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Impagidinium sekadensis
Impagidinium sekadensis sp. nov.; Slimani, H. et al. 2021
Holotype: Sample SK5, slide 2, England Finder (EF) coordinates G47/2 (Plate IIA–C); Slimani, H. et al. 2021
Age: upper Campanian
Original description: Slimani, H. et al. 2021: Impagidinium sekadensis sp. nov.:
Diagnosis:
Ovoid to rhomboidal and smooth-walled Impagidinium characterized by smooth, rigid and well-developed sutural septa with entire distal margins, by large apical (2′, 3′) plates and very small longitudinal apical (1′, 4′) plates, which are rarely separated (partially) by a discontinuous sutural septum. Sulcus narrow and untabulated with the
exception of the posterior sulcal plate ps, which is delimited by sutural septa.
Description:
The species is of intermediate to large size, acavate and proximate to proximochorate with a subspheroidal to ovoid central body.
Cyst wall: consists of a smooth and thin autophragm (0.5–1 μm thick), giving rise to sutural septa. Septa are rigid and high (5–11 μm) with entire and straight to slightly convex distal margins.
Tabulation: indicated gonyaulacoid tabulation, typical of the genus Impagidinium: 4′, 6′′, 6c, 5′′′, 1p, 1′′′′, ps. Apical plates 2′ and 3′ are large (Plate IIF–H), however 1′ and 4′ are often represented by a narrow subrectangular plate, or rarely separated (partially) by a discontinuous sutural septum. The ventral plate arrangement suggests, in combination with the strongly laevorotatore cingulum (Plate IIA, D), an “S-type ventral organization” characterizing the Spiniferites complex (Evitt, 1985). The precingular plate 6′′ is small compared to the other precingular plates and subtriangular (Plate IIA, D) and has a very short contact with only one apical plate (4′) (Plate IIL). The sulcus is narrow, also bordered by sutural septa and subdivided only in its posterior part, with a posterior sulcal plate ps delimited by sutural septa (Plate IIA, D, H). No
other sulcal plates are observed. The postcingular plate 1′′′ is undifferentiated and may be included in the sulcus, and only 5 postcingular plates (2′′′–6′′′) are delimited by parasutural septa. The postcingular plate 2′′′ does not have a contact with the antapical plate 1′′′′ and also the posterior sulcal plate ps does not contact the postcingular plate 5′′′ (Plate IID, H). The antapical plate 1′′′′ is subhexagonal and forms a sexiform hypocystal plate arrangement with the posterior intercalary 1p, the posterior sulcal
ps and the postcingular plates 3′′', 4′′', 5′′', 6′′' (Plate IIA, D, H).
Archeopyle: precingular (type P), formed by release of precingular plate 3′′. The operculum is free.
Dimensions:
Range for 10 specimens measured: overall length 60 (63)70 μm, overall width 50(64)70 μm, height of septa 5–11 μm.
Holotype: overall length 65 μm, overall width 75 μm, height of septa 8–10 μm.
Paratype: overall length 65 μm, overall width 58 μm, height of septa 6–11 μm.
Affinities:
Impagidinium sekadensis differs from all the other species of Impagidinium by the combination of a smooth central body wall, smooth, rigid and well-developed sutural septa with entire and slightly convex distal margins, large apical (2′, 3′) plates and narrow longitudinal apical (1′, 4′) plates and a narrow sulcus with a sol plate (ps) delimited by sutural septa.
The new species differs from Impagidinium patulum (Wall, 1967) Stover and Evitt 1978 by the fact that all its plates are delimited by sutural septa, however in Impagidinium patulum, the sutural septa between the precingular plate 6′′ and sulcus, the cingular plate 1c and the postcingular 2′′′, and between the cingular plate 6c and the postcigular 6′′′ are absent.
Impagidinium sekadensis resembles Impagidinium cristatum (May, 1980) Lentin and Williams, 1981 by its smooth sutural septa and central body wall, its well-expressed tabulation and its sulcus subdivided only in its posterior part, but it is distinguished by its larger size and its higher septa with convex rather than depressed distal margins. Sutural septa in Impagidinium velorum Bujak, 1984 are two times higher than in the new species and the tabulation is difficult to determine.
