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Operculodinium borgerholtense
Operculodinium borgerholtense Louwye, 2001, p.126–127, fig.4, nos.1–12. Emendation: Soliman et al., 2009, p.75.
Questionable assignment: Louwye (2001, p.126).
Holotype: Louwye, 2001, fig.4, nos.1–5; Soliman et al., 2009, pl.1, figs.1–3; pl.2, figs.11–20.
Age: early-middle Miocene.
Original description (Louwye, 2001):
Operculodinium ? borgerholtense nov. sp. Fig. 4
Holotype - Slide B.R.15/P1, England Finder reference H39/3 (Fig. 4, 1-5).
Etymology - Named after the type locality Borgerhout, called 'Borgerholt' in medieval times.
Repository - Collection of the 'Institut Royal des Sciences Naturelles' (Brussels), catalogue number IRScN b3668.
Type locality - Outcrop 'Borgerhout Rivierenhof described by De Meuter et aI. (1976: 13), altitude -1.9 m O.D. (Ostend Datum), Borgerhout, Antwerp Province, Belgium.
Type stratum - Antwerpen Sands, Berchem Formation, Miocene.
Diagnosis - Spherical to ovoid proximochorate cyst ornamented with low, granulate prismatic luxuriae and numerous, long virgae. The distribution of the granules and simple, solid virgae is non-tabular. The virgae are acuminate, capitate or bifurcated. A low septum located at the antapex arises directly from the pedium and forms an irregular polygon. The geometry of this septum conforms to the outline of an antapical plate in a gonyaulacoid sexiform hypocystal pattern. The archeopyle is formed by the release of the third precingular plate. The operculum is free.
Description - Small cyst with a circular to ovoid ambitus. The homogeneous pedium is thin (less than 0.5 µm) and extends into luxuriae consisting of low granules, long virgae and an almost continuous, low antapical septum. The granules are solid with a diameter and a height of less than 1 µm. The solid virgae are circular in cross-section and their width remains even over almost the whole length of the shaft. Distally they taper rapidly towards sinuous acuminate, capitate or bifurcate tips. The virgae arise directly from the solid pedium, and some degree of proximal fusion with adjacent granules or virgae can occasionally be observed. The pedium forms an almost continuous antapical low ridge or septum (height less than 1.5 µm) with a subrectangular outline and rounded angles. The indentation in the six-sided polygon is directed towards the sulcal area. The septum is a reflection of the antapical plate 1'"'. The precingular archeopyle (type P) is large with smooth margins and rounded angles.
Dimensions - Holotype: length central body: 38 µm, equatorial width central body: 35 µm, length virgae: 6-7 µm. Range: length central body: 35 (37) 39 µm, equatorial width central body: 34 (36) 39 µm, length processes: 4 (6.5) 8 µm. Number of specimens measured: 9.
Remarks - Matsuoka et al. (1997), in their emendation of the genus Operculodinium, do not mention the presence of low septa or ridges, reflecting in part or completely a tabulation. Hence, the provisional assignment to the genus Operculodinium.
Comparison - This species is distinguished from all other Operculodinium species by the antapical ornamentation formed by a more or less continuous septum representing the six-sided gonyaulacoid antapical plate. The dimensions and ambitus of Operculodinium ? eirikianum HEAD et al., 1989 are similar. However, the luxuriae of the latter species consists of an irregular microreticulum of undulating muri and finely granulate virgae.
Occurrence - Lower - Middle Miocene (Antwerpen Sands and Zonderschot Sands of the Berchem Formation) of northern Belgium as Operculodinium sp. 1 (Louwye in press, Louwye et al. 2000).
Emended description (Soliman et al., 2009):
Operculodinium sp. 1. Louwye, 2000, tab. 1.
Operculodinium? borgerholtense Louwye, 2001, p. 126, 127, figs. 4.1–4.12; Jiménez-Moreno et al., 2006, pl. 2, figs. 1–5, pl. 9, fig. 7; Soliman, 2006, p. 54–56, pl. 39, figs. 5–22, text-fig. 22; Soliman and Piller, 2007a, p. 411, pl. 1, figs. 6–12.
