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Pseudoceratium weymouthense
From Fensome et al., 2019:
Pseudoceratium weymouthense Helby, 1987, p.316–317, figs.19A–C,20A–D. Holotype: Helby, 1987, figs.19A–B; Fensome et al., 1996, figs.1–2 — p.2443; Fensome et al., 2019a, figs.19S–T. Age: late Tithonian–early Berriasian.
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Original description: Helby, 1987, p. 316-317
Proximate cysts, compressed ceratioid with large apical horn, a long antapical horn and very long, postcingular horn. Cyst body distorted towards the right side by extension of the paracingulum onto the anterior part of the postcingular horn. Cyst wall 2-layered, comprised of autophragm and ectophragm, although in some areas ectocoel not apparent. Autophragm smooth, about 1 µm thick . Ectophragm apparently continuous, less than 1µm thick, surface appearance reticulate. Processes between wall layers 0.5-1.5 µm long, 0.5 µm wide, 1-2 µm; apart and irregularly distributed although they are slightly longer and more closely packed in pandasutural regions. Paratabulation indicated mainly by principal and accessory archeopyle sutures and less so by greater length of processes within the ectocoel in pandasutural areas, particularly those on epicyst. Formula not fully determined. Archeopyle apical type [tA], principal archeopyle suture zigzag, parasulcal notch offset to left ventral position. Operculum normally free. Paracingulum indicated by a distinct, equatorial protrusion on the left side and discerned on some specimens as subparallel areas curving across dorsal surface to distinct cingular notches on the anterior part of the postcingular horn. Extension of paracingulum onto the horn causing an eccentricity towards the right side of the cyst. Parasulcus not well defined on the hypocyst but twisting from left ventral position on the epicyst to midventral position on the hypocyst. Measurements. See Fig. 18 for key to measurements. Twenty-five specimens from Cape Weymouth-2 at 154 m, in the P. iehiense Zone. were measured as:-- A, 95(129)170 µm; B,68(81)97 µm; C, 195(231)253 µm; D, 42(58)82 µm.
Affinities:
Helby, 1987, p. 317: Pseudoceratium weymouthense differs from P. iehiense in being larger and in having much longer horns. Pseudoceratium weymouthense superficially resembles P. nudum Gocht 1957 but has much longer horns and a larger, eccentric cyst body with holocavation. Pseudoceratium weymouthense resembles the theca of the extant species Ceratium carolinianum (Bailey) Jorgens÷n 1911, as illustrated by Wall & Evitt (1975, text-fig.5).
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Comments Fensome et al., 2019a:
This species is clearly distinguished by long apical, lateral, and antapical horns and an irregular “bubbly” reticulum, apparently formed by the periphragm. Helby (1987, p. 316) noted that the cyst wall is two-layered and composed of:
"… autophragm and ectophragm [i.e. endophragm and periphragm in our terminology], although in some areas ectocoel not apparent …. Ectophragm apparently continuous … [its] surface … reticulate. Processes between wall layers … irregularly distributed although … slightly longer and more closely packed in pandasutural regions."
From the illustrations of Helby (1987), the pericoel is barely discernable and the wall surface resembles that typical of Nyktericysta, albeit with coarser ornament. See also comments under Pseudoceratium toveae.
Stratigraphical occurrence. Helby (1987) recorded Pseudoceratium weymouthense from the upper Tithonian to lower Berriasian of Queensland, Australia.
Pseudoceratium weymouthense Helby, 1987, p.316–317, figs.19A–C,20A–D. Holotype: Helby, 1987, figs.19A–B; Fensome et al., 1996, figs.1–2 — p.2443; Fensome et al., 2019a, figs.19S–T. Age: late Tithonian–early Berriasian.
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Original description: Helby, 1987, p. 316-317
Proximate cysts, compressed ceratioid with large apical horn, a long antapical horn and very long, postcingular horn. Cyst body distorted towards the right side by extension of the paracingulum onto the anterior part of the postcingular horn. Cyst wall 2-layered, comprised of autophragm and ectophragm, although in some areas ectocoel not apparent. Autophragm smooth, about 1 µm thick . Ectophragm apparently continuous, less than 1µm thick, surface appearance reticulate. Processes between wall layers 0.5-1.5 µm long, 0.5 µm wide, 1-2 µm; apart and irregularly distributed although they are slightly longer and more closely packed in pandasutural regions. Paratabulation indicated mainly by principal and accessory archeopyle sutures and less so by greater length of processes within the ectocoel in pandasutural areas, particularly those on epicyst. Formula not fully determined. Archeopyle apical type [tA], principal archeopyle suture zigzag, parasulcal notch offset to left ventral position. Operculum normally free. Paracingulum indicated by a distinct, equatorial protrusion on the left side and discerned on some specimens as subparallel areas curving across dorsal surface to distinct cingular notches on the anterior part of the postcingular horn. Extension of paracingulum onto the horn causing an eccentricity towards the right side of the cyst. Parasulcus not well defined on the hypocyst but twisting from left ventral position on the epicyst to midventral position on the hypocyst. Measurements. See Fig. 18 for key to measurements. Twenty-five specimens from Cape Weymouth-2 at 154 m, in the P. iehiense Zone. were measured as:-- A, 95(129)170 µm; B,68(81)97 µm; C, 195(231)253 µm; D, 42(58)82 µm.
Affinities:
Helby, 1987, p. 317: Pseudoceratium weymouthense differs from P. iehiense in being larger and in having much longer horns. Pseudoceratium weymouthense superficially resembles P. nudum Gocht 1957 but has much longer horns and a larger, eccentric cyst body with holocavation. Pseudoceratium weymouthense resembles the theca of the extant species Ceratium carolinianum (Bailey) Jorgens÷n 1911, as illustrated by Wall & Evitt (1975, text-fig.5).
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Comments Fensome et al., 2019a:
This species is clearly distinguished by long apical, lateral, and antapical horns and an irregular “bubbly” reticulum, apparently formed by the periphragm. Helby (1987, p. 316) noted that the cyst wall is two-layered and composed of:
"… autophragm and ectophragm [i.e. endophragm and periphragm in our terminology], although in some areas ectocoel not apparent …. Ectophragm apparently continuous … [its] surface … reticulate. Processes between wall layers … irregularly distributed although … slightly longer and more closely packed in pandasutural regions."
From the illustrations of Helby (1987), the pericoel is barely discernable and the wall surface resembles that typical of Nyktericysta, albeit with coarser ornament. See also comments under Pseudoceratium toveae.
Stratigraphical occurrence. Helby (1987) recorded Pseudoceratium weymouthense from the upper Tithonian to lower Berriasian of Queensland, Australia.