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Barssidinium pliocenicum
Barssidinium pliocenicum, (Head, 1993, p.40-41, fig.22, nos.5-14; fig.23), Head, 1994a, p.296; Emendation: De Schepper et al., 2004, p.634,636, as Barssidinium pliocenicum.
Originally Sumatradinium, subsequently (and now) Barssidinium.
Taxonomic junior synonym: Barssidinium wrennii, according to De Schepper et al. (2004, p.634).
Holotype: Head, 1993, fig.22, no.11; De Schepper et al., 2004, fig.10.7–9.
Age: latest Pliocene.
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Original description: [Head, 1993]:
Diagnosis:
Skolochorate cysts; central body with weak to moderate dorsoventral compression and rounded pentagonal ambitus. Wall composed of two closely appressed layers and has a smooth to shagreenate surface. Periphragm thinner than endophragm and sometimes revealed by wrinkles on wall surface.
Processes relatively short for genus, hollow with annular thickenings developed on inner surface of process stems, and distally aculeate. Archeopyle a rounded 2a hexa intercalary, operculum free, occasionally adherent.
Description:
Central body typically light to medium brown although occasional pale, thin specimens were seen. Surface of central body smooth to shagreenate and appears finely blotched in plan view (e.g., Figure 22.13, 22.14) presumably reflecting slight irregularities in wall thickness.
Processes hollow and distally aculeate (aculeae around 1.0 µm, and usually less than 2.0 µm, in length; may be recurved or flared). Processes often narrow distally and on some specimens are constricted also at base. Annular thickenings (around 2-6, number generally increasing with process length) developed on inner surface of process stems. Processes generally unbranched but specimens occasionally seen also with one or two? bifurcating processes (Figures 22.10, 23). Observations on occasional specimens whose walls were incompletely permeated by Cellosizef mounting medium suggest about 6-8 internal vacuities or tubules arranged in ring within wall at base of each process (see Figure 22.5). Process distribution apparently non-tabular, usually covering entire cyst but often concentrated around ambitus.
Dimensions:
Holotype: central body length, 73 µm; central body width, 74 µm; archeopyle width, 34 µm; archeopyle height, 26 µm; archeopyle ratio (h/w), 0.76; average process length, 9 µm; ratio of average process length/averaged diameter of central body, 0.12.
Range: central body length, 54(68.1)80 µm; central body width, 57(70.2)82 µm: based on 12 specimens measured.
Archeopyle width, 32(34.8)39 µm; archeopyle height, 26(28.1)30 µm; archeopyle ratio (h/w), 0.73(0.809)0.86, based on seven specimens measured. Average process length, 4.5(9.7)15 µm: based on 57 specimens measured. Ratio of average process length/ averaged diameter of central body, 0.089(0.1438)0.202: based on 43 specimens measured (see Figure 24).
Affinities/Comparison:
Sumatradinium hispidum, from the middle Miocene to Pliocene of Sumatra (Drugg, 1970) is somewhat larger (length, 78-97 Am) than the St. Erth specimens, has proportionally shorter processes which are usually aculeate, and has a granulate surface. Sumatradinium soucouyantae from the lower through lower upper Miocene of Maryland, U.S.A. (de Verteuil and Norris, 1992) differs in having a reticulate central body surface and evexate processes. "Sumatradinium sp. 'furcate spines'" of Lund and LundChristensen (in Daniels et al., 1990, p. 37, P1. 10, fig. 8), from the middle or upper Miocene of Germany, resembles the St. Erth specimens but is larger, having a central body diameter of about 90 Am (measured from illustration). A specimen from the lower Pliocene, nannofossil zone NN 12, of ODP Site 646 in the Labrador Sea (as Polysphaeridium? sp. 1 in Head et al., 1989a, p. 439, P1. 7, fig. 3) differs from the St. Erth specimens in having processes that are much longer (about 21 Arm). Previous records. Sumatradinium sp. of Williams (1978, P1. 