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Amphorosphaeridium fenestratum
From Fensome et al., 2019:
Amphorosphaeridium fenestratum, Davey, 1969c, p.30–33, pl.1, fig.6; pl.2, figs.2,4–6; pl.3, figs.1–3; text-fig.1, nos.2a–e; text-fig.2.
Holotype: Davey, 1969c, pl.3, figs.1–2; Fensome et al., 1993a, fig.1 — p.1181; figs.1–2 — p.1183.
Age: Campanian–Maastrichtian.
Locus typicus: Northern Natal, South Africa
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Original description: [Davey, 1969, p. 30-31]:
Diagnosis:
Central body subspherical, wall moderately thick, fibrous and pitted.
Processes one or two, rarely three, per plate-area, of variable width but constant length (approximately one-third central body diameter); they are typically hollow, tubiform and spinous distally. Apical process broad, branching; antapical process tubiform, distinctively large.
Archaeopyle usually present.
Description:
The wall of the central body is 1 to 1.5 µm thick and is fibrous with subpolygonal to elongate pits or perforations between the fibres.
The cingulum, which is rarely present, may be delimited by parallel rows of aligned pits.
The processes are also fibrous, the fibres of each process splaying out proximally over the surface of the central body. The majority of the processes are tubiform and are angular in cross-section, usually quadrilateral, due to three or four longitudinal ribs ([Davey, 1969] fig. 1, no. 2a, b, d). Solid processes sometimes also occur but are always in a minority and are usually restricted to the sulcal region. The processes vary considerably in width on an individual and on different specimens depending mainly on the number of processes per plate-area present. The processes on specimens possessing one process per plate-area are typically broader than those with two or three per plate-area. Normally, however, there are one or two processes per plate-area and any additional ones are finer, perhaps solid, although being of equal length to the normal processes. The processes have broad bases and taper distally before expanding to produce a small number of spines. The latter of the tubiform processes are usually formed by extensions of the more strongly developed fibres (longitudinal ribs) of the processes and are often recurved to some extent. The broader processes are very rarely fenestrate. The sulcal region, as mentioned earlier, may either bear relatively fine solid processes or may be devoid of any processes. In the latter case this region is surrounded by normal processes which tend to be joined proximally and so clearly delimit it ([Davey, 1969c] Pl. 1, fig. 6). Some process alignment may be noticeable along the cingulum. The apical process is a broad fibrous structure which gives rise medially to two to four subsidiary processes; the antapical process is similar to the normal processes in structure but is larger.
The archaeopyle is of a rounded triangular shape and is formed by the loss of the reflected precingular plate 3" - Type P of Evitt (1967).
Dimensions:
Holotype: central body diameter 57x64 µm, process length 25-27 µm.
Range of 12 specimens: central body diameter 52(60)77 µm, process length 19(21)27 µm.
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Emended description Niechwedowicz, 2021:
Emended diagnosis. Gonyaulacacean (leptodinioid) chorate cysts of intermediate size, with ovoidal central body, and numerous, relatively long and robust processes. Central body and process walls are more or less fibrous. The processes are generally hollow, intratabular, one to five per plate area; neighbouring processes may be joined. Apical and antapical prominences are occasionally present, expressed by enlarged processes. The tabulation is indicated by the archaeopyle and arrangement of the processes. The archaeopyle is precingular, type 1 P (30’), operculum is free or attached.
Emended description. Chorate cysts of intermediate size, with ovoidal central body and numerous (c. 60) robust processes. Central body wall and process walls are more or less fibrous (or fibro-pitted). The processes are constant in length (c. 1/3–1/2 of central body diameter), but vary in width; generally tapering and hollow throughout entire length, rarely acuminate and distally solid (most commonly sulcal processes). The processes are relatively wide proximally, typically with circular bases, and tapering, distally only slightly expanded, terminating with aculeate tip. The processes are intratabular, commonly arranged in latitudinal and meridional rows. The processes arising from the larger pre- and postcingular plates are commonly penitabular. Process distribution is more or less uniform; the number of processes per plate (1–5) depends on the plate size and position on cyst: one process per 1p plate and each sulcal plate, 1–3 processes per smaller plate of other types (60’, 10’’, cingular, and apical plates), 3–5 processes per larger plate (rest of pre- and postcingulars, and antapical plate). Neighbouring processes occupying particular plates sometimes are connected proximally, or are completely fused. Apical and antapical prominences are occasionally evident, expressed by enlarged (widened) process. The tabulation formula is 40, 60’, 6c, 60’’, 1p, 5 s (ps, ls, rs, ras, as), 10’’’, more or less clearly expressed by the distribution of the processes, indicating leptodinioid pattern (sexiform antapex, L-type ventral plate arrangement, and neutral torsion of the hypocyst). The archaeopyle is precingular, type 1 P (30’), operculum is free or attached.
