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Rhaetogonyaulax wigginsii subsp. claviger
Rhaetogonyaulax wigginsii subsp. claviger subsp. nov., Mantle et al. 2020, p. 43
Holotype: Mantle et al. 2020, Plate XII, 24
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (latest Carnian – middle Norian)
Original description: Mantle et al. 2020:
Description:
Medium, proximate, biconical dinoflagellate cysts with a short pyramidal apical horn and more elongate, mace-like antapical horn. A second rudimentary hypocystal horn or short protuberance is only very rarely evident, protruding from the adjacent antapical plate.
Wall: autophragm is scabrate to coarsely granulate with numerous short, acuminate to capitate spines (1–4 μm) surmounting the sutures, particularly bordering the cingulum and sulcus.
A further cluster of spines on the antapical horn is particularly characteristic.
Tabulation: indicated by low ridges that are notably thicker along the cingular and sulcal boundaries. These ridges clearly express the strongly laevorotatory nature of the cingulum, which is offset by two-thirds to a full cingular width
Full tabulation formula: unknown, but can be summarised as ?PR, 4+′, 4–5a, 7′′, nc, n′′′, n′′′′, ns
Archaeopyle: formed by the compound loss of 1 to 5 anterior intercalary plates (the commonest type), the loss of a combination of apical and anterior intercalary plates or all the climactal plates.
Dimensions:
Overall length including the apical horn 52 μm (61 μm) 70 μm; maximum width 39 μm (46 μm) 52 μm
10 measured specimens
Remarks:
Most of the species of Rhaetogonyaulax exhibit a wide variety of surface ornament, and this is generally accepted as reasonable for species level variation. The 16 described species of Rhaetogonyaulax have been synonymised into four (Williams et al., 2017). However, Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. is considered to be best classified as a subspecies of Rhaetogonyaulax wigginsii rather than a new species. It differs substantially in surface ornament from the type material of Stover and Helby (1987), but it remains within the original core concept and description of that species. The tabulation formula is likely to be fully consistent with those of Below (1987) and Stover and Helby (1987), however there are differences in how these authors labelled the apical and anterior intercalary plates.
Affinities/Comparison:
Stover and Helby (1987) noted the morphological variability, particularly in the ornamentation of the autophragm, of Rhaetogonyaulax wigginsii in their original description. These authors stated that this species may have “solid, often distally expanded processes (up to 4 μm long, 0.5–1 μm diameter).” However, the specimens illustrated by Stover and Helby (1987) all have notably broader based verrucae and other projections, in marked contrast with the more slender, elongate spines of Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. The type material of Rhaetogonyaulax wigginsii subsp. Wigginsii also exhibit much rounder hypocysts with only vestigial antapical horns. These specimens thus lack the well-developed antapical horn of Rhaetogonyaulax wigginsii subsp. claviger subsp. nov., and the sharply biconical outline of this subspecies. There is much gradation between these end members however, and most of the specimens of Rhaetogonyaulax wigginsii subsp. wigginsii herein (Plate XII, 16–22) have more conical hypocysts and longer antapical horns than the type material. The present material of Rhaetogonyaulax wigginsii subsp. wigginsii also frequently exhibit several short spines close to the antapical horn, but not the cluster of antapical spines typically developed in Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. The strongly developed antapical horn of Rhaetogonyaulax wigginsii subsp. claviger sp. nov. means it is superficially more similar in shape to Rhaetogonyaulax rhaetica. However, Rhaetogonyaulax rhaetica is larger, longer, has a more elongate spindle-shaped ambitus and lacks the concentration of coarser or longer ornament along the cingular and sulcal borders. Rhaetogonyaulax rhaetica is also a more cosmopolitan taxon; it has been recorded from Rhaetian shallow marine sections, particularly carbonates, from the Arctic to Gondwana. There are few published images of Rhaetogonyaulax rhaetica sensu stricto from the Norian (see above). It is possible that the significant morphological variability in Rhaetogonyaulax wigginsii sensu lato outlined herein may account for some of the pre-Rhaetian records of “Rhaetogonyaulax rhaetica.”