7, fig. 11), from the lower upper Pliocene of offshore northwest Africa (occurring within the Discoaster tamalis (CN12a) subzone of Bukry, 1973, correlated via Bukry, 1978), and Sumatradinium sp. of Bujak and Davies (1983, PI. 10, fig. 10), from the Pliocene of offshore eastern Canada, are both probably conspecific with the St. Erth specimens although the size of Bujak and Davies' (1983) specimen cannot be determined from the illustration. "Xandarodinium variabile" of de Vernal and Mudie (1989a, P1. 5, fig. 7), from the upper Pliocene, nannofossil zone NN16 or 17, of ODP Site 646 in the Labrador Sea, and Sumatradinium sp., from the mid-Pliocene Coralline Crag, eastern England (Head, 1990c; unpublished data), seem to fall within the range of morphologic variation seen in the St. Erth specimens. However, processes on the St. Erth specimens typically are rather shorter and stouter than those occurring on specimens from either the Coralline Crag (unpublished data) or the illustrated specimen from the Labrador Sea (de Vernal and Mudie, 1989a). Stratigraphic range.Sumatradinium pliocenicum n. sp. is known from the Pliocene (this study and in Williams, 1978, and Bujak and Davies, 1983; and possibly in de Vernal and Mudie, 1989a, and Head, 1990c) together with a questionable occurrence in the middle or upper Miocene (Lund and Lund-Christensen in Daniels et al., 1990).
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Emended description:
De Schepper et al., 2004:
Diagnosis:
A species of Barssidinium with rounded pentagonal ambitus. Central body moderately dorsoventrally compressed, composed of two closely appressed layers, outer layer thinner than inner layer. Surface smooth to shagreenate, sometimes marked by low ridges.
Processes hollow and distally aculeate, with annular thickenings on inner surface of process stems. Processes not longer than ca. 15 µm. Process distribution concentrated around ambital area, absent or strongly reduced in midventral and mid-dorsal area, reflecting tabulation variably over cyst. Faint and fine sutural lineations may occur around archeopyle and cingulum on dorsal surface and may extend to ventral surface. Archeopyle 2a hexa or penta intercalary, rounded angles, occasional accessory sutures. Operculum free or adherent.
Description:
Central body light to medium brown, although pale when exposed to oxidation. Wall composed of two closely appressed layers, outer layer thinner than inner layer and may form wrinkles over surface (as in holotype) or show no visible separation (as in the Belgian specimens).
Surface smooth to shagreenate, sometimes marked by very low ridges and other irregularities in wall thickness, giving faintly blotched appearance in plain view (e.g., Head, 1993, fig. 22.13, 22.14; Fig. 10.2).
Processes, formed from outer wall layer, are hollow and distally aculeate (aculeae about 1.0 µm, and usually less than 2.0 µm, in length; may be recurved or flared, e.g., see SEM in Head, 1997, fig. 17.14). Processes often narrow distally, just below process termination, and on some specimens are constricted also at base and elsewhere along process length. Processes usually closed distally. Annular thickenings (around two to six, number generally increasing with process length) developed on inner surface of process stems. Processes generally unbranched, but bifurcate processes occasionally developed on one or both lateral margins (Head, 1993, figs. 22.10, 23; Fig. 10.1; but not seen on holotype). Processes usually cover entire cyst but concentrated around ambitus. On Belgian specimens, processes show some alignment on or near plate boundaries, particularly along cingular margins and around third postcingular plate, but also occur randomly.
Tabulation also expressed on Belgian specimens by pale, narrow, sutural lines (presumably thinning of wall) developed variably over surface, evident particularly along cingulum and in area around archeopyle.
Archeopyle 2a intercalary, rounded outline, variably five-sided camerate, or six-sided linteloid; accessory sutures present. Hexa archeopyle contacts one apical (39), two intercalary (1a and 3a), and three precingular (30, 40, and 50) plates (Figs. 8.6–8.10, 9.5–9.9). Penta archeopyle contacts plates 39, 1a, 3a, 30, and 40 (Figs. 8.1–8.5, 8.11, 8.12, 9.1–9.4).
