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Meiourogonyaulax stoveri ssp. grandis
From Fensome et al., 2019:
Meiourogonyaulax stoveri ssp. grandis Duxbury, 2019, p.196–197, pl.17, figs.6,9,12. Holotype: Duxbury, 2019, pl.17, fig.6. Age:
early Aptian.
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Original description Duxbury, 2019:
Plate 17, Figures 6, 9, 12
Holotype: Plate 17, Figure 6.
Paratype: Plate 17, Figures 9, 12.
Type Locality: Heslerton No. 2 (core chips). Holotype at 13.20 m, early Aptian age, E.F. P51.3, Paratype at 12.20 m, early Aptian age, E.F. L39.0.
Derivation of Name: From the Latin grandis, great - in reference to the very large size of this subspecies.
Diagnosis: A very large, thick-walled dinoflagellate cyst, subcircular to pentagonal in outline with fairly coarse reticulate ornament typically confined to penitabular areas. Tabulation of the formula ?', 6'', ?c, 6''', 1p, 1p.v., 1'''' is marked by distally entire crests which are higher on the hypocyst and particularly prominent towards the antapex, giving the cyst an angular outline. The sulcus broadens antapically and has a deep central groove. The archeopyle is apical and the zig-zag archeopyle margin displays a distinct but shallow sulcal notch.
Dimensions: Holotype: Length - 84 μm. Width - 91 μm.
Paratype: Length - 73 μm. Width - 84 μm.
Complete specimen (2 recorded): 99 (96) 94 μm × 96 (96) 96 μm.
Overall (operculum lost): Length - 94 (78) 63 μm; Width - 104 (90) 78 μm.
Specimens Measured: 16.
Remarks: This subspecies is typical of the species in its often subcircular outline, thick wall, crests which are highest towards the antapex and sulcus broadening antapically. However, it differs in its significantly greater size (complete specimens about 20% larger than Millioud’s type material) and in the coarseness of its reticulate ornament, which can cover plates but which tends to be concentrated in penitabular areas, leaving conspicuous “bald” areas. Some suturocavation can be observed, with the crestal membrane distinctly perforate. Meiourogonyaulax stoveri subsp. grandis tends to angularity, often superficially similar to that of Ellipsoidictyum imperfectum subsp. quadrum (compare Plate 17, Figure 6 with Plate 17, Figure 1 and Plate 18, Figures 1, 6, 10).
This subspecies was restricted to the latest Barremian to early Aptian interval in the present study (14.95 m to 12.20 m in Heslerton No. 2), whereas specimens assigned to M. stoveri subsp. stoveri were observed no higher than 17.00 m, where they were rare. Millioud (1969, p. 429) described M. stoveri as, “sporadically present in the Barremian and in the lower
Aptian”.
Meiourogonyaulax stoveri ssp. grandis Duxbury, 2019, p.196–197, pl.17, figs.6,9,12. Holotype: Duxbury, 2019, pl.17, fig.6. Age:
early Aptian.
---------------------------------------------------------------------------------------------------
Original description Duxbury, 2019:
Plate 17, Figures 6, 9, 12
Holotype: Plate 17, Figure 6.
Paratype: Plate 17, Figures 9, 12.
Type Locality: Heslerton No. 2 (core chips). Holotype at 13.20 m, early Aptian age, E.F. P51.3, Paratype at 12.20 m, early Aptian age, E.F. L39.0.
Derivation of Name: From the Latin grandis, great - in reference to the very large size of this subspecies.
Diagnosis: A very large, thick-walled dinoflagellate cyst, subcircular to pentagonal in outline with fairly coarse reticulate ornament typically confined to penitabular areas. Tabulation of the formula ?', 6'', ?c, 6''', 1p, 1p.v., 1'''' is marked by distally entire crests which are higher on the hypocyst and particularly prominent towards the antapex, giving the cyst an angular outline. The sulcus broadens antapically and has a deep central groove. The archeopyle is apical and the zig-zag archeopyle margin displays a distinct but shallow sulcal notch.
Dimensions: Holotype: Length - 84 μm. Width - 91 μm.
Paratype: Length - 73 μm. Width - 84 μm.
Complete specimen (2 recorded): 99 (96) 94 μm × 96 (96) 96 μm.
Overall (operculum lost): Length - 94 (78) 63 μm; Width - 104 (90) 78 μm.
Specimens Measured: 16.
Remarks: This subspecies is typical of the species in its often subcircular outline, thick wall, crests which are highest towards the antapex and sulcus broadening antapically. However, it differs in its significantly greater size (complete specimens about 20% larger than Millioud’s type material) and in the coarseness of its reticulate ornament, which can cover plates but which tends to be concentrated in penitabular areas, leaving conspicuous “bald” areas. Some suturocavation can be observed, with the crestal membrane distinctly perforate. Meiourogonyaulax stoveri subsp. grandis tends to angularity, often superficially similar to that of Ellipsoidictyum imperfectum subsp. quadrum (compare Plate 17, Figure 6 with Plate 17, Figure 1 and Plate 18, Figures 1, 6, 10).
This subspecies was restricted to the latest Barremian to early Aptian interval in the present study (14.95 m to 12.20 m in Heslerton No. 2), whereas specimens assigned to M. stoveri subsp. stoveri were observed no higher than 17.00 m, where they were rare. Millioud (1969, p. 429) described M. stoveri as, “sporadically present in the Barremian and in the lower
Aptian”.