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Dapcodinium prolongatum
Dapcodinium prolongatum sp. nov., Mantle et al. 2020, p. 38
Holotype: Mantle et al. 2020, Plate VIII, 2
Type locality: Browse Basin, Western Australia
Local stratigraphical range: Late Triassic (Norian–Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate or cavate, pyriform to ovoidal dinoflagellate cysts with a subrounded, lobate or flat-based hemispherical hypocyst and a variably tapered conate epicyst.
Wall: epicyst is much thinner walled, particularly the climactal plates, and thus superficially appears to be epicavate (there is no evidence of epicavation). Conversely, the endophragm and periphragm are frequently separated by 1–3 μm antapically (Plate VIII, 24, 25). The surface ornament is typically scabrate to granulate or occasionally microreticulate or microrugulate. Low sutural ridges define an incomplete tabulation.
Tabulation: n′, 4+a, 7′′, nc, 6/7′′′, n′′′′, ns.
The relatively broad (3–5 μm) cingulum is largely undivided, with only rare hints of internal tabulation and typically is not indented.
Archaeopyle: compound combination, involves the loss of the mediodorsal apical and anterior intercalary plates, most likely 3′, 4′, 2a, and 3a (see Fig. 5b). However, because the complete epicystal
tabulation is not known, the exact plate equivalence of the operculum is unconfirmed.
Dimensions:
Overall length (excluding the apical plates) 26 μm (32 μm) 43 μm; maximum width 21 μm (28 μm) 34 μm
20 measured specimens
Remarks:
The pear-shaped or tear-drop ambitus is the most diagnostic feature of Dapcodinium prolongatum sp. nov., and this trait is further emphasised by the substantially thinner walled climactal plates. The tabulation formula of n′, 4+a, 7′′, nc, 6/7′′′, n′′′′, ns for Dapcodinium prolongatum sp. nov. is apparently largely consistent with the tabulation of Dapcodinium as documented by Below (1987), i.e. PR, 5′, 4–6a, 7′′, 8c, 6–8′′′, 3′′′′, ns.
Affinities/Comparisons:
Dapcodinium morganii sp. nov., Dapcodinium ovale, and Dapcodinium priscum all lack the diagnostic thin-walled apical horn and conate epicyst of Dapcodinium prolongatum sp. nov. Furthermore, Dapcodinium morganii sp. nov and Dapcodinium ovale are both typically ovoidal, and may be more densely microrugulate or finely wrinkled than Dapcodinium prolongatum sp. nov. Dapcodinium priscum is generally much more strongly tabulate than Dapcodinium prolongatum sp. nov., and typically has a broader cingulum that may also be strongly indented.
Holotype: Mantle et al. 2020, Plate VIII, 2
Type locality: Browse Basin, Western Australia
Local stratigraphical range: Late Triassic (Norian–Rhaetian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate or cavate, pyriform to ovoidal dinoflagellate cysts with a subrounded, lobate or flat-based hemispherical hypocyst and a variably tapered conate epicyst.
Wall: epicyst is much thinner walled, particularly the climactal plates, and thus superficially appears to be epicavate (there is no evidence of epicavation). Conversely, the endophragm and periphragm are frequently separated by 1–3 μm antapically (Plate VIII, 24, 25). The surface ornament is typically scabrate to granulate or occasionally microreticulate or microrugulate. Low sutural ridges define an incomplete tabulation.
Tabulation: n′, 4+a, 7′′, nc, 6/7′′′, n′′′′, ns.
The relatively broad (3–5 μm) cingulum is largely undivided, with only rare hints of internal tabulation and typically is not indented.
Archaeopyle: compound combination, involves the loss of the mediodorsal apical and anterior intercalary plates, most likely 3′, 4′, 2a, and 3a (see Fig. 5b). However, because the complete epicystal
tabulation is not known, the exact plate equivalence of the operculum is unconfirmed.
Dimensions:
Overall length (excluding the apical plates) 26 μm (32 μm) 43 μm; maximum width 21 μm (28 μm) 34 μm
20 measured specimens
Remarks:
The pear-shaped or tear-drop ambitus is the most diagnostic feature of Dapcodinium prolongatum sp. nov., and this trait is further emphasised by the substantially thinner walled climactal plates. The tabulation formula of n′, 4+a, 7′′, nc, 6/7′′′, n′′′′, ns for Dapcodinium prolongatum sp. nov. is apparently largely consistent with the tabulation of Dapcodinium as documented by Below (1987), i.e. PR, 5′, 4–6a, 7′′, 8c, 6–8′′′, 3′′′′, ns.
Affinities/Comparisons:
Dapcodinium morganii sp. nov., Dapcodinium ovale, and Dapcodinium priscum all lack the diagnostic thin-walled apical horn and conate epicyst of Dapcodinium prolongatum sp. nov. Furthermore, Dapcodinium morganii sp. nov and Dapcodinium ovale are both typically ovoidal, and may be more densely microrugulate or finely wrinkled than Dapcodinium prolongatum sp. nov. Dapcodinium priscum is generally much more strongly tabulate than Dapcodinium prolongatum sp. nov., and typically has a broader cingulum that may also be strongly indented.