Emended diagnosis. Small, thin-walled proximochorate cyst with spherical to subspherical central body bearing numerous solid erect processes and lower ornament. Processes nontabular, smooth or with granules, spinules, and short irregular branches. Lower ornament varies from low verrucae to round-topped coni, round-topped bacculae, and clavae. Low bounding septum and more densely ornamented surface demarcate six-sided antapical plate of subrectangular shape. Archeopyle precingular (3'') with well-defined angles, no accessory sutures. Operculum free.
Type locality. ‘Borgerhout Rivierenhof’ outcrop, Borgerhout, Antwerp Province, Belgium; for both holotype and paratype. A full description of the outcrop, lithology and position of the samples is given by De Meuter et al. (1976, p. 13, fig. 18).
Emended description. Central body thin walled (ca. 0.2–0.3 μm), spherical to subspherical in shape, bearing numerous solid processes and lower ornament. Processes and lower ornament nontabular and fairly evenly distributed over cyst, except in antapical area. Central body wall unstructured under LM but three appressed layers distinguishable under SEM: solid smooth thin inner and outer layers (ca. 0.03 μm) and much thicker densely granulate middle layer (Plate 3, fig.11 and inset). Structure continuous with lower ornament and presumably also with processes. Processes erect, narrow, initially of approximately even thickness and straight, tapering and often sinuous distally. Processes may be smooth for entire length but more commonly have granules, spinules, and short irregular branches, particularly along their distal half (as in holotype, but see Text-Figure 3 for full morphological range). Separation between adjacent process bases typically ca. 1.9–3.5 μm. Lower ornament ca. 0.3–0.7 μm in diameter and 0.6–1.0 μm high, conspicuous, varies from low verrucae to roundtopped coni, round-topped narrow bacculae, and occasionally clavae (Plate 3, fig. 7). Elements evenly distributed, typically separated from each other by one to two, or occasionally three times their diameter. Elements may be somewhat more sparsely distributed on specimens with smooth processes. Occasionally some, but never all, elements fused into low discontinuous ridges (Plate 3, figs. 4, 5, 9). At antapex, low (less than 1.5 μm) almost continuous (Plate 2, figs. 1–4) to discontinuous (Plate 3, figs. 2, 3) septum demarcates six-sided antapical plate. Contact with posterior sulcal plate (which overlaps antapical plate) is long and concave; contacts with posterior intercalary and sixth postcingular plates are short; resulting in subrectangular shape of antapical plate (Text-Figure 2). Ornament on antapical plate more densely clustered and irregular than elsewhere, with many adjacent elements fused at base (Plate 3, figs. 2, 3, 13, 14), and central body surface may be finely pitted (diameter, 0.05–0.20 μm) as seen in Plate 3, figs. 3, 14. Archeopyle formed by release of third precingular plate; margin entire, well-defined angles, no accessory sutures (Text-Figure 2). Archeopyle margin may be slightly raised and thickened, as observed under SEM (Plate 3, fig. 1). Operculum free. No other indications of tabulation.
Dimensions. Holotype: central body length, 38 μm, central body equatorial diameter, 35 μm, length of processes, 6–7 μm. Paratype: central body maximum diameter, 36 μm, length of processes, 5–6 μm. Range based on all specimens measured in the present study: central body maximum diameter, 23(32.8)41 μm, length of processes, 2.5(5.6)8.5 μm; 73 specimens measured (Text-Figure 4, Table 1). Average process width, 0.5(0.74)1.1 μm; 12 specimens measured under SEM.
Comparison. Operculodinium? eirikianum Head et al. 1989 emend. Head 1997, described from the Upper Miocene of the Labrador Sea, has a microreticulate central body surface. The marine acritarch Nannobarbophora walldalei Head 1996b, described from the Pliocene of eastern England, has root-like process bases and the vesicle surface has an irregularly scattered granulation unlike the more prominent and orderly distribution of lower ornament in O.? borgerholtense. Nannobarbophora gedlii Head 2003, described from the Lower Miocene of the Norwegian Sea, has hollow processes and a smooth to sparsely ornamented vesicle surface. Operculodinium? eirikianum has a range base in the uppermost Langhian (Louwye et al., 2007) and therefore overlaps stratigraphically with O.? borgerholtense. Nannobarbophora gedlii has a known range of upper Lower to Middle Miocene and also overlaps stratigraphically with O.? borgerholtense, whereas Nannobarbophora walldalei is not known from deposits older than Late Miocene (Head, 2003).
