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Tenua scabrosa
From Fensome et al., 2019:
Tenua scabrosa (Cookson and Eisenack, 1970a, p.146, pl.13, figs.6–7) Fensome et al., 2019a, p.49.
Holotype: Cookson and Eisenack, 1970a, pl.13, fig.6; Fensome et al., 2019a, fig.18L.
Originally Canningia, sunsequently (and now) Tenua Eisenack.
Taxonomic junior synonyms: Canningia aspera and Circulodinium cingulatum, both according to Fensome et al. (2019a, p.49).
Age: Albian–Cenomanian.
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Original description: [Cookson and Eisenack, 1970, p.146]:
Description:
Shell rather flat, almost circular to slightly angular in outline, with a slight apical prominence and with, as in the holotype, or without a slight antapical concavity bounded by blunt or pointed outgrowths. In one example (from 1486-1523 ft) a girdle is clearly evident on the ventral surface. The shell opens by the removal of a considerable portion of the epitheca. The ornamentation consists of densely arranged, irregularly outlined thickenings, some of which narrow to short, hair-like appendages (Pl. 13, fig. 4).
Dimensions:
Holotype: c. 102 µm long, 90 µm broad.
Range in breadth: c. 78-94 µm.
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Comments Fensome et al., 2019a:
Cookson & Eisenack (1970, p. 146) described the ornamentation of Canningia scabrosa (misspelled in the protologue as “scabrose”) as consisting of “… densely arranged, irregularly outlined thickenings, some of which narrow to [form] short, hair-like appendages...”. As the wall structure is clearly not holocavate and the ornamentation is apparently free-standing and covers the entire cyst surface, we transfer this species to Tenua. The ornament is so similar to that of Canningia? aspera that we consider the two species to be synonymous. Canningia? aspera was erected by Singh (1971, p. 322) for large (average 97 x 100 μm) areoligeracean cysts. According to Singh, the 2.5 μm-thick wall is ornamented by “… thick, irregular-shaped elevations surmounted by 2–4-micron long, conical spines.”
Specimens attributable to Tenua scabrosa are common in upper Lower Cretaceous material from Axel Heiberg Island, arctic Canada. In the arctic material, the wall is not as thick as Singh reported from Alberta, and the spines range from 2–8 μm in length. The dorsoventral area is darker than other parts of the cyst on some specimens, suggesting a wall thickening in that region.
He Chengquan et al (1999) diagnosed Circulodinium cingulatum in part as follows: “Autophragm … surface ornamented with rarely free processes of varying length and size, most of them shorter, verrucous to bluntly denticulate, 0.5 – 1.0 μm long, fewer processes shortly baculate (up to 3.5 μm long) with blunt unwidened tips.”
From the protologue illustrations, the processes appear to be short, isolated and broad based, as is the case for Tenua scabrosa. He Chengquan et al. (1999) differentiated Circulodinium cingulatum from Tenua (then Circulodinium) attadalica on the basis of the presence of paracingular ridges on the former. However, we consider the species of He Chengquan et al. (1999) to be akin to Tenua scabrosa rather than Tenua attadalica, and the presence or absence of a defined paracingulum to be an intraspecific variation.
Stratigraphical occurrence. Cookson & Eisenack (1970) recorded Tenua (as Canningia) scabrosa from the Albian to Cenomanian of Australia. Singh (1971) described Tenua (as Canningia) aspera from the Albian of Alberta, Canada. The type material of Circulodinium cingulatum is from the upper Hauterivian to Barremian of China.
Tenua scabrosa (Cookson and Eisenack, 1970a, p.146, pl.13, figs.6–7) Fensome et al., 2019a, p.49.
Holotype: Cookson and Eisenack, 1970a, pl.13, fig.6; Fensome et al., 2019a, fig.18L.
Originally Canningia, sunsequently (and now) Tenua Eisenack.
Taxonomic junior synonyms: Canningia aspera and Circulodinium cingulatum, both according to Fensome et al. (2019a, p.49).
Age: Albian–Cenomanian.
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Original description: [Cookson and Eisenack, 1970, p.146]:
Description:
Shell rather flat, almost circular to slightly angular in outline, with a slight apical prominence and with, as in the holotype, or without a slight antapical concavity bounded by blunt or pointed outgrowths. In one example (from 1486-1523 ft) a girdle is clearly evident on the ventral surface. The shell opens by the removal of a considerable portion of the epitheca. The ornamentation consists of densely arranged, irregularly outlined thickenings, some of which narrow to short, hair-like appendages (Pl. 13, fig. 4).
Dimensions:
Holotype: c. 102 µm long, 90 µm broad.
Range in breadth: c. 78-94 µm.
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Comments Fensome et al., 2019a:
Cookson & Eisenack (1970, p. 146) described the ornamentation of Canningia scabrosa (misspelled in the protologue as “scabrose”) as consisting of “… densely arranged, irregularly outlined thickenings, some of which narrow to [form] short, hair-like appendages...”. As the wall structure is clearly not holocavate and the ornamentation is apparently free-standing and covers the entire cyst surface, we transfer this species to Tenua. The ornament is so similar to that of Canningia? aspera that we consider the two species to be synonymous. Canningia? aspera was erected by Singh (1971, p. 322) for large (average 97 x 100 μm) areoligeracean cysts. According to Singh, the 2.5 μm-thick wall is ornamented by “… thick, irregular-shaped elevations surmounted by 2–4-micron long, conical spines.”
Specimens attributable to Tenua scabrosa are common in upper Lower Cretaceous material from Axel Heiberg Island, arctic Canada. In the arctic material, the wall is not as thick as Singh reported from Alberta, and the spines range from 2–8 μm in length. The dorsoventral area is darker than other parts of the cyst on some specimens, suggesting a wall thickening in that region.
He Chengquan et al (1999) diagnosed Circulodinium cingulatum in part as follows: “Autophragm … surface ornamented with rarely free processes of varying length and size, most of them shorter, verrucous to bluntly denticulate, 0.5 – 1.0 μm long, fewer processes shortly baculate (up to 3.5 μm long) with blunt unwidened tips.”
From the protologue illustrations, the processes appear to be short, isolated and broad based, as is the case for Tenua scabrosa. He Chengquan et al. (1999) differentiated Circulodinium cingulatum from Tenua (then Circulodinium) attadalica on the basis of the presence of paracingular ridges on the former. However, we consider the species of He Chengquan et al. (1999) to be akin to Tenua scabrosa rather than Tenua attadalica, and the presence or absence of a defined paracingulum to be an intraspecific variation.
Stratigraphical occurrence. Cookson & Eisenack (1970) recorded Tenua (as Canningia) scabrosa from the Albian to Cenomanian of Australia. Singh (1971) described Tenua (as Canningia) aspera from the Albian of Alberta, Canada. The type material of Circulodinium cingulatum is from the upper Hauterivian to Barremian of China.