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Valvaeodinium cookii
Valvaeodinium cookii Mantle and Riding, 2012, p.65,67, pl.8, figs.16–25.
Holotype: Mantle and Riding, 2012, pl.8, fig.25.
Age: late Bajocian–early Bathonian.
Original description (Mantle and Riding, 2012):
Valvaeodinium cookii sp. nov. (Plate VIII, 16–25)
Description: A small species of Valvaeodinium with a squat, subspherical outline and normally a flattened antapical margin. The autophragm is moderately thick (ca. 1–1.5 μm) and dark brown; the surface is scabrate to granulate with a variable density and distribution of short processes. These elements may be baculate, short capitate spines or rarely spines with blunt, bifurcate tips. The latter features are only resolvable using high power objectives. Some specimens have a relatively dense covering of these fine processes (Plate VIII, fig. 16), but they are largely confined to gonal or intergonal positions on most individuals with only a few scattered intratabular elements (Plate VIII, 17). Tabulation is indicated by the archaeopyle and low crests and ridges of variable thickness (0.5–2 μm) and distribution. These sutural features may be surmounted by short processes particularly at the gonal points and are most prominent on the hypocyst, particularly around the precingular plates. The archaeopyle is interpreted to be type AI, formed through the loss of a single apical and intercalary plate (assumed to be the 3' and 1a plates as is typical for the genus). This combination archaeopyle that leaves three apical plates in place leads to a rather pointed apex when the cyst is viewed laterally (Plate VIII, fig. 19); again, a common feature of the genus. The operculum may be free or one or both of the opercular plates may remain attached, albeit loosely. The full tabulation formula is frequently not fully resolvable, but is clearly consistent for Valvaeodinium i.e.: 4', 1a, 5'', ?6c, 5''', 1''''.
Dimensions (20 specimens measured):
Length of cyst including operculum: 28 (33) 38 μm
Equatorial width of cyst excluding spines: 29 (35) 40 μm
Length of spines: 1–3 μm
Thickness of autophragm: ca. 1–1.5 μm
Comments: Valvaeodinium cookii sp. nov. is characterized by short sutural spines, variable crests and ridges delimiting an incomplete tabulation, and a typically squat, subspherical outline. The sutural ridges vary from thin, short crests with an irregular notched to finely spinose margin (Plate VIII, 17–18), to low, thick, granular ridges (Plate VIII, 20, 23, 25). The tabulation is commonly best developed on the hypocyst where the precingular plates are typically prominent; the sutural ridges may appear as thick folds of the cyst wall.
Comparison: Valvaeodinium cookii sp. nov. is markedly less cylindrical and rather squatter and flatter-based than most other species of Valvaeodinium. The prominent tabulation is also a rare feature of the genus. Valvaeodinium euareatum Prauss 1989 is a closely comparable species from the Early to Middle Bajocian of northwest Germany. It is similarly squat with well-developed tabulation and a covering of fine, acuminate to capitate spines. However, Valvaeodinium euareatum has a much denser covering of these spines with a more even, intratabular distribution. The spines may also coalesce to form a fine reticulum; this is not a feature of V. cookii sp. nov. Furthermore, the well-defined sutural ridges of Valvaeodinium euareatum display a more complete tabulation.
Holotype and type locality: Plate VIII, fig. 25. Sunrise-2 well (2122.33 m), Bonaparte Basin, Timor Sea. Slide no. 2, EF P29/2, CPC no. 41198.
Stratigraphical distribution: Valvaeodinium cookii sp. nov. is an important marker species for the Middle Wanaea verrucosa Subzone. It first appears at the base of this subzone, together with Valvaeodinium spinosum, in both the Sunrise-2 and Sunset West- 1 wells (Fig. 4; Tables 2 and 3); it is a commoner, more consistent marker than the latter species in both wells, but its broader regional distribution is unknown. Valvaeodinium cookii sp. nov. is particularly prominent in the Sunrise-2 well, where it peaks at 3% of the total palynomorphs in sample SR10 (2117.06 m). The range top of V. cookii sp. nov. is close to the top of the Middle Wanaea verrucosa Subzone. It was not recorded in the Perseus- 3A well.