Questionable assignment: Louwye (2001, p.126).
Holotype: Louwye, 2001, fig.4, nos.1–5; Soliman et al., 2009, pl.1, figs.1–3; pl.2, figs.11–20.
Age: early-middle Miocene.
Original description (Louwye, 2001):
Operculodinium ? borgerholtense nov. sp. Fig. 4
Holotype - Slide B.R.15/P1, England Finder reference H39/3 (Fig. 4, 1-5).
Etymology - Named after the type locality Borgerhout, called 'Borgerholt' in medieval times.
Repository - Collection of the 'Institut Royal des Sciences Naturelles' (Brussels), catalogue number IRScN b3668.
Type locality - Outcrop 'Borgerhout Rivierenhof described by De Meuter et aI. (1976: 13), altitude -1.9 m O.D. (Ostend Datum), Borgerhout, Antwerp Province, Belgium.
Type stratum - Antwerpen Sands, Berchem Formation, Miocene.
Diagnosis - Spherical to ovoid proximochorate cyst ornamented with low, granulate prismatic luxuriae and numerous, long virgae. The distribution of the granules and simple, solid virgae is non-tabular. The virgae are acuminate, capitate or bifurcated. A low septum located at the antapex arises directly from the pedium and forms an irregular polygon. The geometry of this septum conforms to the outline of an antapical plate in a gonyaulacoid sexiform hypocystal pattern. The archeopyle is formed by the release of the third precingular plate. The operculum is free.
Description - Small cyst with a circular to ovoid ambitus. The homogeneous pedium is thin (less than 0.5 µm) and extends into luxuriae consisting of low granules, long virgae and an almost continuous, low antapical septum. The granules are solid with a diameter and a height of less than 1 µm. The solid virgae are circular in cross-section and their width remains even over almost the whole length of the shaft. Distally they taper rapidly towards sinuous acuminate, capitate or bifurcate tips. The virgae arise directly from the solid pedium, and some degree of proximal fusion with adjacent granules or virgae can occasionally be observed. The pedium forms an almost continuous antapical low ridge or septum (height less than 1.5 µm) with a subrectangular outline and rounded angles. The indentation in the six-sided polygon is directed towards the sulcal area. The septum is a reflection of the antapical plate 1'"'. The precingular archeopyle (type P) is large with smooth margins and rounded angles.
Dimensions - Holotype: length central body: 38 µm, equatorial width central body: 35 µm, length virgae: 6-7 µm. Range: length central body: 35 (37) 39 µm, equatorial width central body: 34 (36) 39 µm, length processes: 4 (6.5) 8 µm. Number of specimens measured: 9.
Remarks - Matsuoka et al. (1997), in their emendation of the genus Operculodinium, do not mention the presence of low septa or ridges, reflecting in part or completely a tabulation. Hence, the provisional assignment to the genus Operculodinium.
Comparison - This species is distinguished from all other Operculodinium species by the antapical ornamentation formed by a more or less continuous septum representing the six-sided gonyaulacoid antapical plate. The dimensions and ambitus of Operculodinium ? eirikianum HEAD et al., 1989 are similar. However, the luxuriae of the latter species consists of an irregular microreticulum of undulating muri and finely granulate virgae.
Occurrence - Lower - Middle Miocene (Antwerpen Sands and Zonderschot Sands of the Berchem Formation) of northern Belgium as Operculodinium sp. 1 (Louwye in press, Louwye et al. 2000).
Emended description (Soliman et al., 2009):
Operculodinium sp. 1. Louwye, 2000, tab. 1.
Operculodinium? borgerholtense Louwye, 2001, p. 126, 127, figs. 4.1–4.12; Jiménez-Moreno et al., 2006, pl. 2, figs. 1–5, pl. 9, fig. 7; Soliman, 2006, p. 54–56, pl. 39, figs. 5–22, text-fig. 22; Soliman and Piller, 2007a, p. 411, pl. 1, figs. 6–12.
