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Dapcodinium brenneri
Dapcodinium brenneri sp. nov., Mantle et al. 2020, p. 36
Holotype: Mantle et al. 2020, Plate IX, 10
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (late Carnian to Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate to weakly cavate, ovoidal to subrhomboidal dinoflagellate cysts with a constricted apex and a comprehensively folded periphragm.
Wall: endophragm and periphragm are typically closely appressed although minor wall separation of 1–3 μm is occasionally evident antapically, or around the margins of the archaeopyle. The periphragm is smooth to scabrate with abundant, irregular, fine folds. Both wall layers commonly thin towards the apex. The pervasive folds mask any indications of tabulation other than the low sutural ridges bordering the broad cingulum. The cingulum profile varies from concave to straight-sided to rarely convex. The full tabulation formula is unknown.
Archaeopyle: nature not known, but it is formed through the loss of both apical and anterior intercalary plates. A dark brown accumulation body is commonly present close to the cingulum.
Dimensions:
Overall length 28 μm (34 μm) 42 μm; maximum width 25 μm (29 μm) 37 μm
16 measured specimens
Remarks:
Dapcodinium brenneri sp. nov. was previously questionably attributed to Noricysta by Brenner (1992) and Backhouse and Balme (2002) due to its partially cavate cyst organisation. However, this form exhibits several features typical of Dapcodinium. These include a combination archaeopyle involving the loss of both apical and anterior intercalary plates and a broad, albeit poorly defined, cingulum. The extensive folding or wrinkled appearance of the periphragm, together with both wall layers commonly thinning apically, are also common features of Dapcodinium.
Affinities/Comparisons:
Dapcodinium brenneri sp. nov. is most similar to Dapcodinium tabulodiniopsis sp. nov. Both species are broadly similar in size and shape, and may develop minor cavation. However, Dapcodinium brenneri sp. nov. is readily differentiated by the dense, thin, irregular folds on the periphragm, the lack of well-defined tabulation and the narrower apical region. Most other species of Dapcodinium have a much more well-defined ambitus, as opposed to the somewhat irregular and “shrivelled” margin of Dapcodinium brenneri sp. nov., and they also lack pervasive periphragmal folds and a substantially constricted apex.
Holotype: Mantle et al. 2020, Plate IX, 10
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (late Carnian to Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate to weakly cavate, ovoidal to subrhomboidal dinoflagellate cysts with a constricted apex and a comprehensively folded periphragm.
Wall: endophragm and periphragm are typically closely appressed although minor wall separation of 1–3 μm is occasionally evident antapically, or around the margins of the archaeopyle. The periphragm is smooth to scabrate with abundant, irregular, fine folds. Both wall layers commonly thin towards the apex. The pervasive folds mask any indications of tabulation other than the low sutural ridges bordering the broad cingulum. The cingulum profile varies from concave to straight-sided to rarely convex. The full tabulation formula is unknown.
Archaeopyle: nature not known, but it is formed through the loss of both apical and anterior intercalary plates. A dark brown accumulation body is commonly present close to the cingulum.
Dimensions:
Overall length 28 μm (34 μm) 42 μm; maximum width 25 μm (29 μm) 37 μm
16 measured specimens
Remarks:
Dapcodinium brenneri sp. nov. was previously questionably attributed to Noricysta by Brenner (1992) and Backhouse and Balme (2002) due to its partially cavate cyst organisation. However, this form exhibits several features typical of Dapcodinium. These include a combination archaeopyle involving the loss of both apical and anterior intercalary plates and a broad, albeit poorly defined, cingulum. The extensive folding or wrinkled appearance of the periphragm, together with both wall layers commonly thinning apically, are also common features of Dapcodinium.
Affinities/Comparisons:
Dapcodinium brenneri sp. nov. is most similar to Dapcodinium tabulodiniopsis sp. nov. Both species are broadly similar in size and shape, and may develop minor cavation. However, Dapcodinium brenneri sp. nov. is readily differentiated by the dense, thin, irregular folds on the periphragm, the lack of well-defined tabulation and the narrower apical region. Most other species of Dapcodinium have a much more well-defined ambitus, as opposed to the somewhat irregular and “shrivelled” margin of Dapcodinium brenneri sp. nov., and they also lack pervasive periphragmal folds and a substantially constricted apex.