Back
Heibergella obelixii
Heibergella? obelixii sp. nov., Mantle et al. 2020, p. 44 - 45
Holotype: Mantle et al. 2020, Plate XV, 6a, b
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (upper Carnian and lowermost Norian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate, ovoidal to biconical dinoflagellate cysts with a very short conate apical horn or bluntly rounded apex and a broadly hemispherical hypocyst.
Wall: autophragm is scabrate to coarsely granulate and some areas of denser ornamentation may appear spongy. The very broad cingulum (8–12 μm) and posterior sulcal margin are highlighted by the alignment of coarser grana, frequently conferring a weakly serrated edge to these sutures. The cingular margins may also be marked by low folds or ridges.
Tabulation: typically only indicated by these cingular and sulcal boundaries, or by the archaeopyle margin and accessory archaeopyle sutures. However, rare clusters of coarser, intratabular grana may also denote some of the precingular and intercalary plates, along with the rare alignment of sutural grana distal to the cingulum and sulcus. The cingulum is moderately laevorotary and is undivided.
Full tabulation formula: undetermined (?PR, n′, 4–5a, 6+′′, nc, n′′′, n′′′′, ns)
Archaeopyle: formed through the compound loss of one to three anterior intercalary plates.
Dimensions:
Overall length 37 μm (43 μm) 49 μm; maximum width 30 μm (38 μm) 43 μm
20 measured specimens
Remarks:
The ovoidal to biconical shape, very broad cingulum with aligned coarser grana, well-defined posterior sulcal margin and the loss of up to three anterior intercalary plates in Heibergella? obelixii sp. nov. invites comparison to Rhaetogonyaulax nagelii sp. nov. And Rhaetogonyaulax wigginsii. However, as there is no suggestion of further plate loss in archaeopyle formation, and the epicyst is conate rather than forming a true apical horn, this new species is questionably placed in Heibergella herein.
Affinities/Comparison:
Heibergella? obelixii sp. nov. is smaller than all previously published species of this genus, and it has a notably broader cingulum which is reminiscent of Rhaetogonyaulax. It differs further from the type species, Heibergella asymmetrica Bujak and Fisher, 1976, in possessing a coarsely granulate autophragm and lacking a pronounced apical horn. The other species of Heibergella described by Bujak and Fisher (1976) from the Canadian Arctic, i.e., Heibergella aculeata and Heibergella salebrosacea, are strongly biconical with longer apical horns and have short, acuminate antapical horns. Thus, these differ substantially from the hemispherical to flat-based antapex of Heibergella? obelixii sp. nov. The dense covering of spines and the frequent second antapical horn further distinguish Heibergella aculeata. Although Morbey (1975, pl. 14, fig. 2) considered Rhombodella kendelbachia to have an apical archaeopyle, the author appears to have illustrated a specimen with mechanical damage around the apex. Thus, this taxon was transferred to Heibergella by Lentin and Williams (1981). Heibergella kendelbachia is distinguished from Heibergella? obelixii sp. nov., by its more strongly rhomboidal outline, with a far less pronounced cingulum or sulcus. It differs further in occasionally possessing short (up to 2 μm) processes that are “tapered, cylindrical” and with “slender hair-like stems and simple or bifurcate terminations.” However, these processes are also not readily discernable in the type material (Morbey, 1975, pl. 14, figs. 1–4, pl. 17, figs. 1–3).
Holotype: Mantle et al. 2020, Plate XV, 6a, b
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (upper Carnian and lowermost Norian)
Original description: Mantle et al. 2020:
Description:
Small, proximate, acavate, ovoidal to biconical dinoflagellate cysts with a very short conate apical horn or bluntly rounded apex and a broadly hemispherical hypocyst.
Wall: autophragm is scabrate to coarsely granulate and some areas of denser ornamentation may appear spongy. The very broad cingulum (8–12 μm) and posterior sulcal margin are highlighted by the alignment of coarser grana, frequently conferring a weakly serrated edge to these sutures. The cingular margins may also be marked by low folds or ridges.
Tabulation: typically only indicated by these cingular and sulcal boundaries, or by the archaeopyle margin and accessory archaeopyle sutures. However, rare clusters of coarser, intratabular grana may also denote some of the precingular and intercalary plates, along with the rare alignment of sutural grana distal to the cingulum and sulcus. The cingulum is moderately laevorotary and is undivided.
Full tabulation formula: undetermined (?PR, n′, 4–5a, 6+′′, nc, n′′′, n′′′′, ns)
Archaeopyle: formed through the compound loss of one to three anterior intercalary plates.
Dimensions:
Overall length 37 μm (43 μm) 49 μm; maximum width 30 μm (38 μm) 43 μm
20 measured specimens
Remarks:
The ovoidal to biconical shape, very broad cingulum with aligned coarser grana, well-defined posterior sulcal margin and the loss of up to three anterior intercalary plates in Heibergella? obelixii sp. nov. invites comparison to Rhaetogonyaulax nagelii sp. nov. And Rhaetogonyaulax wigginsii. However, as there is no suggestion of further plate loss in archaeopyle formation, and the epicyst is conate rather than forming a true apical horn, this new species is questionably placed in Heibergella herein.
Affinities/Comparison:
Heibergella? obelixii sp. nov. is smaller than all previously published species of this genus, and it has a notably broader cingulum which is reminiscent of Rhaetogonyaulax. It differs further from the type species, Heibergella asymmetrica Bujak and Fisher, 1976, in possessing a coarsely granulate autophragm and lacking a pronounced apical horn. The other species of Heibergella described by Bujak and Fisher (1976) from the Canadian Arctic, i.e., Heibergella aculeata and Heibergella salebrosacea, are strongly biconical with longer apical horns and have short, acuminate antapical horns. Thus, these differ substantially from the hemispherical to flat-based antapex of Heibergella? obelixii sp. nov. The dense covering of spines and the frequent second antapical horn further distinguish Heibergella aculeata. Although Morbey (1975, pl. 14, fig. 2) considered Rhombodella kendelbachia to have an apical archaeopyle, the author appears to have illustrated a specimen with mechanical damage around the apex. Thus, this taxon was transferred to Heibergella by Lentin and Williams (1981). Heibergella kendelbachia is distinguished from Heibergella? obelixii sp. nov., by its more strongly rhomboidal outline, with a far less pronounced cingulum or sulcus. It differs further in occasionally possessing short (up to 2 μm) processes that are “tapered, cylindrical” and with “slender hair-like stems and simple or bifurcate terminations.” However, these processes are also not readily discernable in the type material (Morbey, 1975, pl. 14, figs. 1–4, pl. 17, figs. 1–3).