Holotype: Mantle et al. 2020, Plate XII, 24
Type locality: Northern Carnarvon Basin
Local stratigraphical range: Late Triassic (latest Carnian – middle Norian)
Original description: Mantle et al. 2020:
Description:
Medium, proximate, biconical dinoflagellate cysts with a short pyramidal apical horn and more elongate, mace-like antapical horn. A second rudimentary hypocystal horn or short protuberance is only very rarely evident, protruding from the adjacent antapical plate.
Wall: autophragm is scabrate to coarsely granulate with numerous short, acuminate to capitate spines (1–4 μm) surmounting the sutures, particularly bordering the cingulum and sulcus.
A further cluster of spines on the antapical horn is particularly characteristic.
Tabulation: indicated by low ridges that are notably thicker along the cingular and sulcal boundaries. These ridges clearly express the strongly laevorotatory nature of the cingulum, which is offset by two-thirds to a full cingular width
Full tabulation formula: unknown, but can be summarised as ?PR, 4+′, 4–5a, 7′′, nc, n′′′, n′′′′, ns
Archaeopyle: formed by the compound loss of 1 to 5 anterior intercalary plates (the commonest type), the loss of a combination of apical and anterior intercalary plates or all the climactal plates.
Dimensions:
Overall length including the apical horn 52 μm (61 μm) 70 μm; maximum width 39 μm (46 μm) 52 μm
10 measured specimens
Remarks:
Most of the species of Rhaetogonyaulax exhibit a wide variety of surface ornament, and this is generally accepted as reasonable for species level variation. The 16 described species of Rhaetogonyaulax have been synonymised into four (Williams et al., 2017). However, Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. is considered to be best classified as a subspecies of Rhaetogonyaulax wigginsii rather than a new species. It differs substantially in surface ornament from the type material of Stover and Helby (1987), but it remains within the original core concept and description of that species. The tabulation formula is likely to be fully consistent with those of Below (1987) and Stover and Helby (1987), however there are differences in how these authors labelled the apical and anterior intercalary plates.
Affinities/Comparison:
Stover and Helby (1987) noted the morphological variability, particularly in the ornamentation of the autophragm, of Rhaetogonyaulax wigginsii in their original description. These authors stated that this species may have “solid, often distally expanded processes (up to 4 μm long, 0.5–1 μm diameter).” However, the specimens illustrated by Stover and Helby (1987) all have notably broader based verrucae and other projections, in marked contrast with the more slender, elongate spines of Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. The type material of Rhaetogonyaulax wigginsii subsp. Wigginsii also exhibit much rounder hypocysts with only vestigial antapical horns. These specimens thus lack the well-developed antapical horn of Rhaetogonyaulax wigginsii subsp. claviger subsp. nov., and the sharply biconical outline of this subspecies. There is much gradation between these end members however, and most of the specimens of Rhaetogonyaulax wigginsii subsp. wigginsii herein (Plate XII, 16–22) have more conical hypocysts and longer antapical horns than the type material. The present material of Rhaetogonyaulax wigginsii subsp. wigginsii also frequently exhibit several short spines close to the antapical horn, but not the cluster of antapical spines typically developed in Rhaetogonyaulax wigginsii subsp. claviger subsp. nov. The strongly developed antapical horn of Rhaetogonyaulax wigginsii subsp. claviger sp. nov. means it is superficially more similar in shape to Rhaetogonyaulax rhaetica. However, Rhaetogonyaulax rhaetica is larger, longer, has a more elongate spindle-shaped ambitus and lacks the concentration of coarser or longer ornament along the cingular and sulcal borders. Rhaetogonyaulax rhaetica is also a more cosmopolitan taxon; it has been recorded from Rhaetian shallow marine sections, particularly carbonates, from the Arctic to Gondwana. There are few published images of Rhaetogonyaulax rhaetica sensu stricto from the Norian (see above). It is possible that the significant morphological variability in Rhaetogonyaulax wigginsii sensu lato outlined herein may account for some of the pre-Rhaetian records of “Rhaetogonyaulax rhaetica.”