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Sverdrupiella rhaetica
Sverdrupiella rhaetica sp. nov., Mantle et al. 2020, p. 46
Holotype: Mantle et al. 2020, Plate XVII, 12
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, cavate to bicavate dinoflagellate cysts with a relatively dark, ovoidal endocyst and a thin-walled periphragm that forms a short, conate apical horn (2–10 μm long) and encloses an irregular antapical pericoel (3–11 μm in diameter).
Wall: antapical periphragm may form a rounded protuberance, or a larger angular pericoel, often with a broadly serrated or pyramidal posterior margin, that is commonly asymmetrically offset from the midline. The endophragm is smooth to scabrate, with many broad folds and a conspicuous dark accumulation body close to the cingulum. The periphragm is scabrate, finely granulate or irregularly microreticulate with numerous finer folds and rugulae. The extensive folds in the periphragm largely obscure the very sparse low sutural ridges (where present); only the cingulum is commonly identifiable
Tabulation formula: undetermined
Archaeopyle: typically not clear, but very rare specimens exhibit mid-dorsal intercalary or postapical plates with angular anterior margins that likely represent opercular plates.
Dimensions:
Overall length of the pericyst 37 μm (41 μm) 60 μm; maximum width 23 μm (28 μm) 44 μm
20 measured specimens
Remarks:
This species is attributed to Sverdrupiella because it is distinctively cavate to bicavate with a weakly expressed tabulation and a probable anterior intercalary archaeopyle. Although Hebecysta also displays some separation of the periphragm and endophragm, the cavation is not as well-developed as in Sverdrupiella.
Affinities/Comparisons:
Sverdrupiella rhaetica sp. nov. is significantly smaller than all other species of the genus. It is also present in the Rhaetian, as opposed to the predominantly Norian age of most other species of Sverdrupiella. Furthermore, Sverdrupiella rhaetica sp. nov. lacks the prominent spines and verrucae of many of the Norian species. It is most similar to the smooth, less elongate forms of Sverdrupiella mutabilis Bujak and Fisher, 1976, but is still notably shorter, less biconical and with substantially smaller cavation and horn development.
Holotype: Mantle et al. 2020, Plate XVII, 12
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, cavate to bicavate dinoflagellate cysts with a relatively dark, ovoidal endocyst and a thin-walled periphragm that forms a short, conate apical horn (2–10 μm long) and encloses an irregular antapical pericoel (3–11 μm in diameter).
Wall: antapical periphragm may form a rounded protuberance, or a larger angular pericoel, often with a broadly serrated or pyramidal posterior margin, that is commonly asymmetrically offset from the midline. The endophragm is smooth to scabrate, with many broad folds and a conspicuous dark accumulation body close to the cingulum. The periphragm is scabrate, finely granulate or irregularly microreticulate with numerous finer folds and rugulae. The extensive folds in the periphragm largely obscure the very sparse low sutural ridges (where present); only the cingulum is commonly identifiable
Tabulation formula: undetermined
Archaeopyle: typically not clear, but very rare specimens exhibit mid-dorsal intercalary or postapical plates with angular anterior margins that likely represent opercular plates.
Dimensions:
Overall length of the pericyst 37 μm (41 μm) 60 μm; maximum width 23 μm (28 μm) 44 μm
20 measured specimens
Remarks:
This species is attributed to Sverdrupiella because it is distinctively cavate to bicavate with a weakly expressed tabulation and a probable anterior intercalary archaeopyle. Although Hebecysta also displays some separation of the periphragm and endophragm, the cavation is not as well-developed as in Sverdrupiella.
Affinities/Comparisons:
Sverdrupiella rhaetica sp. nov. is significantly smaller than all other species of the genus. It is also present in the Rhaetian, as opposed to the predominantly Norian age of most other species of Sverdrupiella. Furthermore, Sverdrupiella rhaetica sp. nov. lacks the prominent spines and verrucae of many of the Norian species. It is most similar to the smooth, less elongate forms of Sverdrupiella mutabilis Bujak and Fisher, 1976, but is still notably shorter, less biconical and with substantially smaller cavation and horn development.