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Nematosphaeropsis compositus
From Fensome et al., 2019:
Nematosphaeropsis compositus Duxbury, 2018, p.187–188, pl.1, figs.,7,11,19; pl.2, fig.1. Holotype: Duxbury, 2018, pl.1, figs.7,11. Age: late Valanginian.
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Original description Duxbury, 2018:
Plate 1, figures 7, 11, 19, Plate 2, figure 1
Holotype: Plate 1, Figures 7, 11.
Paratype: Plate 1, Figure 19.
Type Locality: Holotype, well 20/01-10Z at 9029.40 ft (conventional
core chip), upper Valanginian. Paratype, well 20/01-11Z
at 9324.60 ft, upper Valanginian. Holotype: E.F S37.0.
Paratype E.F. F68.2.
Derivation of Name: From the Latin compositus, orderly, regular, well-arranged – in reference to the sutural crests.
Diagnosis: A small, robust, spheroidal dinoflagellate cyst with a reflected tabulation pattern typical for the genus. The cyst is smooth and surmounted by a small, solid apical projection. Short, regularly-spaced gonal and sutural spines are distally connected by delicate trabeculae, forming low fenestrate crests. The archeopyle is precingular, involving the displacement of plate 3".
Dimensions: Holotype: Length – 53 μm. Width – 51 μm.
Paratype: Length – 53 μm. Width – 51 μm.
Overall: Length – 58 (51) 43 μm. Width – 56 (49) 43 μm.
Specimens Measured: 10.
Remarks: Nematosphaeropsis compositus n. sp. is a distinctivespecies possessing low, fenestrate crests. It has been referred to in various industry reports and in Davey (2001) as Nematosphaeropsis “pseudoscala”, although there is little resemblance to the much larger Nematosphaeropsis scala Duxbury 1977. The latter species possesses much longer gonal and sutural processes surmounted by a less-regular, often fragmented distal trabecular network.
The FAD of N. compositus n. sp. at Speeton is within the lower Valanginian, Bed D3E, immediately above the FAD in Unit D4B of Spiniferites spp., including Spiniferites primaevus (Duxbury 1977) Monteil 1991 and S. twistringiensis (Maier 1959) Fensome et al. 1990; it is very similar to the latter but differs in possessing trabeculae. This is a much earlier FAD than the lower Hauterivian level, upper Bed C8B at Speeton, which was suggested by Davey (2001, Figure 1). The closeness of Nematosphaeropsis compositus n. sp. to species of Spiniferites, particularly S. twistringiensis and its position within the Subfamily Gonyaulacoideae (Fensome et al. 1993, p. 92) are supported by the S-type ventral organisation. However, although Fensome et al. described three or four climactal plates for that subfamily, they state that the fourth apical plate is reduced or absent. In the current study, Nematosphaeropsis compositus n. sp. appears to possess four climactal plates, but it is plate 1' (Kofoid notation) which is much reduced; this is particularly well-demonstrated by the specimen figured here in Plate 2, Figure 1.
Nematosphaeropsis compositus Duxbury, 2018, p.187–188, pl.1, figs.,7,11,19; pl.2, fig.1. Holotype: Duxbury, 2018, pl.1, figs.7,11. Age: late Valanginian.
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Original description Duxbury, 2018:
Plate 1, figures 7, 11, 19, Plate 2, figure 1
Holotype: Plate 1, Figures 7, 11.
Paratype: Plate 1, Figure 19.
Type Locality: Holotype, well 20/01-10Z at 9029.40 ft (conventional
core chip), upper Valanginian. Paratype, well 20/01-11Z
at 9324.60 ft, upper Valanginian. Holotype: E.F S37.0.
Paratype E.F. F68.2.
Derivation of Name: From the Latin compositus, orderly, regular, well-arranged – in reference to the sutural crests.
Diagnosis: A small, robust, spheroidal dinoflagellate cyst with a reflected tabulation pattern typical for the genus. The cyst is smooth and surmounted by a small, solid apical projection. Short, regularly-spaced gonal and sutural spines are distally connected by delicate trabeculae, forming low fenestrate crests. The archeopyle is precingular, involving the displacement of plate 3".
Dimensions: Holotype: Length – 53 μm. Width – 51 μm.
Paratype: Length – 53 μm. Width – 51 μm.
Overall: Length – 58 (51) 43 μm. Width – 56 (49) 43 μm.
Specimens Measured: 10.
Remarks: Nematosphaeropsis compositus n. sp. is a distinctivespecies possessing low, fenestrate crests. It has been referred to in various industry reports and in Davey (2001) as Nematosphaeropsis “pseudoscala”, although there is little resemblance to the much larger Nematosphaeropsis scala Duxbury 1977. The latter species possesses much longer gonal and sutural processes surmounted by a less-regular, often fragmented distal trabecular network.
The FAD of N. compositus n. sp. at Speeton is within the lower Valanginian, Bed D3E, immediately above the FAD in Unit D4B of Spiniferites spp., including Spiniferites primaevus (Duxbury 1977) Monteil 1991 and S. twistringiensis (Maier 1959) Fensome et al. 1990; it is very similar to the latter but differs in possessing trabeculae. This is a much earlier FAD than the lower Hauterivian level, upper Bed C8B at Speeton, which was suggested by Davey (2001, Figure 1). The closeness of Nematosphaeropsis compositus n. sp. to species of Spiniferites, particularly S. twistringiensis and its position within the Subfamily Gonyaulacoideae (Fensome et al. 1993, p. 92) are supported by the S-type ventral organisation. However, although Fensome et al. described three or four climactal plates for that subfamily, they state that the fourth apical plate is reduced or absent. In the current study, Nematosphaeropsis compositus n. sp. appears to possess four climactal plates, but it is plate 1' (Kofoid notation) which is much reduced; this is particularly well-demonstrated by the specimen figured here in Plate 2, Figure 1.