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Hebecysta balmei
Hebecysta balmei (Stover and Helby, 1987a, p.109–110, figs.7A–H) Below, 1987a, p.126. Emendation: Below, 1987a, p.126, as Hebecysta balmei.
Originally Heibergella, subsequently (and now) Hebecysta.
Holotype: Stover and Helby, 1987a, figs.7A–B; Fensome et al., 1996, figs.1–2 — p.2061.
Paratypes: Stover and Helby, 1987
Locus typicus: Ashmore Reef-1 Well, 3573 m, Bonaparte Basin, Australia
Stratum typicum: Norian
Translation Below, 1987: Secretary of State, Canada, Translation Bureau, p. 319-320
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G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hebecysta balmei (Stover and Helby, 1987a) Below, 1987a, emend. Below, 1987a. This species was emended by Below (1987a) as follows, Tabulation cop, pop, cap, 5', 3a, 7", nc, n”’, n”“, ns. Cyst proximate, ovoidal, ovaloidal, biconical, sometimes slightly compressed dorsoventrally, apex rounded, antapex rounded, acavate to epicavate. Surface finely to coarsely rugulate. Cingulum laevorotatory, with anterior and posterior margins marked preferentially by rugulae. Sulcus broad. Archeopyle anterior intercalary, 1a + 2a + 3a. Operculum monoareate, secate 2a, very seldom bi- or triareate. According to Stover and Helby (1987a), this species differs from other species of Hebecysta in being reticulate. The autophragm has low smooth ridges forming a relatively large mesh reticulum. Lumina polygonal, more or less equidimensional to elongate and 2-10 µm in diameter. Lumina more elongate near poles. Archeopyle intercalary and apparently formed from loss of more than one paraplate. Paracingulum delineated by two continuous parallel transverse ridges. Size: 43-68 µm long. 38-61 µm wide.
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Original description: Stover and Helby, 1987, p. 109-110: Heibergella balmei
Cysts proximate, subspherical to ovate; when ovate apex more narrowly rounded than antapex. Autophragm thin, generally less than 1 Ám, and ornamented with low, more or less continuous, smooth ridges forming a relatively large mesh reticulum. Height and width of the muri essentially the same (generally 1 Ám or less over most of the cyst, and may be up to about 2 Ám at the poles); lumina polygonal, more or less equidimensional to elongate and from 2-10 Ám in maximum diameter. More elongate lumina near poles with longer sides aligned longitudinally, or nearly so. Archeopyle intercalary and apparently formed by loss of one or more paraplates. Paracingulum with 2 continuous, parallel transverse ridges marginal to it. Ends of paracingulum moderately offset. Parasulcus not indicated or may be delimited by a continuous, loop-like, posteriorly closed ridge mainly on the hypocyst and extending a few Ám onto the epicyst. Specimens 43(58)68 Ám in length, and 38(51)61 Ám in width; 20 specimens measured.
Comment: The exact shape of the archeopyle has not been determined owing to compression, folding and tearing of the autophragm; however, the size of the opening on most specimens suggests that 2 or more paraplates are involved in archeopyle formation. Because the posterior archeopyle margin is within a few microns of the paracingulum, the narrow precingular band between archeopyle and paracingulum may be obscured by folding. On such specimens, the archeopyle may appear to be precingular. Reticulation varies not only among specimens but also on parts of individuals. Rare specimens appear almost smooth but are identified by the distinctive crenulation of the apexes. Muri may be slightly higher and lumina somewhat larger in the polar areas than on other parts of the cyst. Similarly, on some specimens, reticulation is evident on all of the cyst, whereas on others it is faintly developed adjacent to the paracingulum.
Emended description: Below, 1987, p. 126
Arrangement of vesicles/plates on the dinoflagellate amphiesma cop, pop, cap, 5', 3a, 7'', nc, n''', n'''', ns. Cystic habit proximate, ovoidal, ovaloidal, biconical, sometimes slightly compressed dorsoventrally, apexrounded, antapex rounded but also flattened or weakly indented, acavate or epicavate, equatorial cross section circular to oval; size small; wall composed of thin pedium and firm luxuria; surface finely to coarsely rugulate; areation rudimentary, NR PR/XPR, NR'/5', NRa/3a, NR''/7'', NRc, NR''', NR'''', NRs/Xs; cingulum equatorial, helicoid laevorotatory, slightly indented with the anterior and posterior margin marked preferentially by rugulae; sulcus broad, weakly indented, differentiated from adsulcal region; archaeopyle anterior intercalary, 1a +2a + 3a; operculum monoareate, secate, 2as, very seldom bi- or triareate, general opercular formula 1as + 2as + 3as.
