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Chatangiella islae
Chatangiella islae, Pearce, M. A. et al. 2019
Holotype: Pearce, M. A. et al. 2019, Plate I, 1–3
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Original description: [Pearce, M. A. et al. 2019]:
Diagnosis:
A species of Chatangiella with a granular endophragm and a periphragm possessing spines on the anterior and posterior margin of the cingulum only.
Description:
Intermediate-sized, bicavate, deflandreoid peridinioid cyst.
The cyst wall is two-layered composed of a finely to moderately granular endophragm (1 μm thick) and a smooth to finely granular periphragm (~0.5 μm thick) that possesses spines on the anterior and posterior margin of the cingulum only. The spines are typically 4 μm in length (varying between and within specimens), rounded,pointed or minutely bifurcating distally and may be connected at the base to 2 or 3 other spines. The spines are hollow or appear to be solid when they are particularly thin and delineates a pentapartite cingulum.
The pericyst is ventrodorsally compressed, longitudinally elongate, forming a short and blunt apical horn, two antapical horns (right antapical horn shorter), and a bulge around the cingulum. Below the apical horn, the epipericyst typically lacks ‘shoulders’ and the ambital outline is typically slightly convex to the cingulum. Occasionally, specimens with moderately well-developed rounded to sub-angular shoulders are present. The hypopericyst is straight to tapering posteriorly.
The endocyst is typically rounded, appressed to the lateral margin of the periphragm, resulting in a bicavation. Circumcavate forms have not been observed.
The tabulation is defined by the nature of the archaeopyle and pentapartite cingulum, and the formula is presumably peridinioid.
The parasulcus is not obvious.
The endoarchaeopyle is Type I 2a , the periarchaeopyle is typically Type I 2a , iso-deltaform to isothetaform, and the perioperculum is detached.
Rare specimens have been observed with well-developed ‘shoulders’ and an iso-omegaform periarchaeopyle. These are included in Chatangiella islae sp. nov., but are considered atypical.
Dimensions:
Endocyst (width × length): 36(45.7)56 μm × 39(47.1)57 μm, pericyst length 67(83.2)98 μm (Fig. 3), maximum spine length 1(3.6)5 μm.
Number of specimens measured: 23
Remarks:
Chatangiella islae sp. nov. is known to occur in high relative numbers in the mid-Upper Cretaceous of the Norwegian–Greenland Sea, typically reaching over 20% of the entire assemblage (Radmacher et al. (2015) state that C. islae sp. nov. (as Chatangiella “spinosa”) is common to abundant at the base of their Dinoptergyium alatum Zone that has a range of? intra Early Coniacian to Santonian. This species is well known to biostratigraphers working on material from the North Sea and Norwegian–Greenland seas, and has been reported under various informal names including Chatangiella “cingulispinosa” or C. “spinosa”.
Affinities:
Chatangiella islae sp. nov. differs from all other species of Chatangiella by possessing spines restricted to the anterior and posterior margin of the cingulum. It most closely resembles Chatangiella eminens (Pearce, 2010) that differs by possessing intratabular spines on the precingular and postcingular plates. The cingular spines in C. eminens are also broader-based.
Holotype: Pearce, M. A. et al. 2019, Plate I, 1–3
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Pearce, M. A. et al. 2019]:
Diagnosis:
A species of Chatangiella with a granular endophragm and a periphragm possessing spines on the anterior and posterior margin of the cingulum only.
Description:
Intermediate-sized, bicavate, deflandreoid peridinioid cyst.
The cyst wall is two-layered composed of a finely to moderately granular endophragm (1 μm thick) and a smooth to finely granular periphragm (~0.5 μm thick) that possesses spines on the anterior and posterior margin of the cingulum only. The spines are typically 4 μm in length (varying between and within specimens), rounded,pointed or minutely bifurcating distally and may be connected at the base to 2 or 3 other spines. The spines are hollow or appear to be solid when they are particularly thin and delineates a pentapartite cingulum.
The pericyst is ventrodorsally compressed, longitudinally elongate, forming a short and blunt apical horn, two antapical horns (right antapical horn shorter), and a bulge around the cingulum. Below the apical horn, the epipericyst typically lacks ‘shoulders’ and the ambital outline is typically slightly convex to the cingulum. Occasionally, specimens with moderately well-developed rounded to sub-angular shoulders are present. The hypopericyst is straight to tapering posteriorly.
The endocyst is typically rounded, appressed to the lateral margin of the periphragm, resulting in a bicavation. Circumcavate forms have not been observed.
The tabulation is defined by the nature of the archaeopyle and pentapartite cingulum, and the formula is presumably peridinioid.
The parasulcus is not obvious.
The endoarchaeopyle is Type I 2a , the periarchaeopyle is typically Type I 2a , iso-deltaform to isothetaform, and the perioperculum is detached.
Rare specimens have been observed with well-developed ‘shoulders’ and an iso-omegaform periarchaeopyle. These are included in Chatangiella islae sp. nov., but are considered atypical.
Dimensions:
Endocyst (width × length): 36(45.7)56 μm × 39(47.1)57 μm, pericyst length 67(83.2)98 μm (Fig. 3), maximum spine length 1(3.6)5 μm.
Number of specimens measured: 23
Remarks:
Chatangiella islae sp. nov. is known to occur in high relative numbers in the mid-Upper Cretaceous of the Norwegian–Greenland Sea, typically reaching over 20% of the entire assemblage (Radmacher et al. (2015) state that C. islae sp. nov. (as Chatangiella “spinosa”) is common to abundant at the base of their Dinoptergyium alatum Zone that has a range of? intra Early Coniacian to Santonian. This species is well known to biostratigraphers working on material from the North Sea and Norwegian–Greenland seas, and has been reported under various informal names including Chatangiella “cingulispinosa” or C. “spinosa”.
Affinities:
Chatangiella islae sp. nov. differs from all other species of Chatangiella by possessing spines restricted to the anterior and posterior margin of the cingulum. It most closely resembles Chatangiella eminens (Pearce, 2010) that differs by possessing intratabular spines on the precingular and postcingular plates. The cingular spines in C. eminens are also broader-based.