Hence, the penta geometry involves plate 40 contacting 3a (Figs. 8.1–8.5, 8.11, 8.12, 9.1–9.4). A penta geometry where plate 40 contacts plate 1a has not been observed.
Originally Sumatradinium, subsequently (and now) Barssidinium.
Taxonomic junior synonym: Barssidinium wrennii, according to De Schepper et al. (2004, p.634).
Holotype: Head, 1993, fig.22, no.11; De Schepper et al., 2004, fig.10.7–9.
Age: latest Pliocene.
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Original description: [Head, 1993]:
Diagnosis:
Skolochorate cysts; central body with weak to moderate dorsoventral compression and rounded pentagonal ambitus. Wall composed of two closely appressed layers and has a smooth to shagreenate surface. Periphragm thinner than endophragm and sometimes revealed by wrinkles on wall surface.
Processes relatively short for genus, hollow with annular thickenings developed on inner surface of process stems, and distally aculeate. Archeopyle a rounded 2a hexa intercalary, operculum free, occasionally adherent.
Description:
Central body typically light to medium brown although occasional pale, thin specimens were seen. Surface of central body smooth to shagreenate and appears finely blotched in plan view (e.g., Figure 22.13, 22.14) presumably reflecting slight irregularities in wall thickness.
Processes hollow and distally aculeate (aculeae around 1.0 µm, and usually less than 2.0 µm, in length; may be recurved or flared). Processes often narrow distally and on some specimens are constricted also at base. Annular thickenings (around 2-6, number generally increasing with process length) developed on inner surface of process stems. Processes generally unbranched but specimens occasionally seen also with one or two? bifurcating processes (Figures 22.10, 23). Observations on occasional specimens whose walls were incompletely permeated by Cellosizef mounting medium suggest about 6-8 internal vacuities or tubules arranged in ring within wall at base of each process (see Figure 22.5). Process distribution apparently non-tabular, usually covering entire cyst but often concentrated around ambitus.
Dimensions:
Holotype: central body length, 73 µm; central body width, 74 µm; archeopyle width, 34 µm; archeopyle height, 26 µm; archeopyle ratio (h/w), 0.76; average process length, 9 µm; ratio of average process length/averaged diameter of central body, 0.12.
Range: central body length, 54(68.1)80 µm; central body width, 57(70.2)82 µm: based on 12 specimens measured.
Archeopyle width, 32(34.8)39 µm; archeopyle height, 26(28.1)30 µm; archeopyle ratio (h/w), 0.73(0.809)0.86, based on seven specimens measured. Average process length, 4.5(9.7)15 µm: based on 57 specimens measured. Ratio of average process length/ averaged diameter of central body, 0.089(0.1438)0.202: based on 43 specimens measured (see Figure 24).
Affinities/Comparison:
Sumatradinium hispidum, from the middle Miocene to Pliocene of Sumatra (Drugg, 1970) is somewhat larger (length, 78-97 Am) than the St. Erth specimens, has proportionally shorter processes which are usually aculeate, and has a granulate surface. Sumatradinium soucouyantae from the lower through lower upper Miocene of Maryland, U.S.A. (de Verteuil and Norris, 1992) differs in having a reticulate central body surface and evexate processes. "Sumatradinium sp. 'furcate spines'" of Lund and LundChristensen (in Daniels et al., 1990, p. 37, P1. 10, fig. 8), from the middle or upper Miocene of Germany, resembles the St. Erth specimens but is larger, having a central body diameter of about 90 Am (measured from illustration). A specimen from the lower Pliocene, nannofossil zone NN 12, of ODP Site 646 in the Labrador Sea (as Polysphaeridium? sp. 1 in Head et al., 1989a, p. 439, P1. 7, fig. 3) differs from the St. Erth specimens in having processes that are much longer (about 21 Arm). Previous records. Sumatradinium sp. of Williams (1978, P1. 7, fig. 11), from the lower upper Pliocene of offshore northwest Africa (occurring within the Discoaster tamalis (CN12a) subzone of Bukry, 1973, correlated via Bukry, 1978), and Sumatradinium sp. of Bujak and Davies (1983, PI. 10, fig. 10), from the Pliocene of offshore eastern Canada, are both probably conspecific with the St. Erth specimens although the size of Bujak and Davies' (1983) specimen cannot be determined from the illustration. "Xandarodinium variabile" of de Vernal and Mudie (1989a, P1. 5, fig. 7), from the upper Pliocene, nannofossil zone NN16 or 17, of ODP Site 646 in the Labrador Sea, and Sumatradinium sp., from the mid-Pliocene Coralline Crag, eastern England (Head, 1990c; unpublished data), seem to fall within the range of morphologic variation seen in the St. Erth specimens. However, processes on the St. Erth specimens typically are rather shorter and stouter than those occurring on specimens from either the Coralline Crag (unpublished data) or the illustrated specimen from the Labrador Sea (de Vernal and Mudie, 1989a). Stratigraphic range.Sumatradinium pliocenicum n. sp. is known from the Pliocene (this study and in Williams, 1978, and Bujak and Davies, 1983; and possibly in de Vernal and Mudie, 1989a, and Head, 1990c) together with a questionable occurrence in the middle or upper Miocene (Lund and Lund-Christensen in Daniels et al., 1990).
