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Impagidinium diaphanum
Impagidinium? diaphanum sp. nov. , Zorzi, C. et al., 264, 24–37, 2019
Holotype: Zorzi, C. et al., 2019, Sample ODP 887C-14H3W, Plate III, 1–7
Age: Pliocene
Stratigraphic range: Early Pliocene, from 4.43 to 3.58 Ma.
Original description: Zorzi, C. et al., 2019: Impagidinium? diaphanum sp. nov.:
Diagnosis:
A proximate, delicate, suturocavate species with spheroidal central body. Low and pronounced cavate septa of even height are appressed distally to form straight to slightly undulating crests. The surface of the central body and septa is finely granulate. Septa clearly delimit the formula 3′–4′, 6′′, 6c, as, ps, 6′′′, 1p, 1′′′′. The anterior sulcul plate (as) contacts Plate 5′′. Plate 1′′′ is long and narrow, and the posterior sulcal plate is subrectangular. The ends of the cingulum are aligned to overhanging, and the dorsal tabulation shows approximately neutral torsion. The archeopyle, formed by loss of plate 3′′, is relatively small.
Description:
Cyst: proximate and suturocavate with large subspherical central body bearing low septa that fully reflect tabulation.
Central body wall: is thin (~ 0.2–0.3μm) away from the sutures, stratification is indistinguishable under light microscopy.
The surface of the central body and sutures is finely and faintly granulate, with adjacent granules often fused. Septa are low, continuous, pronounced, cavate and distally appressed, with smooth to slightly undulating crests, and are of approximately even height over the cyst.
Tabulation: Septa follow the formula 3′ or 4′, 6′′, 6c, as, ps, 6′′′, 1p and 1′′′′. Apical plates 1′ and 4′ may be merged, but plates are otherwise clearly delimited by well-expressed septa. Plate 6′′ is short owing to the distinctive contact between the anterior sulcal plate and plate 5′′. Dorsal tabulation shows neutral torsion. Ventral organization is S-type, with the ends of the cingulum aligned to overhanging. The cingulum may narrow slightly at boundaries between adjacent cingular plates on the dorsal surface. Anterior and posterior sulcal plates are distinct, and other sulcal plates may be weakly expressed. Also distinct is the long and narrow postcingular plate 1′′′
which contacts both the cingulum and anterior sulcal plate and extends to plate 1p (Plate III, 1, 7, 8). The posterior sulcal plate is subrectangular.
Archeopyle: formed by loss of plate 3′′, has well-defined angles, corresponds closely to the bounding septa, and is relatively small relative to the total length of the cyst.
Dimensions:
Holotype: central body length 43 μm; height of septa 1.7 μm; total length 46 μm.
Range based on Hole 882A - 4 specimens measured: central body maximum diameter 36 (49.3) 60 μm; height of septa 0.5 (1.0) 1.3 μm; total length 38 (52) 65 μm
Range based on Hole 887C - 4 specimens measured: central body maximum diameter 39 (43.0) 48 μm; height of septa 1.0 (1.3) 1.7 μm; total length 42 (45.25) 50 μm
Remarks: The presence of a long and narrow 1′′′ plate is a particularly diagnostic feature of this species. The assignment to Impagidinium is considered questionable owing to the contact between the anterior sulcal plate (as) and the fifth precingular plate (5′′) in the few specimens (including the holotype) where this detail has been observed, in contrast to the narrow contact between 6′′ and the apical plate series as diagnosed for the genus (Stover and Evitt, 1978). Observations of additional material will be needed to determine whether this unusual topology is a consistent feature of this species.
Affinities: Impagidinium? diaphanum sp. nov., is recognizable by its thin central body wall, well expressed tabulation, as/5′′ contact, distinctive long, narrow plate 1′′′, intratabular transparency, and clarity of the sutures. This species is distinguished from all others of the genus Impagidinium by its relatively large size, thin central body wall, low but relatively rigid and pronounced cavate sutural crests that express the tabulation relatively completely.
Only Impagidinium pallidum (Bujak, 1984) also has an extremely thin central body wall and low crests (~ 3–4 μm according to Rochon et al., 1999; not 5–10 μm as reported in Bujak, 1984) of even height. However, the crests are narrow and delicate and difficult to distinguish from folds in the central body wall
when the cysts are crumpled.
