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Hystrichostrogylon crassitunicatum
Original description: [Vasilyeva, 2024, p. 7]:
Hystrichostrogylon crassitunicatum sp. nov.
Plate 2, figures 13–24; Figure 5
Derivation of name. After the Latin crassitunicatus – thickwalled – referring to the morphology of the cysts which possess a dense, thick cell membrane.
Holotype. Plate 2, figure 13. Slide R43/46-B, coordinates 102 x 13, lateral view. Ravninnaya R43 borehole, sample 46, the Keresta Formation, collection number IGG-2/23-04. Specimen dimensions: pericyst length 54 mm, pericyst width 58 mm, endocyst diameter 36–39 mm, length of processes 10–11 mm, wall thickness 10 mm, cingulum width 14 mm, pericoel height 7–8 mm.
Paratype. Plate 2, figures 17, 18. Slide R43/47A, coordinates 109 x 20, dorsal view, figure 17 – high focus, figure 18 – middle focus. Ravninnaya R43 borehole, sample 47, Keresta Formation, collection number IGG-2/23-05. Specimen dimensions: pericyst length 54 mm, pericyst width 50 mm, endocyst diameter 40–36 mm, length of processes 7–8 mm, wall thickness 7–8 mm, cingulum width 14 mm, pericoel height 7 mm.
Type locality. The village of Ravninny in the vicinity of Volgograd, Volgograd region, Russia.
Type stratum. The Keresta Formation, the Volga–Caspian subregion.
Diagnosis. Gonyaulacoid proximate/proximochorate camocavate cysts of subspherical shape and small size. The cyst has a thick two-layered granulated wall, with its division making a narrow pericoel on the ventral surface.
Description. The wall is formed by periphragm and endophragm; both are dense, thick-walled, acinose, granular (Plate 2, figures 15, 19, 24). Periphragm and endophragm are tightly pressed all over the surface, except for the ventral side; they separate there to make a low-volume domeshaped pericoel (Plate 2, figures 13–15). Processes are gonal and sutural, comparatively short, trifurcate and bifurcate, hollow, closed, proximally dilated. Shorter processes occur onthe pericoel. Thin sutural ribs/seams are formed between the processes (Plate 2, figures 16, 19, 20). Archaeopyle is large, pentagonal, distinct, precingular in location; type P (3ʺ). Operculum is free. Tabulation is marked by archaeopyle, cingulum, processes and sutures; not pronounced in full (Figure 5). Sulcus is not distinguishable.
Dimensions. Pericyst length 43 (48) 56 mm, pericyst width 41 (49) 58 mm, endocyst diameter 29 (33) 40 mm, process length 4–11 mm, wall thickness 4–7 mm, cingulum width 7–14 mm, pericoel height 7–8 mm. Number of specimens measured: 10.
Comparison. Hystrichostrogylon crassitunicatum sp. nov. differs from other species of Hystrichostrogylon in comparatively small size, thick granular wall and relatively narrow pericoel (Figure 5). Hystrichostrogylon membraniphorum subsp. granulatum has a granular endophragm, but unlike Hystrichostrogylon crassitunicatum sp. nov., it has a wide pericoel and long processes (Heilmann-Clausen and Costa 1989). Unlike the new form, Hystrichostrogylon clausenii cysts are much larger and have a strongly expanded pericoel, and thin and smooth walls. The species Hystrichostrogylon crassitunicatum sp. nov. is comparable with Hystrichostrogylon sulcatum in terms of medium size, narrow pericoel, and relatively short processes. However, the latter species differs in the structure of the pericoel, limited by the sulcal zone, the subconical shape of the processes, the morphology of the antapical processes (proximally connected by a wide membrane), and the presence of a thin apical process (Guerstein et al. 2004).
Occurrence. The south of the Russian Platform, Keresta Formation, in the Ravninnaya R43 borehole, Volgograd Volga region. Middle Eocene, Lutetian stage.
Hystrichostrogylon crassitunicatum sp. nov.
Plate 2, figures 13–24; Figure 5
Derivation of name. After the Latin crassitunicatus – thickwalled – referring to the morphology of the cysts which possess a dense, thick cell membrane.
Holotype. Plate 2, figure 13. Slide R43/46-B, coordinates 102 x 13, lateral view. Ravninnaya R43 borehole, sample 46, the Keresta Formation, collection number IGG-2/23-04. Specimen dimensions: pericyst length 54 mm, pericyst width 58 mm, endocyst diameter 36–39 mm, length of processes 10–11 mm, wall thickness 10 mm, cingulum width 14 mm, pericoel height 7–8 mm.
Paratype. Plate 2, figures 17, 18. Slide R43/47A, coordinates 109 x 20, dorsal view, figure 17 – high focus, figure 18 – middle focus. Ravninnaya R43 borehole, sample 47, Keresta Formation, collection number IGG-2/23-05. Specimen dimensions: pericyst length 54 mm, pericyst width 50 mm, endocyst diameter 40–36 mm, length of processes 7–8 mm, wall thickness 7–8 mm, cingulum width 14 mm, pericoel height 7 mm.
Type locality. The village of Ravninny in the vicinity of Volgograd, Volgograd region, Russia.
Type stratum. The Keresta Formation, the Volga–Caspian subregion.
Diagnosis. Gonyaulacoid proximate/proximochorate camocavate cysts of subspherical shape and small size. The cyst has a thick two-layered granulated wall, with its division making a narrow pericoel on the ventral surface.
Description. The wall is formed by periphragm and endophragm; both are dense, thick-walled, acinose, granular (Plate 2, figures 15, 19, 24). Periphragm and endophragm are tightly pressed all over the surface, except for the ventral side; they separate there to make a low-volume domeshaped pericoel (Plate 2, figures 13–15). Processes are gonal and sutural, comparatively short, trifurcate and bifurcate, hollow, closed, proximally dilated. Shorter processes occur onthe pericoel. Thin sutural ribs/seams are formed between the processes (Plate 2, figures 16, 19, 20). Archaeopyle is large, pentagonal, distinct, precingular in location; type P (3ʺ). Operculum is free. Tabulation is marked by archaeopyle, cingulum, processes and sutures; not pronounced in full (Figure 5). Sulcus is not distinguishable.
Dimensions. Pericyst length 43 (48) 56 mm, pericyst width 41 (49) 58 mm, endocyst diameter 29 (33) 40 mm, process length 4–11 mm, wall thickness 4–7 mm, cingulum width 7–14 mm, pericoel height 7–8 mm. Number of specimens measured: 10.
Comparison. Hystrichostrogylon crassitunicatum sp. nov. differs from other species of Hystrichostrogylon in comparatively small size, thick granular wall and relatively narrow pericoel (Figure 5). Hystrichostrogylon membraniphorum subsp. granulatum has a granular endophragm, but unlike Hystrichostrogylon crassitunicatum sp. nov., it has a wide pericoel and long processes (Heilmann-Clausen and Costa 1989). Unlike the new form, Hystrichostrogylon clausenii cysts are much larger and have a strongly expanded pericoel, and thin and smooth walls. The species Hystrichostrogylon crassitunicatum sp. nov. is comparable with Hystrichostrogylon sulcatum in terms of medium size, narrow pericoel, and relatively short processes. However, the latter species differs in the structure of the pericoel, limited by the sulcal zone, the subconical shape of the processes, the morphology of the antapical processes (proximally connected by a wide membrane), and the presence of a thin apical process (Guerstein et al. 2004).
Occurrence. The south of the Russian Platform, Keresta Formation, in the Ravninnaya R43 borehole, Volgograd Volga region. Middle Eocene, Lutetian stage.