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Aptea cassis
From Fensome et al., 2019:
Aptea cassis, Fensome et al., 2019a, p.13–15, figs.4A–N.
Holotype: Fensome et al., 2019a, fig.4C. NIA.
Age: latest Albian to early Cenomanian.
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Holotype from the lowermost Slater River Formation (uppermost Albian or lower Cenomanian), Hume River section, Northwest Territories, Canada. Sample 07-Peel-43, 724.5 m from base of section, slide 5262-012C, coordinates 190 × 0909, England Finder T33-2; GSC type number 139874, curated in the National Collection of Type Invertebrate and Plant Fossils, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8. At the time of writing, this specimen was on long-term loan to GSC Atlantic, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2. See also Appendix 3 herein and Fensome (2016) for further details.
Derivation of name. From the Latin cassis, meaning hunting net or snare, in reference to the reticulate nature of the ornament. The epithet is a noun in apposition.
Diagnosis. A species of Aptea with a coarse reticulum formed of simple low membranous crests; there are no free-standing elements. The reticulum is distributed across the dorsal and ventral surfaces, although it may be somewhat more weakly developed in mid-ventral and mid-dorsal areas. The antapex is symmetrical or asymmetrical, with developments of two usually unequal antapical protuberances or horns.
Dimensions. Overall width 62 (71) 80 μm (range of 13 specimens); overall length (operculum in place) 77 (83) 90 μm (range of four specimens); overall length (operculum absent) 60 (70) 81 μm (range of eight specimens). Holotype: Overall width 62 μm; overall length (operculum in place) 77 μm.
Comments. This species is characterised by a simple network of low crests; no additional convoluted or free-standing elements occur. The ornament of Aptea polymorpha tends to be higher and more convoluted. Aptea cassis also resembles Cyclonephelium compactum, but the latter has distinct dorsoventral areas devoid of ornament and higher and generally more convoluted muri. Extreme variants have a bulging lateral protuberance formed by the endophragm, but otherwise clearly belong to this species.
Stratigraphical occurrence. Aptea cassis occurs in the lowermost part of the Slater River Formation on the Mackenzie Plain, previously dated as early Cenomanian in age based on rare ammonites, fish scales and lithostratigraphical correlation, but dated by Fensome (Citation2016) as latest Albian based on dinoflagellate cysts.
Aptea cassis, Fensome et al., 2019a, p.13–15, figs.4A–N.
Holotype: Fensome et al., 2019a, fig.4C. NIA.
Age: latest Albian to early Cenomanian.
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Holotype from the lowermost Slater River Formation (uppermost Albian or lower Cenomanian), Hume River section, Northwest Territories, Canada. Sample 07-Peel-43, 724.5 m from base of section, slide 5262-012C, coordinates 190 × 0909, England Finder T33-2; GSC type number 139874, curated in the National Collection of Type Invertebrate and Plant Fossils, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A 0E8. At the time of writing, this specimen was on long-term loan to GSC Atlantic, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada B2Y 4A2. See also Appendix 3 herein and Fensome (2016) for further details.
Derivation of name. From the Latin cassis, meaning hunting net or snare, in reference to the reticulate nature of the ornament. The epithet is a noun in apposition.
Diagnosis. A species of Aptea with a coarse reticulum formed of simple low membranous crests; there are no free-standing elements. The reticulum is distributed across the dorsal and ventral surfaces, although it may be somewhat more weakly developed in mid-ventral and mid-dorsal areas. The antapex is symmetrical or asymmetrical, with developments of two usually unequal antapical protuberances or horns.
Dimensions. Overall width 62 (71) 80 μm (range of 13 specimens); overall length (operculum in place) 77 (83) 90 μm (range of four specimens); overall length (operculum absent) 60 (70) 81 μm (range of eight specimens). Holotype: Overall width 62 μm; overall length (operculum in place) 77 μm.
Comments. This species is characterised by a simple network of low crests; no additional convoluted or free-standing elements occur. The ornament of Aptea polymorpha tends to be higher and more convoluted. Aptea cassis also resembles Cyclonephelium compactum, but the latter has distinct dorsoventral areas devoid of ornament and higher and generally more convoluted muri. Extreme variants have a bulging lateral protuberance formed by the endophragm, but otherwise clearly belong to this species.
Stratigraphical occurrence. Aptea cassis occurs in the lowermost part of the Slater River Formation on the Mackenzie Plain, previously dated as early Cenomanian in age based on rare ammonites, fish scales and lithostratigraphical correlation, but dated by Fensome (Citation2016) as latest Albian based on dinoflagellate cysts.