal or dumbbell-shaped body and an apical archeopyle but differs from the latter in lacking intratabular processes. Dinogymnium also resembles Tianjinella He and Sun, gen. nov. in basic outline, but it differs from the latter in having longitudinal folds or ribs, a very small apical archeopyle, but no indications of paratabulation such as intratabular processes.
Tianjinella has a unique morphology and can hardly be compared with other dinoflagellate cyst genera. Based on its archeopyle (apical, Type 4A or tA) and paratabulation (with 6 precingular processes and 5-6 postcingular processes, for example), we believe that this new genus is possibly related to the family Gonyaulacaceae Lindemann, 1928. However, since its parasulcus is usually not discernible and the antapical process is normally undeveloped, it is difficult to determine the exact systematic position of this genus.
Tianjinella generally occurs in large abundance and is widely distributed in the coastal region of the Bohai Sea, including the Xialiaohe area in the Liaoning Province, the Dagang area in southern Tianjin and the Dongying area in the Shandong Province, but stratigraphically it is restricted to the upper part of Member 3 of the Shahejie Formation (Eocene). This indicates that Tianjinella could be a potentially useful biostratigraphic marker for the Eocene strata in this region.
In the studied material Tianjinella was found in association with cysts of other dinoflagellate genera such as Oligosphaeridium Davey and Williams, 1966, Hystrichosphaeridium Deflandre, 1937, Songiella Sun, 1994, Bohaidina Jiabo, 1978 and Parabohaidina Jiabo, 1978, etc., but neither typical freshwater fossils (e.g. Pediastrum Meyen, 1829) nor typical marine forms (e.g. calcareous nannofossils or foraminifera) were found in this material. In addition, the dinoflagellate assemblage containing Tianjinella has a high abundance and a low diversity, with less than 10 genera being encountered. These results indicate that Tianjinella is probably associated with a brackish-water environment.