Back
Jansonia jurassica
From Fensome et al., 2019:
Jansonia jurassica Pocock, 1972, p.97–98, pl.29, figs.8–9; text-figs.14–15. Holotype: Pocock, 1972, pl.29, fig.8; Jansonius, 1986, pl.3, figs.4–6. Age: late Bajocian.
---------------------------------------------------------------------------------------------------
Locus typicus: Tidewater Eastern Crown, W Canada
Stratum typicum: Late Bajocian
Original description: Pocock, 1972, p.97
Vesicle small; more or less isodiametric; pear-shaped in outline; epitheca terminated by a smoothly rounded hollow apical horn about 10.0 Ám long which is only very rarely preserved (seen on only one of over two hundred specimens examined); hypotheca hemispherical; smooth; no antapical processes developed; transverse furrow about 6.0 µm wide; parallel-sided; slightly helicoidal; longitudinal furrow rarely seen; sutures reflected onto surface of vesicle of some specimens as very faint lines of minute granules; invisible on others; tabulation impossible to determine from any one specimen; partial tabulation, determined from several grains, appears to be (?'), 6'', 6g, 6''', 1P, 1''''; archeopyle apical with simple free operculum; vesicle two-layered; capsule less than 0.25 µm thick; smooth; tightly appressed to outer layer; outer layer 0.5-1.0 µm thick; surface finely and closely granulose; colour brown; length 25.0 (33.0) 40.0 µm (excluding apical horn); width 23.0 (33.0) 43.0 µm.
Supplemental description: Jansonius, 1986, p.211
(Holotype) 37 x 37 µm, dorsal side up (4" in the center); characteristically brown and leathery in appearance, wall thinning and becoming nearly colorless along the apical archeopyle; often darker in the region of the cingulum. The cingulum (6-8 µm wide) is distinctly delineated by two ridges; the displacement of the cingulum on the ventral side is very slight. Precingular plates are indicated by small acccessory sutures; however, it is difficult to discern their number (apparently six). No more than a few vague ridges delineating postcingulars can be observed. The whole surface of the grain is covered with a sculpture of low, often interrupted, wandering ridges that form a shallow incomplete reticulum; muri, and grooves (or brochi) between them, about 0.4-0.5 µm wide; wall, including sculpture, about 0.8-0.9 µm thick (thinner near apex). At low power the sculpture appears as granulation, possibly because the muri are uneven in height and bulk. (In other specimens the sculpture actually may be reduced to scattered granules.) It is characteristic of the preservation that many random cracks occur in the cyst, especially in the hypocyst, which do not seem to coincide with any paratabulation.
Remarks. Some hundred specimens have been seen by me, and a few appear to have a small thin apical operculum attached to one of the precingulars. No specimens have been observed showing the apical horn mentioned by Pocock. The one specimen from which it was described is lost, and was not photographed; thus it seems possible that abnormal development, or extraneous matter, may have been responsible for this appearance. The absence of paratabulation (other than incipient accessory precingular sutures and the distinct cingulum) is characteristic.
---------------------------------------------------------------------------------------------------
Emended description Vitacca et al., 2022:
(Plate XI, 1–6; Plate XII, 1)
1972 Jansonia jurassica Pocock, p. 97–98
Holotype: Pocock, 1972, p. 97, pl. 29, 8., Jansonius, 1986, pl. 3, 4–6.
Diagnosis: A pear-shaped species of Jansonia with a short, narrow epicyst and a larger, well-rounded hypocyst. Autophragm granulate, verrucate or rugulate. Low-relief crests indicate gonyaulacalean tabulation and combination archeopyle; operculum free.
Description: A small, sub-ovoidal to pear-shaped dinoflagellate cyst that is characteristically brown to dark brown, generally darkest around the cingulum, and lightest in colour apically. Epicyst shorter and narrower than hypocyst, which is antapically rounded. The cyst lacks any horns or protuberances. Autophragm thick, granulate or faintly verrucate and rugulate. Ornamental elements often fused to form sutural ridges, usually more pronounced antapically. The cingulum is generally well defined, weakly laevorotatory, ps prominent, widening antapically. Hypocystal tears are common. Inferred tabulation formula:? pr,?4′,?3–5a,?6–7″, 6c, 6″’, 1p, 1″”,?5–6s (Fig. 11A, A`). Archeopyle combination apical and anterior intercalary, type (tAtI), operculum free, the margin is often jagged or torn.
Dimensions: (23 specimens measured)
Length: 18 (23) 31
Width: 16 (21) 26
Remarks: The original description of Jansonia jurassica indicated the presence of a hollow apical horn. Re-examination of the type material by Jansonius (1986) failed to identify this feature. As neither the type nor Australian specimens have apical horns, this feature is not considered diagnostic of the species, nor the genus.
The distinct leathery brown appearance of the cyst, regardless of thermalmaturity, is considered a primary diagnostic feature. The colour of the cyst wall is rarely uniform across a single specimen. The jagged nature of the archeopyle margin is indicative of anterior intercalary plates, but these have yet to be directly observed. The presence of three to five anterior intercalary plates is likely given the overall similarities between Jansonia and Microdinium Cookson and Eisenack, 1960a. While both Jansonia and Mikrocysta Bjaerke, 1980 are small cysts with characteristic cingular constrictions, wider hypocysts and tAtI archeopyles, Jansonia is distinct in having six cingular plates, while Mikrocysta has seven (Below, 1987). Low relief surface ornament, comprised of discrete grana and muri, typically unobservable using TLM, was observed using SEM imaging. This ornament style, particularly the presence of discrete muri, has been previously documented in Jansonia manifesta Riding and Walton in Riding et al., 1991 and appears to be characteristic of the genus.
