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Barssidinium graminosum
Barssidinium graminosum, Lentin et al., 1994
Holotype: Lentin et al., 1994, pl.2, fig.11
Paratypes: Lentin et al., 1994, pl.2, fig.9, 12
Locus typicus: Amoco Imperial Heron H-73 well, Grand Banks, offshore Canada
Stratum typicum: Late Miocene
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Original description: [Lentin et al., 1994, p. 579]:
Diagnosis:
A species of Barssidinium in which the processes are slender, hollow to partly solid, distally closed, bifid or furcate. Process length about one third to one fifth of the length of the central body.
Description:
Shape: Subovoidal to rounded pentagonal to peridinioid. Cyst weakly to strongly dorsoventrally compressed, ambitus subcircular, suboval, rounded pentagonal to peridinioid. Apex rounded; antapex rounded to weakly bilobate. Epicyst and hypocyst appear to be more or less equal in size.
Wall relationships: Usually acavate with autophragm only; rarely circumcavate, with periphragm and endophragm narrowly separated.
Wall features: Periphragm or autophragm smooth, generally laevigate, occasionally sparsely granulate. Processes predominantly marginate, long, slender, hollow to partly solid, distally closed, bifid to furcate and occasionally branched; they commonly have annular thickenings (or septa). Process length about one third to one fifth of the length of the central body and with a length-to-breadth ratio of about 15:1.
Mode of excystment: Usually involves the loss of a large hexa isodeltaform middorsal intercalary paraplate, presumably 2a, posteriorly extending almost to the equator of the cyst. The operculum is usually free, but may be adnate anteriorly. Rarely, accessory archeopyle sutures between paraplates adjacent to 2a appear to develop and a second intercalary paraplate may be dislodged. When two wall layers are observed, they appear fused on the operculum.
Paratabulation: Generally indicated by archeopyle only and presumed to be peridinialean; occasional alignment of processes suggests a paracingulum and possibly other parasutures. Parasulcus not identified.
Dimensions/Size:
Holotype: body length 86 µm, body width 81 µm, length of processes up to 23 µm.
Range: body length 63(85)92 µm (8 specimens), body width 58(71)81 µm (8 specimens), maximum length of processes 13(19)25 µm (8 specimens).
Affinities:
Barssidinium wrennii, Barssidinium evangelineae, and Barssidinium graminosum are differentiated on the basis of the processes. Both B. wrennii and B. graminosum differ from B. evangelineae in having distally closed, furcate processes, in contrast to the distally open, aculeate processes of B. evangelineae. The length of the processes in B. wrennii and B. graminosum is different: in B. wrennii the process length is about one sixth to one eighth of the length of the central body; in B. graminosum, the process length is about one third to one fifth of the length of the central body. Although the process length in B. evangelineae is typically shorter than that in B. wrennii, there is some overlap.
Holotype: Lentin et al., 1994, pl.2, fig.11
Paratypes: Lentin et al., 1994, pl.2, fig.9, 12
Locus typicus: Amoco Imperial Heron H-73 well, Grand Banks, offshore Canada
Stratum typicum: Late Miocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Lentin et al., 1994, p. 579]:
Diagnosis:
A species of Barssidinium in which the processes are slender, hollow to partly solid, distally closed, bifid or furcate. Process length about one third to one fifth of the length of the central body.
Description:
Shape: Subovoidal to rounded pentagonal to peridinioid. Cyst weakly to strongly dorsoventrally compressed, ambitus subcircular, suboval, rounded pentagonal to peridinioid. Apex rounded; antapex rounded to weakly bilobate. Epicyst and hypocyst appear to be more or less equal in size.
Wall relationships: Usually acavate with autophragm only; rarely circumcavate, with periphragm and endophragm narrowly separated.
Wall features: Periphragm or autophragm smooth, generally laevigate, occasionally sparsely granulate. Processes predominantly marginate, long, slender, hollow to partly solid, distally closed, bifid to furcate and occasionally branched; they commonly have annular thickenings (or septa). Process length about one third to one fifth of the length of the central body and with a length-to-breadth ratio of about 15:1.
Mode of excystment: Usually involves the loss of a large hexa isodeltaform middorsal intercalary paraplate, presumably 2a, posteriorly extending almost to the equator of the cyst. The operculum is usually free, but may be adnate anteriorly. Rarely, accessory archeopyle sutures between paraplates adjacent to 2a appear to develop and a second intercalary paraplate may be dislodged. When two wall layers are observed, they appear fused on the operculum.
Paratabulation: Generally indicated by archeopyle only and presumed to be peridinialean; occasional alignment of processes suggests a paracingulum and possibly other parasutures. Parasulcus not identified.
Dimensions/Size:
Holotype: body length 86 µm, body width 81 µm, length of processes up to 23 µm.
Range: body length 63(85)92 µm (8 specimens), body width 58(71)81 µm (8 specimens), maximum length of processes 13(19)25 µm (8 specimens).
Affinities:
Barssidinium wrennii, Barssidinium evangelineae, and Barssidinium graminosum are differentiated on the basis of the processes. Both B. wrennii and B. graminosum differ from B. evangelineae in having distally closed, furcate processes, in contrast to the distally open, aculeate processes of B. evangelineae. The length of the processes in B. wrennii and B. graminosum is different: in B. wrennii the process length is about one sixth to one eighth of the length of the central body; in B. graminosum, the process length is about one third to one fifth of the length of the central body. Although the process length in B. evangelineae is typically shorter than that in B. wrennii, there is some overlap.