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Rhynchodiniopsis echinatus
Plate 12, Figs. 10, 12, 13, 15, 16, Plate 13, Figs. 1, 2
Holotype: Plate 12, Figures 12, 15
Paratype: Plate 12, Figure 10
Type Locality: Speeton Bed C7C, early Hauterivian, inversum ammonite Zone. Holotype: Slide Lr.C7C(1). E.F. S32.4.
Paratype: Slide C6(2). E.F. F46.3.
Derivation of Name: From the Latin echinatus, spiny, pricklyin reference to the prominent gonal spines of this species.
Diagnosis: A large, ovoidal gonyaulacacean dinocyst species with a low, rounded apical protrusion capped by a feathered structure with a small coronate termination. The cyst surface ranges from smooth to lightly scabrate, occasionally with some low, localised microreticulation. Tabulation of the formula 4', 6", ?c, 6"', 1p, 1p.v., 1"" is outlined by low sutural crests bearing regular, simple acuminate spines. Gonal areas bear spinose extensions significantly exceeding the normal crestal height. The archeopyle is single plate precingular, formed by detachment of plate 3".
Dimensions: Holotype: 104 × 111 μm. Cingular spines: 15 μm
Paratype (oblique polar orientation): 116 × 104 μm. Cingular
spines: 15 μm
Overall: 132 (115) 94 μm × 144 (118) 96 μm. Cingular spines:
20 (15) 13μm.
Specimens Measured: 12
Remarks: This species is reminiscent of several others, notably Rhynchodiniopsis ingens Duxbury 2018, Rhynchodiniopsis anglese (Zahiri 1981) Duxbury 2018 and Rhynchodiniopsis martonensis Bailey et al. 1997. It differs from the first two in lacking high, complex cingular crests. In addition, RhynchoRhynchodiniopsis ingens n. sp. is much larger than R. anglese and R. martonensis, and furcate antapical spines and coarsely granular body ornament appear to be typical of R. anglese (Zahiri 1981, p. 15).
In possessing gonal spines significantly higher than the general crest height, R. echinatus n. sp. is similar to Rhynchodiniopsis martonensis Bailey et al. 1997, although the latter species is smaller and has a much more prominent apical projection. Bailey et al. (op. cit., p. 239) stated that R. martonense possesses long spines, “linked by complex trabeculae”. No such features were observed in R. echinatus. The LAD of R. martonensis is middle Volgian (Duxbury et al. 1999 - as R. “machaera”).
Rhynchodiniopsis echinatus n. sp. occurs consistently only between Speeton Beds C7C and C6 (across the early/late Hauterivian boundary, inversum to speetonensis ammonite Zones), with rare, isolated occurrences down to the top of Bed C8B (early Hauterivian, upper regale Zone). Some variation in size was noted within this range, with specimens recovered from the base of the late Hauterivian (Speeton Bed C6) being notably larger than those below.
The presence of this species, often common, is a valuable correlative feature in the UKCS Central North Sea close to the early/late Hauterivian boundary, and it was prominent at that level in wells 14/19-21 and 14/19-E5Y here (text-figs. 11, 12).
Holotype: Plate 12, Figures 12, 15
Paratype: Plate 12, Figure 10
Type Locality: Speeton Bed C7C, early Hauterivian, inversum ammonite Zone. Holotype: Slide Lr.C7C(1). E.F. S32.4.
Paratype: Slide C6(2). E.F. F46.3.
Derivation of Name: From the Latin echinatus, spiny, pricklyin reference to the prominent gonal spines of this species.
Diagnosis: A large, ovoidal gonyaulacacean dinocyst species with a low, rounded apical protrusion capped by a feathered structure with a small coronate termination. The cyst surface ranges from smooth to lightly scabrate, occasionally with some low, localised microreticulation. Tabulation of the formula 4', 6", ?c, 6"', 1p, 1p.v., 1"" is outlined by low sutural crests bearing regular, simple acuminate spines. Gonal areas bear spinose extensions significantly exceeding the normal crestal height. The archeopyle is single plate precingular, formed by detachment of plate 3".
Dimensions: Holotype: 104 × 111 μm. Cingular spines: 15 μm
Paratype (oblique polar orientation): 116 × 104 μm. Cingular
spines: 15 μm
Overall: 132 (115) 94 μm × 144 (118) 96 μm. Cingular spines:
20 (15) 13μm.
Specimens Measured: 12
Remarks: This species is reminiscent of several others, notably Rhynchodiniopsis ingens Duxbury 2018, Rhynchodiniopsis anglese (Zahiri 1981) Duxbury 2018 and Rhynchodiniopsis martonensis Bailey et al. 1997. It differs from the first two in lacking high, complex cingular crests. In addition, RhynchoRhynchodiniopsis ingens n. sp. is much larger than R. anglese and R. martonensis, and furcate antapical spines and coarsely granular body ornament appear to be typical of R. anglese (Zahiri 1981, p. 15).
In possessing gonal spines significantly higher than the general crest height, R. echinatus n. sp. is similar to Rhynchodiniopsis martonensis Bailey et al. 1997, although the latter species is smaller and has a much more prominent apical projection. Bailey et al. (op. cit., p. 239) stated that R. martonense possesses long spines, “linked by complex trabeculae”. No such features were observed in R. echinatus. The LAD of R. martonensis is middle Volgian (Duxbury et al. 1999 - as R. “machaera”).
Rhynchodiniopsis echinatus n. sp. occurs consistently only between Speeton Beds C7C and C6 (across the early/late Hauterivian boundary, inversum to speetonensis ammonite Zones), with rare, isolated occurrences down to the top of Bed C8B (early Hauterivian, upper regale Zone). Some variation in size was noted within this range, with specimens recovered from the base of the late Hauterivian (Speeton Bed C6) being notably larger than those below.
The presence of this species, often common, is a valuable correlative feature in the UKCS Central North Sea close to the early/late Hauterivian boundary, and it was prominent at that level in wells 14/19-21 and 14/19-E5Y here (text-figs. 11, 12).