Jansonia jurassica Pocock, 1972, p.97–98, pl.29, figs.8–9; text-figs.14–15. Holotype: Pocock, 1972, pl.29, fig.8; Jansonius, 1986, pl.3, figs.4–6. Age: late Bajocian.
---------------------------------------------------------------------------------------------------
Locus typicus: Tidewater Eastern Crown, W Canada
Stratum typicum: Late Bajocian
Original description: Pocock, 1972, p.97
Vesicle small; more or less isodiametric; pear-shaped in outline; epitheca terminated by a smoothly rounded hollow apical horn about 10.0 Ám long which is only very rarely preserved (seen on only one of over two hundred specimens examined); hypotheca hemispherical; smooth; no antapical processes developed; transverse furrow about 6.0 µm wide; parallel-sided; slightly helicoidal; longitudinal furrow rarely seen; sutures reflected onto surface of vesicle of some specimens as very faint lines of minute granules; invisible on others; tabulation impossible to determine from any one specimen; partial tabulation, determined from several grains, appears to be (?'), 6'', 6g, 6''', 1P, 1''''; archeopyle apical with simple free operculum; vesicle two-layered; capsule less than 0.25 µm thick; smooth; tightly appressed to outer layer; outer layer 0.5-1.0 µm thick; surface finely and closely granulose; colour brown; length 25.0 (33.0) 40.0 µm (excluding apical horn); width 23.0 (33.0) 43.0 µm.
Supplemental description: Jansonius, 1986, p.211
(Holotype) 37 x 37 µm, dorsal side up (4" in the center); characteristically brown and leathery in appearance, wall thinning and becoming nearly colorless along the apical archeopyle; often darker in the region of the cingulum. The cingulum (6-8 µm wide) is distinctly delineated by two ridges; the displacement of the cingulum on the ventral side is very slight. Precingular plates are indicated by small acccessory sutures; however, it is difficult to discern their number (apparently six). No more than a few vague ridges delineating postcingulars can be observed. The whole surface of the grain is covered with a sculpture of low, often interrupted, wandering ridges that form a shallow incomplete reticulum; muri, and grooves (or brochi) between them, about 0.4-0.5 µm wide; wall, including sculpture, about 0.8-0.9 µm thick (thinner near apex). At low power the sculpture appears as granulation, possibly because the muri are uneven in height and bulk. (In other specimens the sculpture actually may be reduced to scattered granules.) It is characteristic of the preservation that many random cracks occur in the cyst, especially in the hypocyst, which do not seem to coincide with any paratabulation.
Remarks. Some hundred specimens have been seen by me, and a few appear to have a small thin apical operculum attached to one of the precingulars. No specimens have been observed showing the apical horn mentioned by Pocock. The one specimen from which it was described is lost, and was not photographed; thus it seems possible that abnormal development, or extraneous matter, may have been responsible for this appearance. The absence of paratabulation (other than incipient accessory precingular sutures and the distinct cingulum) is characteristic.
---------------------------------------------------------------------------------------------------
Emended description Vitacca et al., 2022:
(Plate XI, 1–6; Plate XII, 1)
1972 Jansonia jurassica Pocock, p. 97–98
Holotype: Pocock, 1972, p. 97, pl. 29, 8., Jansonius, 1986, pl. 3, 4–6.
Diagnosis: A pear-shaped species of Jansonia with a short, narrow epicyst and a larger, well-rounded hypocyst. Autophragm granulate, verrucate or rugulate. Low-relief crests indicate gonyaulacalean tabulation and combination archeopyle; operculum free.
Description: A small, sub-ovoidal to pear-shaped dinoflagellate cyst that is characteristically brown to dark brown, generally darkest around the cingulum, and lightest in colour apically. Epicyst shorter and narrower than hypocyst, which is antapically rounded. The cyst lacks any horns or protuberances. Autophragm thick, granulate or faintly verrucate and rugulate. Ornamental elements often fused to form sutural ridges, usually more pronounced antapically. The cingulum is generally well defined, weakly laevorotatory, ps prominent, widening antapically. Hypocystal tears are common. Inferred tabulation formula:? pr,?4′,?3–5a,?6–7″, 6c, 6″’, 1p, 1″”,?5–6s (Fig. 11A, A`). Archeopyle combination apical and anterior intercalary, type (tAtI), operculum free, the margin is often jagged or torn.
Dimensions: (23 specimens measured)
Length: 18 (23) 31
Width: 16 (21) 26
Remarks: The original description of Jansonia jurassica indicated the presence of a hollow apical horn. Re-examination of the type material by Jansonius (1986) failed to identify this feature. As neither the type nor Australian specimens have apical horns, this feature is not considered diagnostic of the species, nor the genus.
The distinct leathery brown appearance of the cyst, regardless of thermalmaturity, is considered a primary diagnostic feature. The colour of the cyst wall is rarely uniform across a single specimen. The jagged nature of the archeopyle margin is indicative of anterior intercalary plates, but these have yet to be directly observed. The presence of three to five anterior intercalary plates is likely given the overall similarities between Jansonia and Microdinium Cookson and Eisenack, 1960a. While both Jansonia and Mikrocysta Bjaerke, 1980 are small cysts with characteristic cingular constrictions, wider hypocysts and tAtI archeopyles, Jansonia is distinct in having six cingular plates, while Mikrocysta has seven (Below, 1987). Low relief surface ornament, comprised of discrete grana and muri, typically unobservable using TLM, was observed using SEM imaging. This ornament style, particularly the presence of discrete muri, has been previously documented in Jansonia manifesta Riding and Walton in Riding et al., 1991 and appears to be characteristic of the genus.