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Thalassiphora robusta
Thalassiphora robusta Smith and Harding, 2004, p.376–377, pl.5, figs.1–3,12.
Holotype: Smith and Harding, 2004, pl.5, figs.1–2.
Age: middle Volgian.
Original description (Smith and Harding, 2004):
Thalassiphora? robusta Smith and Harding, sp. nov. (Plate V, 1–3,12).
Holotype: Slide U3/2, England Finder coordinates J41. Sedgwick Museum number X.39377 ( Plate V, 1,2).
Type locality: Gorodische section, Volga Basin.
Type horizon: Bed 2 (sample U3), mudstone, Middle Volgian, Zaraiskites zarajskensis Subzone.
Range: Mid-Volgian, restricted to the Zaraiskites zarajskensis Subzone at both Volga Basin localities (see Fig. 8).
Etymology: named after the thick and robust nature of the periphragm.
Diagnosis: large subspherical to ovoidal camocavate cysts, with gonyaulcacean tabulation. The periphragm is thick and fibrous or spongy, endophragm is smooth and bears a short solid apical horn. Wall layers are adpressed on the dorsal surface, but elsewhere are separated by a significant cavation. The archeopyle is Type P3″.
Description: large subspherical to ovoidal cavate cysts. The cysts are slightly dorso-ventrally compressed. The periphragm is thick and fibrous or spongy and adpressed to the endophragm on the dorsal surface. The endophragm is smooth and robust. The apex of the endophragm generally bears a short solid horn, the antapex is always rounded. The archeopyle is located immediately below the apical horn. Although Tabulation appears somewhat cryptic in light microscopy, save for the archeopyle, which is of slightly variable size and shape (and is almost certainly Type P3″), a gonyaulacacean tabulation is indicated in SEM observations, which reveal indistinct sutures in the form of broad slightly elevated/wrinkled areas of periphragm (Plate V, 12).
Dimensions: periphragm: length (72) 89 (153) μm, width (70) 93 (130) μm; endophragm: length (34) 50 (72) μm, width (38) 52 (73) μm.
Remarks: this species is tentatively placed in Thalassiphora Eisenack and Gocht emend. Benedek and Gocht 1981. However, it lacks the characteristic dorsal ‘keel’ or periphragmal fold of this genus, and in addition possesses a horn on the endophragm not typically found on the other species of this genus. It cannot be placed in Membranilarnacia Eisenack emend. Williams and Downie 1966 since it lacks processes supporting the outer wall layer. T.? robusta is superficially similar to Pareodinia halosa Filatoff emend. Prauss 1989. However, it clearly possesses two wall layers with an outer periphragm rather than a kalyptra.
Holotype: Smith and Harding, 2004, pl.5, figs.1–2.
Age: middle Volgian.
Original description (Smith and Harding, 2004):
Thalassiphora? robusta Smith and Harding, sp. nov. (Plate V, 1–3,12).
Holotype: Slide U3/2, England Finder coordinates J41. Sedgwick Museum number X.39377 ( Plate V, 1,2).
Type locality: Gorodische section, Volga Basin.
Type horizon: Bed 2 (sample U3), mudstone, Middle Volgian, Zaraiskites zarajskensis Subzone.
Range: Mid-Volgian, restricted to the Zaraiskites zarajskensis Subzone at both Volga Basin localities (see Fig. 8).
Etymology: named after the thick and robust nature of the periphragm.
Diagnosis: large subspherical to ovoidal camocavate cysts, with gonyaulcacean tabulation. The periphragm is thick and fibrous or spongy, endophragm is smooth and bears a short solid apical horn. Wall layers are adpressed on the dorsal surface, but elsewhere are separated by a significant cavation. The archeopyle is Type P3″.
Description: large subspherical to ovoidal cavate cysts. The cysts are slightly dorso-ventrally compressed. The periphragm is thick and fibrous or spongy and adpressed to the endophragm on the dorsal surface. The endophragm is smooth and robust. The apex of the endophragm generally bears a short solid horn, the antapex is always rounded. The archeopyle is located immediately below the apical horn. Although Tabulation appears somewhat cryptic in light microscopy, save for the archeopyle, which is of slightly variable size and shape (and is almost certainly Type P3″), a gonyaulacacean tabulation is indicated in SEM observations, which reveal indistinct sutures in the form of broad slightly elevated/wrinkled areas of periphragm (Plate V, 12).
Dimensions: periphragm: length (72) 89 (153) μm, width (70) 93 (130) μm; endophragm: length (34) 50 (72) μm, width (38) 52 (73) μm.
Remarks: this species is tentatively placed in Thalassiphora Eisenack and Gocht emend. Benedek and Gocht 1981. However, it lacks the characteristic dorsal ‘keel’ or periphragmal fold of this genus, and in addition possesses a horn on the endophragm not typically found on the other species of this genus. It cannot be placed in Membranilarnacia Eisenack emend. Williams and Downie 1966 since it lacks processes supporting the outer wall layer. T.? robusta is superficially similar to Pareodinia halosa Filatoff emend. Prauss 1989. However, it clearly possesses two wall layers with an outer periphragm rather than a kalyptra.