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Emended description:
De Schepper et al., 2004:
Diagnosis:
A species of Barssidinium with rounded pentagonal ambitus. Central body moderately dorsoventrally compressed, composed of two closely appressed layers, outer layer thinner than inner layer. Surface smooth to shagreenate, sometimes marked by low ridges.
Processes hollow and distally aculeate, with annular thickenings on inner surface of process stems. Processes not longer than ca. 15 µm. Process distribution concentrated around ambital area, absent or strongly reduced in midventral and mid-dorsal area, reflecting tabulation variably over cyst. Faint and fine sutural lineations may occur around archeopyle and cingulum on dorsal surface and may extend to ventral surface. Archeopyle 2a hexa or penta intercalary, rounded angles, occasional accessory sutures. Operculum free or adherent.
Description:
Central body light to medium brown, although pale when exposed to oxidation. Wall composed of two closely appressed layers, outer layer thinner than inner layer and may form wrinkles over surface (as in holotype) or show no visible separation (as in the Belgian specimens).
Surface smooth to shagreenate, sometimes marked by very low ridges and other irregularities in wall thickness, giving faintly blotched appearance in plain view (e.g., Head, 1993, fig. 22.13, 22.14; Fig. 10.2).
Processes, formed from outer wall layer, are hollow and distally aculeate (aculeae about 1.0 µm, and usually less than 2.0 µm, in length; may be recurved or flared, e.g., see SEM in Head, 1997, fig. 17.14). Processes often narrow distally, just below process termination, and on some specimens are constricted also at base and elsewhere along process length. Processes usually closed distally. Annular thickenings (around two to six, number generally increasing with process length) developed on inner surface of process stems. Processes generally unbranched, but bifurcate processes occasionally developed on one or both lateral margins (Head, 1993, figs. 22.10, 23; Fig. 10.1; but not seen on holotype). Processes usually cover entire cyst but concentrated around ambitus. On Belgian specimens, processes show some alignment on or near plate boundaries, particularly along cingular margins and around third postcingular plate, but also occur randomly.
Tabulation also expressed on Belgian specimens by pale, narrow, sutural lines (presumably thinning of wall) developed variably over surface, evident particularly along cingulum and in area around archeopyle.
Archeopyle 2a intercalary, rounded outline, variably five-sided camerate, or six-sided linteloid; accessory sutures present. Hexa archeopyle contacts one apical (39), two intercalary (1a and 3a), and three precingular (30, 40, and 50) plates (Figs. 8.6–8.10, 9.5–9.9). Penta archeopyle contacts plates 39, 1a, 3a, 30, and 40 (Figs. 8.1–8.5, 8.11, 8.12, 9.1–9.4).
Hence, the penta geometry involves plate 40 contacting 3a (Figs. 8.1–8.5, 8.11, 8.12, 9.1–9.4). A penta geometry where plate 40 contacts plate 1a has not been observed.