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Oligosphaeridium araneum
Oligosphaeridium araneum sp. nov., Niechwedowicz, M., 2022
Holotype: Niechwedowicz, M., 2022, Plate 6, figures 1–4
Type locality: Kłudzie South section, central Poland
Age: Middle upper Campanian–lowermost Maastrichtian
Original description: Niechwedowicz, M., 2022:
Diagnosis:
A species of Oligosphaeridium with relatively slim and long (equal to, or slightly longer than, central body diameter) processes. Terminations of the processes are short (branching occurs in their distalmost portion), and wide, significantly expanded laterally, forming perforate or fenestrate platforms.
Description:
The central body is subspheroidal, and consists of relatively thin (c. 0.5–1 µm) and homogeneous wall with rugulate outer surface; wall layering is not distinguishable,
except at the centre of the plates where the periphragm forms the mesotabular processes, endophragm and periphram appressed elsewhere.
Processes: are relatively robust, slim, and long (up to c. 4/3 of central body diameter), hollow with round cross-sections; the process stems are long (c. 85% of total process length), approximately constant in width or slightly tapering. The process terminations are short (branching occurs in distal c. 15% of the processes), but wide, distinctly expanded laterally (process termination width = c. 50% of total process length), forming perforate or fenestrate platforms that consist of networks of simple, branched, or interconnected spines, distally united by continuous trabecular ring bearing 5–9 short (c. 3–6 µm) free spines, perpendicular to process stems or slightly curved towards the central body (Figure 6; Plate 6, figures 3, 10, 11). The processes are generally comparable in size and shape, but apical, ps, and 1p processes are commonly slimmer.
Process formula: 40, 60’, 50’’, 1p, ps, 10’’’
Archaeopyle: apical (type A1–40 ) with angular margin
Operculum: usually free
Dimensions:
Holotype: Central body width: 36 µm, total process length: 44 µm, process base width: 6 µm, minimal process stem width: 2 µm, process termination length: 6 µm, process termination width: 23 µm, total process length/central body width ratio: 1.22, process termination length/total process length ratio: 0.14.
Range (minimum (mean) maximum):
Central body length (without operculum): 29 (33.6) 38 µm, central body width: 30 (36.5) 45 µm, total process length: 31 (40.6) 58 µm, process base width: 3 (5.5) 9 µm, minimal process stem width: 2 (2.1) 3 µm, process termination length: 3 (6.7) 12 µm, process termination width: 17 (21.5) 26 µm, total process length/central body width ratio: 0.82 (1.1) 1.3, process termination length/total process length ratio: 0.07 (0.16) 0.3 (31 specimens measured).
Remarks:
To date, surface tabulation of the central body in the genus Oligosphaeridium has only been recognised in O. abaculum Davey 1979. Its tabulation corresponds to the formula pr, 40, 60’, 6c, 60’’, 1p, 5 s, 10’’’ (Davey 1979, p. 430). As in O. abaculum, the process formula in O. araneum sp. nov. does not reflect the full tabulation: some processes are absent (pr, 10’’, all of the cingular and most sulcal processes; see Plate 6). The outer surface of the periphragm in O. araneum sp. nov. is finely rugulate (Plate 6, figure 16), but the rugulate nature of the ornament is only clearly visible under SEM (the wall surface may appear smooth to finely granular under TLM).
Oligosphaeridium pulcherrimum in Herngreen et al. (1998, pl. 4, fig. 2) has slim, relatively long processes, the distal extremities of which terminate with a regular trabecular margin bearing short spines. These features do not correspond to the original concept of O. pulcherrimum (see Deflandre and Cookson 1955, p. 270, 271, pl. 1, fig. 8, text-figs 21, 22); instead, the specimen probably belongs to O. araneum sp. nov. Comparison. Oligosphaeridium araneum sp. nov. is easily distinguished from other species of the genus by its slim and long process stems and characteristic process terminations. The most comparable species are O. pulcherrimum (Deflandre & Cookson 1955) Davey & Williams 1966, O. perforatum (Gocht 1959) Davey & Williams 1969, and O. perforatum? subsp. Colum Duxbury 1983. The processes in O. pulcherrimum are generally shorter than the central body diameter, with wider and shorter stems and a pronounced branching of processes starting at c. 1/2–2/3 of the total process length. Furthermore, while process extremities in both species are fenestrate, in O. pulcherrimum they terminate with an irregular margin, rather than with ring-shaped trabeculae as in the new species.
Oligosphaeridium perforatum (see Plate 7, figures 9, 10) has relatively short processes, with their distal tips in the form of irregularly perforated platforms with a ragged margin devoid of spines. The processes in O. perforatum? colum have relatively short stems, and their distal extremities are significantly more expanded and highly fenestrated.