Holotype: Mantle and Riding, 2012, pl.8, fig.25.
Age: late Bajocian–early Bathonian.
Original description (Mantle and Riding, 2012):
Valvaeodinium cookii sp. nov. (Plate VIII, 16–25)
Description: A small species of Valvaeodinium with a squat, subspherical outline and normally a flattened antapical margin. The autophragm is moderately thick (ca. 1–1.5 μm) and dark brown; the surface is scabrate to granulate with a variable density and distribution of short processes. These elements may be baculate, short capitate spines or rarely spines with blunt, bifurcate tips. The latter features are only resolvable using high power objectives. Some specimens have a relatively dense covering of these fine processes (Plate VIII, fig. 16), but they are largely confined to gonal or intergonal positions on most individuals with only a few scattered intratabular elements (Plate VIII, 17). Tabulation is indicated by the archaeopyle and low crests and ridges of variable thickness (0.5–2 μm) and distribution. These sutural features may be surmounted by short processes particularly at the gonal points and are most prominent on the hypocyst, particularly around the precingular plates. The archaeopyle is interpreted to be type AI, formed through the loss of a single apical and intercalary plate (assumed to be the 3' and 1a plates as is typical for the genus). This combination archaeopyle that leaves three apical plates in place leads to a rather pointed apex when the cyst is viewed laterally (Plate VIII, fig. 19); again, a common feature of the genus. The operculum may be free or one or both of the opercular plates may remain attached, albeit loosely. The full tabulation formula is frequently not fully resolvable, but is clearly consistent for Valvaeodinium i.e.: 4', 1a, 5'', ?6c, 5''', 1''''.
Dimensions (20 specimens measured):
Length of cyst including operculum: 28 (33) 38 μm
Equatorial width of cyst excluding spines: 29 (35) 40 μm
Length of spines: 1–3 μm
Thickness of autophragm: ca. 1–1.5 μm
Comments: Valvaeodinium cookii sp. nov. is characterized by short sutural spines, variable crests and ridges delimiting an incomplete tabulation, and a typically squat, subspherical outline. The sutural ridges vary from thin, short crests with an irregular notched to finely spinose margin (Plate VIII, 17–18), to low, thick, granular ridges (Plate VIII, 20, 23, 25). The tabulation is commonly best developed on the hypocyst where the precingular plates are typically prominent; the sutural ridges may appear as thick folds of the cyst wall.
Comparison: Valvaeodinium cookii sp. nov. is markedly less cylindrical and rather squatter and flatter-based than most other species of Valvaeodinium. The prominent tabulation is also a rare feature of the genus. Valvaeodinium euareatum Prauss 1989 is a closely comparable species from the Early to Middle Bajocian of northwest Germany. It is similarly squat with well-developed tabulation and a covering of fine, acuminate to capitate spines. However, Valvaeodinium euareatum has a much denser covering of these spines with a more even, intratabular distribution. The spines may also coalesce to form a fine reticulum; this is not a feature of V. cookii sp. nov. Furthermore, the well-defined sutural ridges of Valvaeodinium euareatum display a more complete tabulation.
Holotype and type locality: Plate VIII, fig. 25. Sunrise-2 well (2122.33 m), Bonaparte Basin, Timor Sea. Slide no. 2, EF P29/2, CPC no. 41198.
Stratigraphical distribution: Valvaeodinium cookii sp. nov. is an important marker species for the Middle Wanaea verrucosa Subzone. It first appears at the base of this subzone, together with Valvaeodinium spinosum, in both the Sunrise-2 and Sunset West- 1 wells (Fig. 4; Tables 2 and 3); it is a commoner, more consistent marker than the latter species in both wells, but its broader regional distribution is unknown. Valvaeodinium cookii sp. nov. is particularly prominent in the Sunrise-2 well, where it peaks at 3% of the total palynomorphs in sample SR10 (2117.06 m). The range top of V. cookii sp. nov. is close to the top of the Middle Wanaea verrucosa Subzone. It was not recorded in the Perseus- 3A well.