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Egmontodinium twiggii
Synonymy: Egmontodinium sp. A (Mantle, 2009a, p. 99, pl. 13, 5ab) Previous Australian usage: Egmontodinium sp. A (Sinclair, 2012), Egmontodinium cf. toryna, Egmontodinium ‘twiggy’ (unpublished well reports)
Holotype: Plate III, 1–3
Diagnosis: A species of Egmontodinium with a smooth to granulate autophragm adorned with numerous short, bifurcate or capitate, sutural and intratabular processes sometimes forming discontinuous septa. Tabulation gonyaulacacean, cingulum well-defined by the absence of intratabular processes. Archeopyle apical, Type (tA), operculum free.
Etymology: ‘twiggii’ in reference to the twig-like appearance of the processes, as first used in Marshall (1996).
Material: Palynological strew samples; 2811 m, Jansz-1; 2903 m, Jansz-2; 3820 m, Jansz-3, 3215.62 m, Laminaria-2; 3066.94 m, 3074.9 m 3076.9 m, Pyxis-1.
Age: Bathonian–Kimmeridgian (T. balmei–D. swanense zones; Fig. 5), more abundant in the late Oxfordian–Kimmeridgian. the Bonaparte Basin. The Legendre Fm–Dingo Claystone of the Northern Carnarvon Basin.
Description: An intermediate, elongate ellipsoidal, acavate dinoflagellate cyst. Autophragm smooth to granulate, covered in numerous small, sutural and intratabular processes that are subcircular to flattened in cross-section, and may be flared both proximally and distally. Processes are capitate, weakly bifurcate, or rarely trifurcate. Adjacent processes are frequently connected by low proximal crests, or coalesce to form discontinuous stauromate septa, most commonly along sutural margins. Very rarely, processes may be distally linked by short trabeculae. Processes adjoining the cingular margin are usually more prominent. Standard gonyaulacacean tabulation indicated by the alignment of sutural elements, formula:?pr, 4′, 6″,?6c, 6″’, 1p1″”,?s (Fig. 7). Cingulum always well-defined by the absence of intratabular processes, and typically lacks internal subdivision; sulcal plates rarely defined. Archeopyle apical, Type (tA),with aweakly indented sulcal notch; operculum free.
Dimensions: (30 specimens measured)
Length (including operculum): 59 (62) 73
Length (excluding operculum): 55 (65) 74
Maximum width: 24 (31) 42
Maximum process length: 2 (5) 7
Comparison and remarks: Egmontodinium twiggii is similar to E. toryna in presenting sutural and intratabular processes and differs from it by having shorter, thinner and more numerous processes, in particular a greater number of intratabular processes. Egmontodinium twiggii is superficially similar to Productodinium chenii Davey, 1988 but differs in having a well-defined cingulum and partial/complete tabulation indicated by sutural processes (3–7 μm) that vary between distally flared, capitate and furcate forms.
Intratabular process density is greater in stratigraphically older specimens and typically ranges between 0 and 15/plate, depending on the size and position of the plate. Typically, pre- and postcingular plates, exhibit a greater number of intratabular processes. Cysts are usually ellipsoidal but may be dorsoventrally flattened.
Holotype: Plate III, 1–3
Diagnosis: A species of Egmontodinium with a smooth to granulate autophragm adorned with numerous short, bifurcate or capitate, sutural and intratabular processes sometimes forming discontinuous septa. Tabulation gonyaulacacean, cingulum well-defined by the absence of intratabular processes. Archeopyle apical, Type (tA), operculum free.
Etymology: ‘twiggii’ in reference to the twig-like appearance of the processes, as first used in Marshall (1996).
Material: Palynological strew samples; 2811 m, Jansz-1; 2903 m, Jansz-2; 3820 m, Jansz-3, 3215.62 m, Laminaria-2; 3066.94 m, 3074.9 m 3076.9 m, Pyxis-1.
Age: Bathonian–Kimmeridgian (T. balmei–D. swanense zones; Fig. 5), more abundant in the late Oxfordian–Kimmeridgian. the Bonaparte Basin. The Legendre Fm–Dingo Claystone of the Northern Carnarvon Basin.
Description: An intermediate, elongate ellipsoidal, acavate dinoflagellate cyst. Autophragm smooth to granulate, covered in numerous small, sutural and intratabular processes that are subcircular to flattened in cross-section, and may be flared both proximally and distally. Processes are capitate, weakly bifurcate, or rarely trifurcate. Adjacent processes are frequently connected by low proximal crests, or coalesce to form discontinuous stauromate septa, most commonly along sutural margins. Very rarely, processes may be distally linked by short trabeculae. Processes adjoining the cingular margin are usually more prominent. Standard gonyaulacacean tabulation indicated by the alignment of sutural elements, formula:?pr, 4′, 6″,?6c, 6″’, 1p1″”,?s (Fig. 7). Cingulum always well-defined by the absence of intratabular processes, and typically lacks internal subdivision; sulcal plates rarely defined. Archeopyle apical, Type (tA),with aweakly indented sulcal notch; operculum free.
Dimensions: (30 specimens measured)
Length (including operculum): 59 (62) 73
Length (excluding operculum): 55 (65) 74
Maximum width: 24 (31) 42
Maximum process length: 2 (5) 7
Comparison and remarks: Egmontodinium twiggii is similar to E. toryna in presenting sutural and intratabular processes and differs from it by having shorter, thinner and more numerous processes, in particular a greater number of intratabular processes. Egmontodinium twiggii is superficially similar to Productodinium chenii Davey, 1988 but differs in having a well-defined cingulum and partial/complete tabulation indicated by sutural processes (3–7 μm) that vary between distally flared, capitate and furcate forms.
Intratabular process density is greater in stratigraphically older specimens and typically ranges between 0 and 15/plate, depending on the size and position of the plate. Typically, pre- and postcingular plates, exhibit a greater number of intratabular processes. Cysts are usually ellipsoidal but may be dorsoventrally flattened.