Dimensions (minimum (mean) maximum).
Central body length: 49 (57.8) 65 mm, central body width: 43 (51.7) 59 mm, process length: 16 (20.9) 23 mm, total cyst length: 82 (95.4) 106 mm, total cyst width: 76 (87) 96 mm, process length/central body width ratio: 0.34 (0.42) 0.48 (11 specimens measured).
Remarks. The ovoidal shape of the central body, the presence of the 1 P archaeopyle and the distribution of processes (arranged in latitudinal and meridional rows, sulcal processes typically slimmer than others and distally solid, except for those occupying plates as and ps) make the cyst orientation easy to determine. The processes in A. fenestratum are of constant length, but occasionally exhibit significant variability in width on a single specimen. Essentially, the processes have circular bases, and their number per particular plate is constant. However, some of the neighbouring processes occupying the same plate area may connect proximally or may be almost completely fused; such processes have wider bases (oval, elliptical, or subangular in cross-section), and have two or more tips (Plate 1, figures 9–11). The subspecies differentiation of Davey (1969) is confusing, since in both subspecies the processes may be branched/connected (see Davey 1969, p. 31–33). The degree of process fusion in A. fenestratum is considered intraspecifically variable and, consequently, the two subspecies are synonymised herein. Peyrot (2011, p. 284, 289) included the specimens of A. fenestratum that lack enlarged antapical process (including the holotype – see Davey 1969, pl. 3, figs 1, 2) into Exochosphaeridium majus, significantly broadening its concept. The concept of Amphorosphaeridium refers to the presence of prominences at both poles (Davey 1969, p. 30), but this is not the most distinctive feature of A. fenestratum, in which the prominences may be absent or difficult to recognise. Based on the material studied herein, a single enlarged process at the apex may be one of the apical processes (e.g. the process occupying plate 20, as in the specimen in Figure 3; Plate 1, figures 4–7), which does not occupy the central polar position. The antapical pole of the same specimen is characterised by the presence of four processes, none of which are enlarged (significantly wider) or occupy the central polar position. The distinction of the antapical prominence in this case may be marked by a partial fusion of processes (Plate 1, figures 6, 7). It appears that the processes occupying plate 10’’’ may be completely fused, forming one relatively wide process. This would explain the presence or absence of an antapical prominence in the type material (see Davey 1969, pl. 1, fig. 6, pl. 2, fig. 4, pl. 3, figs 1–3). In contrast, Exochosphaeridium may bear only one prominence (an enlarged apical process, commonly branched or expanded distally; see Plate 1, figure 16); but, as in Amphorosphaeridium, it is not always present. Thus, the most characteristic feature of A. fenestratum is the development of processes and their arrangement, in which it clearly differs from E. majus (Plate 1, figures 13–16). Consequently, the synonymy proposed by Peyrot (2011) is rejected.
Comparison. Exochosphaeridium majus (Lejeune-Carpentier 1940) Peyrot 2011 (see Plate 1, figures 13–16) most resembles Amphorosphaeridium fenestratum, both in overall appearance and in its fibrous (or fibro-pitted) wall. What differentiates the two species is the process development. In A. fenestratum, processes are usually relatively wide and distinctly hollow throughout their entire length; by contrast, E. majus bears solid and hollow processes, but the latter are commonly acuminate, being hollow only proximally (if at all). Furthermore, the processes in E. majus are not arranged in a manner indicating tabulation. Amphorosphaeridium fenestratum may bear apical and antapical prominences, while E. majus may bear only the apical one. Pervosphaeridium elegans Louwye 1997 and P. tubuloaculeatum Slimani 1994 also resemble A. fenestratum in possessing hollow processes. Pervosphaeridium elegans (Plate 1, figures 17, 18) differs in having more slender and relatively longer (c. 3/4 of central body diameter) processes, constant in width on individual specimens (except for the sulcal processes) and never connected proximally. Pervosphaeridium tubuloaculeatum (Plate 1, figures 19–21) is significantly smaller, and it can be distinguished by the morphology of its processes (degree of tapering of the processes and their termination type). Furthermore, Pervosphaeridium has an archaeopyle of type 2 P.
Recorded stratigraphical range. Middle upper Campanian–lowermost Maastrichtian, ‘Inoceramus’ altus Zone–lower Endocostea typica Zone (recorded in Piotrawin, Podole, Kłudzie North, Kłudzie South, and Dziurk ow).