Holotype: Zorzi, C. et al., 2019, Sample ODP 887C-14H3W, Plate III, 1–7
Age: Pliocene
Stratigraphic range: Early Pliocene, from 4.43 to 3.58 Ma.
Original description: Zorzi, C. et al., 2019: Impagidinium? diaphanum sp. nov.:
Diagnosis:
A proximate, delicate, suturocavate species with spheroidal central body. Low and pronounced cavate septa of even height are appressed distally to form straight to slightly undulating crests. The surface of the central body and septa is finely granulate. Septa clearly delimit the formula 3′–4′, 6′′, 6c, as, ps, 6′′′, 1p, 1′′′′. The anterior sulcul plate (as) contacts Plate 5′′. Plate 1′′′ is long and narrow, and the posterior sulcal plate is subrectangular. The ends of the cingulum are aligned to overhanging, and the dorsal tabulation shows approximately neutral torsion. The archeopyle, formed by loss of plate 3′′, is relatively small.
Description:
Cyst: proximate and suturocavate with large subspherical central body bearing low septa that fully reflect tabulation.
Central body wall: is thin (~ 0.2–0.3μm) away from the sutures, stratification is indistinguishable under light microscopy.
The surface of the central body and sutures is finely and faintly granulate, with adjacent granules often fused. Septa are low, continuous, pronounced, cavate and distally appressed, with smooth to slightly undulating crests, and are of approximately even height over the cyst.
Tabulation: Septa follow the formula 3′ or 4′, 6′′, 6c, as, ps, 6′′′, 1p and 1′′′′. Apical plates 1′ and 4′ may be merged, but plates are otherwise clearly delimited by well-expressed septa. Plate 6′′ is short owing to the distinctive contact between the anterior sulcal plate and plate 5′′. Dorsal tabulation shows neutral torsion. Ventral organization is S-type, with the ends of the cingulum aligned to overhanging. The cingulum may narrow slightly at boundaries between adjacent cingular plates on the dorsal surface. Anterior and posterior sulcal plates are distinct, and other sulcal plates may be weakly expressed. Also distinct is the long and narrow postcingular plate 1′′′
which contacts both the cingulum and anterior sulcal plate and extends to plate 1p (Plate III, 1, 7, 8). The posterior sulcal plate is subrectangular.
Archeopyle: formed by loss of plate 3′′, has well-defined angles, corresponds closely to the bounding septa, and is relatively small relative to the total length of the cyst.
Dimensions:
Holotype: central body length 43 μm; height of septa 1.7 μm; total length 46 μm.
Range based on Hole 882A - 4 specimens measured: central body maximum diameter 36 (49.3) 60 μm; height of septa 0.5 (1.0) 1.3 μm; total length 38 (52) 65 μm
Range based on Hole 887C - 4 specimens measured: central body maximum diameter 39 (43.0) 48 μm; height of septa 1.0 (1.3) 1.7 μm; total length 42 (45.25) 50 μm
Remarks: The presence of a long and narrow 1′′′ plate is a particularly diagnostic feature of this species. The assignment to Impagidinium is considered questionable owing to the contact between the anterior sulcal plate (as) and the fifth precingular plate (5′′) in the few specimens (including the holotype) where this detail has been observed, in contrast to the narrow contact between 6′′ and the apical plate series as diagnosed for the genus (Stover and Evitt, 1978). Observations of additional material will be needed to determine whether this unusual topology is a consistent feature of this species.
Affinities: Impagidinium? diaphanum sp. nov., is recognizable by its thin central body wall, well expressed tabulation, as/5′′ contact, distinctive long, narrow plate 1′′′, intratabular transparency, and clarity of the sutures. This species is distinguished from all others of the genus Impagidinium by its relatively large size, thin central body wall, low but relatively rigid and pronounced cavate sutural crests that express the tabulation relatively completely.
Only Impagidinium pallidum (Bujak, 1984) also has an extremely thin central body wall and low crests (~ 3–4 μm according to Rochon et al., 1999; not 5–10 μm as reported in Bujak, 1984) of even height. However, the crests are narrow and delicate and difficult to distinguish from folds in the central body wall
when the cysts are crumpled.