Emended diagnosis. Small, thin-walled proximochorate cyst with spherical to subspherical central body bearing numerous solid erect processes and lower ornament. Processes nontabular, smooth or with granules, spinules, and short irregular branches. Lower ornament varies from low verrucae to round-topped coni, round-topped bacculae, and clavae. Low bounding septum and more densely ornamented surface demarcate six-sided antapical plate of subrectangular shape. Archeopyle precingular (3'') with well-defined angles, no accessory sutures. Operculum free.
Type locality. ‘Borgerhout Rivierenhof’ outcrop, Borgerhout, Antwerp Province, Belgium; for both holotype and paratype. A full description of the outcrop, lithology and position of the samples is given by De Meuter et al. (1976, p. 13, fig. 18).
Emended description. Central body thin walled (ca. 0.2–0.3 μm), spherical to subspherical in shape, bearing numerous solid processes and lower ornament. Processes and lower ornament nontabular and fairly evenly distributed over cyst, except in antapical area. Central body wall unstructured under LM but three appressed layers distinguishable under SEM: solid smooth thin inner and outer layers (ca. 0.03 μm) and much thicker densely granulate middle layer (Plate 3, fig.11 and inset). Structure continuous with lower ornament and presumably also with processes. Processes erect, narrow, initially of approximately even thickness and straight, tapering and often sinuous distally. Processes may be smooth for entire length but more commonly have granules, spinules, and short irregular branches, particularly along their distal half (as in holotype, but see Text-Figure 3 for full morphological range). Separation between adjacent process bases typically ca. 1.9–3.5 μm. Lower ornament ca. 0.3–0.7 μm in diameter and 0.6–1.0 μm high, conspicuous, varies from low verrucae to roundtopped coni, round-topped narrow bacculae, and occasionally clavae (Plate 3, fig. 7). Elements evenly distributed, typically separated from each other by one to two, or occasionally three times their diameter. Elements may be somewhat more sparsely distributed on specimens with smooth processes. Occasionally some, but never all, elements fused into low discontinuous ridges (Plate 3, figs. 4, 5, 9). At antapex, low (less than 1.5 μm) almost continuous (Plate 2, figs. 1–4) to discontinuous (Plate 3, figs. 2, 3) septum demarcates six-sided antapical plate. Contact with posterior sulcal plate (which overlaps antapical plate) is long and concave; contacts with posterior intercalary and sixth postcingular plates are short; resulting in subrectangular shape of antapical plate (Text-Figure 2). Ornament on antapical plate more densely clustered and irregular than elsewhere, with many adjacent elements fused at base (Plate 3, figs. 2, 3, 13, 14), and central body surface may be finely pitted (diameter, 0.05–0.20 μm) as seen in Plate 3, figs. 3, 14. Archeopyle formed by release of third precingular plate; margin entire, well-defined angles, no accessory sutures (Text-Figure 2). Archeopyle margin may be slightly raised and thickened, as observed under SEM (Plate 3, fig. 1). Operculum free. No other indications of tabulation.
Dimensions. Holotype: central body length, 38 μm, central body equatorial diameter, 35 μm, length of processes, 6–7 μm. Paratype: central body maximum diameter, 36 μm, length of processes, 5–6 μm. Range based on all specimens measured in the present study: central body maximum diameter, 23(32.8)41 μm, length of processes, 2.5(5.6)8.5 μm; 73 specimens measured (Text-Figure 4, Table 1). Average process width, 0.5(0.74)1.1 μm; 12 specimens measured under SEM.
Comparison. Operculodinium? eirikianum Head et al. 1989 emend. Head 1997, described from the Upper Miocene of the Labrador Sea, has a microreticulate central body surface. The marine acritarch Nannobarbophora walldalei Head 1996b, described from the Pliocene of eastern England, has root-like process bases and the vesicle surface has an irregularly scattered granulation unlike the more prominent and orderly distribution of lower ornament in O.? borgerholtense. Nannobarbophora gedlii Head 2003, described from the Lower Miocene of the Norwegian Sea, has hollow processes and a smooth to sparsely ornamented vesicle surface. Operculodinium? eirikianum has a range base in the uppermost Langhian (Louwye et al., 2007) and therefore overlaps stratigraphically with O.? borgerholtense. Nannobarbophora gedlii has a known range of upper Lower to Middle Miocene and also overlaps stratigraphically with O.? borgerholtense, whereas Nannobarbophora walldalei is not known from deposits older than Late Miocene (Head, 2003).