Holotype: Niechwedowicz, M., 2022, Plate 6, figures 1–4
Type locality: Kłudzie South section, central Poland
Age: Middle upper Campanian–lowermost Maastrichtian
Original description: Niechwedowicz, M., 2022:
Diagnosis:
A species of Oligosphaeridium with relatively slim and long (equal to, or slightly longer than, central body diameter) processes. Terminations of the processes are short (branching occurs in their distalmost portion), and wide, significantly expanded laterally, forming perforate or fenestrate platforms.
Description:
The central body is subspheroidal, and consists of relatively thin (c. 0.5–1 µm) and homogeneous wall with rugulate outer surface; wall layering is not distinguishable,
except at the centre of the plates where the periphragm forms the mesotabular processes, endophragm and periphram appressed elsewhere.
Processes: are relatively robust, slim, and long (up to c. 4/3 of central body diameter), hollow with round cross-sections; the process stems are long (c. 85% of total process length), approximately constant in width or slightly tapering. The process terminations are short (branching occurs in distal c. 15% of the processes), but wide, distinctly expanded laterally (process termination width = c. 50% of total process length), forming perforate or fenestrate platforms that consist of networks of simple, branched, or interconnected spines, distally united by continuous trabecular ring bearing 5–9 short (c. 3–6 µm) free spines, perpendicular to process stems or slightly curved towards the central body (Figure 6; Plate 6, figures 3, 10, 11). The processes are generally comparable in size and shape, but apical, ps, and 1p processes are commonly slimmer.
Process formula: 40, 60’, 50’’, 1p, ps, 10’’’
Archaeopyle: apical (type A1–40 ) with angular margin
Operculum: usually free
Dimensions:
Holotype: Central body width: 36 µm, total process length: 44 µm, process base width: 6 µm, minimal process stem width: 2 µm, process termination length: 6 µm, process termination width: 23 µm, total process length/central body width ratio: 1.22, process termination length/total process length ratio: 0.14.
Range (minimum (mean) maximum):
Central body length (without operculum): 29 (33.6) 38 µm, central body width: 30 (36.5) 45 µm, total process length: 31 (40.6) 58 µm, process base width: 3 (5.5) 9 µm, minimal process stem width: 2 (2.1) 3 µm, process termination length: 3 (6.7) 12 µm, process termination width: 17 (21.5) 26 µm, total process length/central body width ratio: 0.82 (1.1) 1.3, process termination length/total process length ratio: 0.07 (0.16) 0.3 (31 specimens measured).
Remarks:
To date, surface tabulation of the central body in the genus Oligosphaeridium has only been recognised in O. abaculum Davey 1979. Its tabulation corresponds to the formula pr, 40, 60’, 6c, 60’’, 1p, 5 s, 10’’’ (Davey 1979, p. 430). As in O. abaculum, the process formula in O. araneum sp. nov. does not reflect the full tabulation: some processes are absent (pr, 10’’, all of the cingular and most sulcal processes; see Plate 6). The outer surface of the periphragm in O. araneum sp. nov. is finely rugulate (Plate 6, figure 16), but the rugulate nature of the ornament is only clearly visible under SEM (the wall surface may appear smooth to finely granular under TLM).
Oligosphaeridium pulcherrimum in Herngreen et al. (1998, pl. 4, fig. 2) has slim, relatively long processes, the distal extremities of which terminate with a regular trabecular margin bearing short spines. These features do not correspond to the original concept of O. pulcherrimum (see Deflandre and Cookson 1955, p. 270, 271, pl. 1, fig. 8, text-figs 21, 22); instead, the specimen probably belongs to O. araneum sp. nov. Comparison. Oligosphaeridium araneum sp. nov. is easily distinguished from other species of the genus by its slim and long process stems and characteristic process terminations. The most comparable species are O. pulcherrimum (Deflandre & Cookson 1955) Davey & Williams 1966, O. perforatum (Gocht 1959) Davey & Williams 1969, and O. perforatum? subsp. Colum Duxbury 1983. The processes in O. pulcherrimum are generally shorter than the central body diameter, with wider and shorter stems and a pronounced branching of processes starting at c. 1/2–2/3 of the total process length. Furthermore, while process extremities in both species are fenestrate, in O. pulcherrimum they terminate with an irregular margin, rather than with ring-shaped trabeculae as in the new species.
Oligosphaeridium perforatum (see Plate 7, figures 9, 10) has relatively short processes, with their distal tips in the form of irregularly perforated platforms with a ragged margin devoid of spines. The processes in O. perforatum? colum have relatively short stems, and their distal extremities are significantly more expanded and highly fenestrated.