Amphorosphaeridium fenestratum, Davey, 1969c, p.30–33, pl.1, fig.6; pl.2, figs.2,4–6; pl.3, figs.1–3; text-fig.1, nos.2a–e; text-fig.2.
Holotype: Davey, 1969c, pl.3, figs.1–2; Fensome et al., 1993a, fig.1 — p.1181; figs.1–2 — p.1183.
Age: Campanian–Maastrichtian.
Locus typicus: Northern Natal, South Africa
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Original description: [Davey, 1969, p. 30-31]:
Diagnosis:
Central body subspherical, wall moderately thick, fibrous and pitted.
Processes one or two, rarely three, per plate-area, of variable width but constant length (approximately one-third central body diameter); they are typically hollow, tubiform and spinous distally. Apical process broad, branching; antapical process tubiform, distinctively large.
Archaeopyle usually present.
Description:
The wall of the central body is 1 to 1.5 µm thick and is fibrous with subpolygonal to elongate pits or perforations between the fibres.
The cingulum, which is rarely present, may be delimited by parallel rows of aligned pits.
The processes are also fibrous, the fibres of each process splaying out proximally over the surface of the central body. The majority of the processes are tubiform and are angular in cross-section, usually quadrilateral, due to three or four longitudinal ribs ([Davey, 1969] fig. 1, no. 2a, b, d). Solid processes sometimes also occur but are always in a minority and are usually restricted to the sulcal region. The processes vary considerably in width on an individual and on different specimens depending mainly on the number of processes per plate-area present. The processes on specimens possessing one process per plate-area are typically broader than those with two or three per plate-area. Normally, however, there are one or two processes per plate-area and any additional ones are finer, perhaps solid, although being of equal length to the normal processes. The processes have broad bases and taper distally before expanding to produce a small number of spines. The latter of the tubiform processes are usually formed by extensions of the more strongly developed fibres (longitudinal ribs) of the processes and are often recurved to some extent. The broader processes are very rarely fenestrate. The sulcal region, as mentioned earlier, may either bear relatively fine solid processes or may be devoid of any processes. In the latter case this region is surrounded by normal processes which tend to be joined proximally and so clearly delimit it ([Davey, 1969c] Pl. 1, fig. 6). Some process alignment may be noticeable along the cingulum. The apical process is a broad fibrous structure which gives rise medially to two to four subsidiary processes; the antapical process is similar to the normal processes in structure but is larger.
The archaeopyle is of a rounded triangular shape and is formed by the loss of the reflected precingular plate 3" - Type P of Evitt (1967).
Dimensions:
Holotype: central body diameter 57x64 µm, process length 25-27 µm.
Range of 12 specimens: central body diameter 52(60)77 µm, process length 19(21)27 µm.
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Emended description Niechwedowicz, 2021:
Emended diagnosis. Gonyaulacacean (leptodinioid) chorate cysts of intermediate size, with ovoidal central body, and numerous, relatively long and robust processes. Central body and process walls are more or less fibrous. The processes are generally hollow, intratabular, one to five per plate area; neighbouring processes may be joined. Apical and antapical prominences are occasionally present, expressed by enlarged processes. The tabulation is indicated by the archaeopyle and arrangement of the processes. The archaeopyle is precingular, type 1 P (30’), operculum is free or attached.
Emended description. Chorate cysts of intermediate size, with ovoidal central body and numerous (c. 60) robust processes. Central body wall and process walls are more or less fibrous (or fibro-pitted). The processes are constant in length (c. 1/3–1/2 of central body diameter), but vary in width; generally tapering and hollow throughout entire length, rarely acuminate and distally solid (most commonly sulcal processes). The processes are relatively wide proximally, typically with circular bases, and tapering, distally only slightly expanded, terminating with aculeate tip. The processes are intratabular, commonly arranged in latitudinal and meridional rows. The processes arising from the larger pre- and postcingular plates are commonly penitabular. Process distribution is more or less uniform; the number of processes per plate (1–5) depends on the plate size and position on cyst: one process per 1p plate and each sulcal plate, 1–3 processes per smaller plate of other types (60’, 10’’, cingular, and apical plates), 3–5 processes per larger plate (rest of pre- and postcingulars, and antapical plate). Neighbouring processes occupying particular plates sometimes are connected proximally, or are completely fused. Apical and antapical prominences are occasionally evident, expressed by enlarged (widened) process. The tabulation formula is 40, 60’, 6c, 60’’, 1p, 5 s (ps, ls, rs, ras, as), 10’’’, more or less clearly expressed by the distribution of the processes, indicating leptodinioid pattern (sexiform antapex, L-type ventral plate arrangement, and neutral torsion of the hypocyst). The archaeopyle is precingular, type 1 P (30’), operculum is free or attached.