Remarks: The pattern of the crude rugulae on the surface of the cyst is random and variable. They are not oriented along fines. Only the cingular margins are traced by often firmer rugulae perpendicular to the polar axis. Usually the archaeopyle and operculum provide the only indications of a potential thecal tabulation. The exit hole is formed by the large anterior intercalary area 2a in an exactly mediodorsal location. As a rule, 2a is symmetrical, heptagonal, and bounded posteriorly by 3'', 4'', and 5'' (Plate 12, Fig. 1, 12, 17, and 18). Among other stratigraphically early taxa of the subfamily Rhaetogonyaulacoideae, this form is so far known only as a variant. The geometry of 2a typical only of the Sinemurian Liasidium variabile Drugg 1978 and taxa of the genus Moesiodinium from the Malm-Lower Cretaceous. However, there were also very few specimens in these assemblages with a posteriorly geniculate operculum, i.e., one having posterior contact with only two precingulars. Precisely this variation of the shape of 2a is known also in many other taxa of the tribe Phallocysteae. The archaeopyle margins and archaeopyle sutures give the following indications regarding the configuration formed by the opercular area with neighbouring areae not reflected by fines (Figure 67): Dextrally and sinistrally, the archaeopyle is adjoined by other large anterior intercalaries. Posteriorly it is bounded by the planate area 4'', which in turn is bounded sinistrally by a camerate 3'' and dextrally by a camerate 5''. Since these three area, like the dorsal precingulars of Rhaetogonyaulax, are very low, the archaeopyle reaches close to the cingulum. Certain specimens, particularly those with fine rugulae, partially reveal area boundaries (Plate 12, Fig 5). A list of the observed area shapes is compiled in Figure 67. Growth, or even overlapping of thecal plates is not reflected. The emendation is based on the description of the epicystal areation.
Affinities:
Stover and Helby, 1987, p. 110: Heibergella balmei
Heibergella balmei differs from other species of Heibergella described by Bujak and Fisher (1976) in being reticulate: H. asymmetrica is smooth to scabrate, H. salebrosacea is densely granular and H. aculeata is spinate. Heibergella? kendelbachia is smooth to granulate and has a distinctive rhomboidal shape. A cavate form closely resembling H. balmei, has been recorded in the H. balmei Zone.
Originally Heibergella, subsequently (and now) Hebecysta.
Holotype: Stover and Helby, 1987a, figs.7A–B; Fensome et al., 1996, figs.1–2 — p.2061.
Paratypes: Stover and Helby, 1987
Locus typicus: Ashmore Reef-1 Well, 3573 m, Bonaparte Basin, Australia
Stratum typicum: Norian
Translation Below, 1987: Secretary of State, Canada, Translation Bureau, p. 319-320
--------------------------------------------------
G.L. Williams short notes on species, Mesozoic-Cenozoic dinocyst course, Urbino, Italy, May 17-22, 1999 - LPP VIEWER CD-ROM 99.5.
Hebecysta balmei (Stover and Helby, 1987a) Below, 1987a, emend. Below, 1987a. This species was emended by Below (1987a) as follows, Tabulation cop, pop, cap, 5', 3a, 7", nc, n”’, n”“, ns. Cyst proximate, ovoidal, ovaloidal, biconical, sometimes slightly compressed dorsoventrally, apex rounded, antapex rounded, acavate to epicavate. Surface finely to coarsely rugulate. Cingulum laevorotatory, with anterior and posterior margins marked preferentially by rugulae. Sulcus broad. Archeopyle anterior intercalary, 1a + 2a + 3a. Operculum monoareate, secate 2a, very seldom bi- or triareate. According to Stover and Helby (1987a), this species differs from other species of Hebecysta in being reticulate. The autophragm has low smooth ridges forming a relatively large mesh reticulum. Lumina polygonal, more or less equidimensional to elongate and 2-10 µm in diameter. Lumina more elongate near poles. Archeopyle intercalary and apparently formed from loss of more than one paraplate. Paracingulum delineated by two continuous parallel transverse ridges. Size: 43-68 µm long. 38-61 µm wide.
