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Areosphaeridium fenestratum
Areosphaeridium fenestratum, Bujak, 1976
Holotype: Bujak, 1976, pl.3, fig.2
Locus typicus: Barton Beds, Isle of Wight, England
Stratum typicum: Eocene
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Original description: [Bujak, 1976, p. 107]:
Diagnosis:
Central body dorsoventrally compressed, outline subcircular to subquadrate.
Autophragm scabrate to granulate, forming intratabular processes with solid, fibrous stems.
Processes distally bifurcate or branched, bearing platforms formed of interconnecting trabeculae. Platforms of adjacent processes sometimes connected by trabeculae.
Reflected process tabulation 4", 5", xc, 5""", 1p, 1""""; plate areas 6", 6""", anterior sulcal area, and middorsal and midventral areas without processes. Elsewhere one process per plate area, except near antapex where additional processes sometimes present, and on lateral cingular margins where four to nine processes always present.
Archeopyle apical, tetratabular. Operculum simple and usually detached. Short accessory archeopyle sutures often partially defining six precingular plate areas, and an anterior sulcal plate area offset to the left on the ventral surface.
Dimensions:
Holotype, central body length (without operculum) 33 µm, central body breadth 41 µm, process length 16 µm.
Observed range, central body length (with operculum) 44 µm, central body length (without operculum) 28-42 µm, central body breadth 30-46 µm, process length 14-23 µm.
Affinities: (p. 109):
The process platforms on A. fenestratum are composed of interconnecting trabeculae which form either loose networks, or perforate membranes with openings of regular or irregular size and shape. Smaller, regular fenestrations are often concentrated along the platform margins, and larger, irregular fenestrations near the process stems. Adjacent process platforms are sometimes joined by trabeculae, particularly those near the antapex. The process platforms also vary in shape and may have either entire or ragged margins.
The resemblance of the process platforms on A. fenestratum to those on A. diktyoplokus give the two species a similar appearance, but detailed comparison of the overall morphology of these species indicates a number of differences. A. diktyoplokus has a spherical to subspherical central body which is not flattened dorsoventrally, whereas the central body of A. fenestratum is typically flattened dorsoventrally with subcircular to subquadrate outline. The process platforms on specimens of A. diktyoplokus from the Barton Beds have entire margins and regularly ordered fenestrations. Only a few specimens of A. fenestratum from the Middle and Upper Barton Beds possess similar platforms, and the earliest representatives of A. fenestratum, from the Lower Barton Beds, invariably have
platforms with ragged margins and irregular fenestrations (Plate II, 9). On A. diktyoplokus, the processes reflect a tabulation of 4", 6", 5-6""", 0-1p, 1"""", with one or two extremely slender cingular processes rarely present on the cingular zone. On A. fenestratum, processes are always present on the lateral margins of the cingular zone and on the posterior intercalary plate area, with additional processes
often present between the posterior intercalary and antapical processes. Unlike A. diktyoplokus, A. fenestratum never has processes on plate areas 6"" and 6""" . The mean dimensions of central body and overall length and breadth are distinctly smaller for A. fenestratum than for A. diktyoplokus.
A. multicornutum lacks the distinctive process platforms which characterize A. fenestratum, but is identical in all other morphological details. Both have dorsoventrally flattened central bodies of similar outline and a sulcal notch offset to the left on the ventral surface. The processes on both species are solid, finely fibrous and reflect a tabulation of 4", 5", xc, 5""", 1p, 1"""", with additional processes
often present between the posterior intercalary and antapical processes. Accessory archeopyle sutures indicate the presence of a sixth precingular and an anterior sulcal plate area, although they do not bear processes.
Holotype: Bujak, 1976, pl.3, fig.2
Locus typicus: Barton Beds, Isle of Wight, England
Stratum typicum: Eocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Bujak, 1976, p. 107]:
Diagnosis:
Central body dorsoventrally compressed, outline subcircular to subquadrate.
Autophragm scabrate to granulate, forming intratabular processes with solid, fibrous stems.
Processes distally bifurcate or branched, bearing platforms formed of interconnecting trabeculae. Platforms of adjacent processes sometimes connected by trabeculae.
Reflected process tabulation 4", 5", xc, 5""", 1p, 1""""; plate areas 6", 6""", anterior sulcal area, and middorsal and midventral areas without processes. Elsewhere one process per plate area, except near antapex where additional processes sometimes present, and on lateral cingular margins where four to nine processes always present.
Archeopyle apical, tetratabular. Operculum simple and usually detached. Short accessory archeopyle sutures often partially defining six precingular plate areas, and an anterior sulcal plate area offset to the left on the ventral surface.
Dimensions:
Holotype, central body length (without operculum) 33 µm, central body breadth 41 µm, process length 16 µm.
Observed range, central body length (with operculum) 44 µm, central body length (without operculum) 28-42 µm, central body breadth 30-46 µm, process length 14-23 µm.
Affinities: (p. 109):
The process platforms on A. fenestratum are composed of interconnecting trabeculae which form either loose networks, or perforate membranes with openings of regular or irregular size and shape. Smaller, regular fenestrations are often concentrated along the platform margins, and larger, irregular fenestrations near the process stems. Adjacent process platforms are sometimes joined by trabeculae, particularly those near the antapex. The process platforms also vary in shape and may have either entire or ragged margins.
The resemblance of the process platforms on A. fenestratum to those on A. diktyoplokus give the two species a similar appearance, but detailed comparison of the overall morphology of these species indicates a number of differences. A. diktyoplokus has a spherical to subspherical central body which is not flattened dorsoventrally, whereas the central body of A. fenestratum is typically flattened dorsoventrally with subcircular to subquadrate outline. The process platforms on specimens of A. diktyoplokus from the Barton Beds have entire margins and regularly ordered fenestrations. Only a few specimens of A. fenestratum from the Middle and Upper Barton Beds possess similar platforms, and the earliest representatives of A. fenestratum, from the Lower Barton Beds, invariably have
platforms with ragged margins and irregular fenestrations (Plate II, 9). On A. diktyoplokus, the processes reflect a tabulation of 4", 6", 5-6""", 0-1p, 1"""", with one or two extremely slender cingular processes rarely present on the cingular zone. On A. fenestratum, processes are always present on the lateral margins of the cingular zone and on the posterior intercalary plate area, with additional processes
often present between the posterior intercalary and antapical processes. Unlike A. diktyoplokus, A. fenestratum never has processes on plate areas 6"" and 6""" . The mean dimensions of central body and overall length and breadth are distinctly smaller for A. fenestratum than for A. diktyoplokus.
A. multicornutum lacks the distinctive process platforms which characterize A. fenestratum, but is identical in all other morphological details. Both have dorsoventrally flattened central bodies of similar outline and a sulcal notch offset to the left on the ventral surface. The processes on both species are solid, finely fibrous and reflect a tabulation of 4", 5", xc, 5""", 1p, 1"""", with additional processes
often present between the posterior intercalary and antapical processes. Accessory archeopyle sutures indicate the presence of a sixth precingular and an anterior sulcal plate area, although they do not bear processes.