Dimensions (minimum (mean) maximum).
Central body length: 49 (57.8) 65 mm, central body width: 43 (51.7) 59 mm, process length: 16 (20.9) 23 mm, total cyst length: 82 (95.4) 106 mm, total cyst width: 76 (87) 96 mm, process length/central body width ratio: 0.34 (0.42) 0.48 (11 specimens measured).
Remarks. The ovoidal shape of the central body, the presence of the 1 P archaeopyle and the distribution of processes (arranged in latitudinal and meridional rows, sulcal processes typically slimmer than others and distally solid, except for those occupying plates as and ps) make the cyst orientation easy to determine. The processes in A. fenestratum are of constant length, but occasionally exhibit significant variability in width on a single specimen. Essentially, the processes have circular bases, and their number per particular plate is constant. However, some of the neighbouring processes occupying the same plate area may connect proximally or may be almost completely fused; such processes have wider bases (oval, elliptical, or subangular in cross-section), and have two or more tips (Plate 1, figures 9–11). The subspecies differentiation of Davey (1969) is confusing, since in both subspecies the processes may be branched/connected (see Davey 1969, p. 31–33). The degree of process fusion in A. fenestratum is considered intraspecifically variable and, consequently, the two subspecies are synonymised herein. Peyrot (2011, p. 284, 289) included the specimens of A. fenestratum that lack enlarged antapical process (including the holotype – see Davey 1969, pl. 3, figs 1, 2) into Exochosphaeridium majus, significantly broadening its concept. The concept of Amphorosphaeridium refers to the presence of prominences at both poles (Davey 1969, p. 30), but this is not the most distinctive feature of A. fenestratum, in which the prominences may be absent or difficult to recognise. Based on the material studied herein, a single enlarged process at the apex may be one of the apical processes (e.g. the process occupying plate 20, as in the specimen in Figure 3; Plate 1, figures 4–7), which does not occupy the central polar position. The antapical pole of the same specimen is characterised by the presence of four processes, none of which are enlarged (significantly wider) or occupy the central polar position. The distinction of the antapical prominence in this case may be marked by a partial fusion of processes (Plate 1, figures 6, 7). It appears that the processes occupying plate 10’’’ may be completely fused, forming one relatively wide process. This would explain the presence or absence of an antapical prominence in the type material (see Davey 1969, pl. 1, fig. 6, pl. 2, fig. 4, pl. 3, figs 1–3). In contrast, Exochosphaeridium may bear only one prominence (an enlarged apical process, commonly branched or expanded distally; see Plate 1, figure 16); but, as in Amphorosphaeridium, it is not always present. Thus, the most characteristic feature of A. fenestratum is the development of processes and their arrangement, in which it clearly differs from E. majus (Plate 1, figures 13–16). Consequently, the synonymy proposed by Peyrot (2011) is rejected.
Comparison. Exochosphaeridium majus (Lejeune-Carpentier 1940) Peyrot 2011 (see Plate 1, figures 13–16) most resembles Amphorosphaeridium fenestratum, both in overall appearance and in its fibrous (or fibro-pitted) wall. What differentiates the two species is the process development. In A. fenestratum, processes are usually relatively wide and distinctly hollow throughout their entire length; by contrast, E. majus bears solid and hollow processes, but the latter are commonly acuminate, being hollow only proximally (if at all). Furthermore, the processes in E. majus are not arranged in a manner indicating tabulation. Amphorosphaeridium fenestratum may bear apical and antapical prominences, while E. majus may bear only the apical one. Pervosphaeridium elegans Louwye 1997 and P. tubuloaculeatum Slimani 1994 also resemble A. fenestratum in possessing hollow processes. Pervosphaeridium elegans (Plate 1, figures 17, 18) differs in having more slender and relatively longer (c. 3/4 of central body diameter) processes, constant in width on individual specimens (except for the sulcal processes) and never connected proximally. Pervosphaeridium tubuloaculeatum (Plate 1, figures 19–21) is significantly smaller, and it can be distinguished by the morphology of its processes (degree of tapering of the processes and their termination type). Furthermore, Pervosphaeridium has an archaeopyle of type 2 P.
Recorded stratigraphical range. Middle upper Campanian–lowermost Maastrichtian, ‘Inoceramus’ altus Zone–lower Endocostea typica Zone (recorded in Piotrawin, Podole, Kłudzie North, Kłudzie South, and Dziurk ow).