Holotype: Sample SK5, slide 2, England Finder (EF) coordinates G47/2 (Plate IIA–C); Slimani, H. et al. 2021
Age: upper Campanian
Original description: Slimani, H. et al. 2021: Impagidinium sekadensis sp. nov.:
Diagnosis:
Ovoid to rhomboidal and smooth-walled Impagidinium characterized by smooth, rigid and well-developed sutural septa with entire distal margins, by large apical (2′, 3′) plates and very small longitudinal apical (1′, 4′) plates, which are rarely separated (partially) by a discontinuous sutural septum. Sulcus narrow and untabulated with the
exception of the posterior sulcal plate ps, which is delimited by sutural septa.
Description:
The species is of intermediate to large size, acavate and proximate to proximochorate with a subspheroidal to ovoid central body.
Cyst wall: consists of a smooth and thin autophragm (0.5–1 μm thick), giving rise to sutural septa. Septa are rigid and high (5–11 μm) with entire and straight to slightly convex distal margins.
Tabulation: indicated gonyaulacoid tabulation, typical of the genus Impagidinium: 4′, 6′′, 6c, 5′′′, 1p, 1′′′′, ps. Apical plates 2′ and 3′ are large (Plate IIF–H), however 1′ and 4′ are often represented by a narrow subrectangular plate, or rarely separated (partially) by a discontinuous sutural septum. The ventral plate arrangement suggests, in combination with the strongly laevorotatore cingulum (Plate IIA, D), an “S-type ventral organization” characterizing the Spiniferites complex (Evitt, 1985). The precingular plate 6′′ is small compared to the other precingular plates and subtriangular (Plate IIA, D) and has a very short contact with only one apical plate (4′) (Plate IIL). The sulcus is narrow, also bordered by sutural septa and subdivided only in its posterior part, with a posterior sulcal plate ps delimited by sutural septa (Plate IIA, D, H). No
other sulcal plates are observed. The postcingular plate 1′′′ is undifferentiated and may be included in the sulcus, and only 5 postcingular plates (2′′′–6′′′) are delimited by parasutural septa. The postcingular plate 2′′′ does not have a contact with the antapical plate 1′′′′ and also the posterior sulcal plate ps does not contact the postcingular plate 5′′′ (Plate IID, H). The antapical plate 1′′′′ is subhexagonal and forms a sexiform hypocystal plate arrangement with the posterior intercalary 1p, the posterior sulcal
ps and the postcingular plates 3′′', 4′′', 5′′', 6′′' (Plate IIA, D, H).
Archeopyle: precingular (type P), formed by release of precingular plate 3′′. The operculum is free.
Dimensions:
Range for 10 specimens measured: overall length 60 (63)70 μm, overall width 50(64)70 μm, height of septa 5–11 μm.
Holotype: overall length 65 μm, overall width 75 μm, height of septa 8–10 μm.
Paratype: overall length 65 μm, overall width 58 μm, height of septa 6–11 μm.
Affinities:
Impagidinium sekadensis differs from all the other species of Impagidinium by the combination of a smooth central body wall, smooth, rigid and well-developed sutural septa with entire and slightly convex distal margins, large apical (2′, 3′) plates and narrow longitudinal apical (1′, 4′) plates and a narrow sulcus with a sol plate (ps) delimited by sutural septa.
The new species differs from Impagidinium patulum (Wall, 1967) Stover and Evitt 1978 by the fact that all its plates are delimited by sutural septa, however in Impagidinium patulum, the sutural septa between the precingular plate 6′′ and sulcus, the cingular plate 1c and the postcingular 2′′′, and between the cingular plate 6c and the postcigular 6′′′ are absent.
Impagidinium sekadensis resembles Impagidinium cristatum (May, 1980) Lentin and Williams, 1981 by its smooth sutural septa and central body wall, its well-expressed tabulation and its sulcus subdivided only in its posterior part, but it is distinguished by its larger size and its higher septa with convex rather than depressed distal margins. Sutural septa in Impagidinium velorum Bujak, 1984 are two times higher than in the new species and the tabulation is difficult to determine.