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Original description: Stover and Helby, 1987, p. 109-110: Heibergella balmei
Cysts proximate, subspherical to ovate; when ovate apex more narrowly rounded than antapex. Autophragm thin, generally less than 1 Ám, and ornamented with low, more or less continuous, smooth ridges forming a relatively large mesh reticulum. Height and width of the muri essentially the same (generally 1 Ám or less over most of the cyst, and may be up to about 2 Ám at the poles); lumina polygonal, more or less equidimensional to elongate and from 2-10 Ám in maximum diameter. More elongate lumina near poles with longer sides aligned longitudinally, or nearly so. Archeopyle intercalary and apparently formed by loss of one or more paraplates. Paracingulum with 2 continuous, parallel transverse ridges marginal to it. Ends of paracingulum moderately offset. Parasulcus not indicated or may be delimited by a continuous, loop-like, posteriorly closed ridge mainly on the hypocyst and extending a few Ám onto the epicyst. Specimens 43(58)68 Ám in length, and 38(51)61 Ám in width; 20 specimens measured.
Comment: The exact shape of the archeopyle has not been determined owing to compression, folding and tearing of the autophragm; however, the size of the opening on most specimens suggests that 2 or more paraplates are involved in archeopyle formation. Because the posterior archeopyle margin is within a few microns of the paracingulum, the narrow precingular band between archeopyle and paracingulum may be obscured by folding. On such specimens, the archeopyle may appear to be precingular. Reticulation varies not only among specimens but also on parts of individuals. Rare specimens appear almost smooth but are identified by the distinctive crenulation of the apexes. Muri may be slightly higher and lumina somewhat larger in the polar areas than on other parts of the cyst. Similarly, on some specimens, reticulation is evident on all of the cyst, whereas on others it is faintly developed adjacent to the paracingulum.
Emended description: Below, 1987, p. 126
Arrangement of vesicles/plates on the dinoflagellate amphiesma cop, pop, cap, 5', 3a, 7'', nc, n''', n'''', ns. Cystic habit proximate, ovoidal, ovaloidal, biconical, sometimes slightly compressed dorsoventrally, apexrounded, antapex rounded but also flattened or weakly indented, acavate or epicavate, equatorial cross section circular to oval; size small; wall composed of thin pedium and firm luxuria; surface finely to coarsely rugulate; areation rudimentary, NR PR/XPR, NR'/5', NRa/3a, NR''/7'', NRc, NR''', NR'''', NRs/Xs; cingulum equatorial, helicoid laevorotatory, slightly indented with the anterior and posterior margin marked preferentially by rugulae; sulcus broad, weakly indented, differentiated from adsulcal region; archaeopyle anterior intercalary, 1a +2a + 3a; operculum monoareate, secate, 2as, very seldom bi- or triareate, general opercular formula 1as + 2as + 3as.
Remarks: The pattern of the crude rugulae on the surface of the cyst is random and variable. They are not oriented along fines. Only the cingular margins are traced by often firmer rugulae perpendicular to the polar axis. Usually the archaeopyle and operculum provide the only indications of a potential thecal tabulation. The exit hole is formed by the large anterior intercalary area 2a in an exactly mediodorsal location. As a rule, 2a is symmetrical, heptagonal, and bounded posteriorly by 3'', 4'', and 5'' (Plate 12, Fig. 1, 12, 17, and 18). Among other stratigraphically early taxa of the subfamily Rhaetogonyaulacoideae, this form is so far known only as a variant. The geometry of 2a typical only of the Sinemurian Liasidium variabile Drugg 1978 and taxa of the genus Moesiodinium from the Malm-Lower Cretaceous. However, there were also very few specimens in these assemblages with a posteriorly geniculate operculum, i.e., one having posterior contact with only two precingulars. Precisely this variation of the shape of 2a is known also in many other taxa of the tribe Phallocysteae. The archaeopyle margins and archaeopyle sutures give the following indications regarding the configuration formed by the opercular area with neighbouring areae not reflected by fines (Figure 67): Dextrally and sinistrally, the archaeopyle is adjoined by other large anterior intercalaries. Posteriorly it is bounded by the planate area 4'', which in turn is bounded sinistrally by a camerate 3'' and dextrally by a camerate 5''. Since these three area, like the dorsal precingulars of Rhaetogonyaulax, are very low, the archaeopyle reaches close to the cingulum. Certain specimens, particularly those with fine rugulae, partially reveal area boundaries (Plate 12, Fig 5). A list of the observed area shapes is compiled in Figure 67. Growth, or even overlapping of thecal plates is not reflected. The emendation is based on the description of the epicystal areation.
Affinities:
Stover and Helby, 1987, p. 110: Heibergella balmei
Heibergella balmei differs from other species of Heibergella described by Bujak and Fisher (1976) in being reticulate: H. asymmetrica is smooth to scabrate, H. salebrosacea is densely granular and H. aculeata is spinate. Heibergella? kendelbachia is smooth to granulate and has a distinctive rhomboidal shape. A cavate form closely resembling H. balmei, has been recorded in the H. balmei Zone.