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Exiguisphaera asketa
From Fensome et al., 2019:
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Original description Duxbury, 2018:
Holotype: Plate 1, Figures 2, 3.
Paratype: Plate 5, Figures 14, 15.
Type Locality: Division D4D, base Valanginian, Speeton Clay, Speeton, England Holotype: E.F. G33.2. Paratype: E. F. B37.3
Derivation of Name: From the Greek asketos, curiously wrought, ornamented – in reference to the surface ornament.
Diagnosis: Asmall, fairly robust, spheroidal dinoflagellate cyst with a reflected tabulation pattern of ?a.cl., 4', 6", ?c, 6''', 1p, 1p.v., 1''''. Plates are outlined by fenestrate crests, low but of variable complexity; the fenestration tends to be finer along distal crest margins. Often dense, intratabular surface ornament in the form of short, solid spines is present, ranging from discrete to variously-connected elements or a low reticulum. The archeopyle is precingular, involving the displacement of plates 3" and 4".
Dimensions: Holotype: Length – 51 μm. Width – 53 μm.
Paratype: Length – 68 μm. Width – 63 μm.
Overall: Length – 68 (57) 48 μm. Width – 63 (55) 48 μm.
Specimens Measured: 15.
Remarks: Exiguisphaera asketa n. sp. differs from other species of this genus in possessing often dense intratabular ornament and crests which are low but variously fenestrate, with the fenestrations tending to be finer along crestal margins. It is intermediate in size between Exiguisphaera phragma Duxbury 1979a and E. plectilis Duxbury 1980. It is more robust than the former with significantly more surface ornament and higher, more complex sutural crests, and it is smaller, thinner-walled and significantly less ornate than the latter. Specimens illustrated from the Valanginian of the Speeton Clay (horizon unspecified) by Jan du Chene et al. (1986, Plate 29, Figures 1–4) are considered sufficiently ornate to be included here.
The common occurrence of this very distinctive species is restricted to a short interval across the Berriasian/Valanginian boundary, Beds D6C to D4C at Speeton, peaking within Bed D4D, at the base of the Valanginian. It has been observed rarely as old as the upper part of Bed D6I (Figure 2).
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Original description Duxbury, 2018:
Holotype: Plate 1, Figures 2, 3.
Paratype: Plate 5, Figures 14, 15.
Type Locality: Division D4D, base Valanginian, Speeton Clay, Speeton, England Holotype: E.F. G33.2. Paratype: E. F. B37.3
Derivation of Name: From the Greek asketos, curiously wrought, ornamented – in reference to the surface ornament.
Diagnosis: Asmall, fairly robust, spheroidal dinoflagellate cyst with a reflected tabulation pattern of ?a.cl., 4', 6", ?c, 6''', 1p, 1p.v., 1''''. Plates are outlined by fenestrate crests, low but of variable complexity; the fenestration tends to be finer along distal crest margins. Often dense, intratabular surface ornament in the form of short, solid spines is present, ranging from discrete to variously-connected elements or a low reticulum. The archeopyle is precingular, involving the displacement of plates 3" and 4".
Dimensions: Holotype: Length – 51 μm. Width – 53 μm.
Paratype: Length – 68 μm. Width – 63 μm.
Overall: Length – 68 (57) 48 μm. Width – 63 (55) 48 μm.
Specimens Measured: 15.
Remarks: Exiguisphaera asketa n. sp. differs from other species of this genus in possessing often dense intratabular ornament and crests which are low but variously fenestrate, with the fenestrations tending to be finer along crestal margins. It is intermediate in size between Exiguisphaera phragma Duxbury 1979a and E. plectilis Duxbury 1980. It is more robust than the former with significantly more surface ornament and higher, more complex sutural crests, and it is smaller, thinner-walled and significantly less ornate than the latter. Specimens illustrated from the Valanginian of the Speeton Clay (horizon unspecified) by Jan du Chene et al. (1986, Plate 29, Figures 1–4) are considered sufficiently ornate to be included here.
The common occurrence of this very distinctive species is restricted to a short interval across the Berriasian/Valanginian boundary, Beds D6C to D4C at Speeton, peaking within Bed D4D, at the base of the Valanginian. It has been observed rarely as old as the upper part of Bed D6I (Figure 2).