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Tetrachacysta spinosigibberosa
From Fensome et al., 2019:
Tetrachacysta spinosigibberosa (Brideaux and Fisher, 1976, p.22–24, pl.4, fig.9; pl.5, figs.1–16) Backhouse, 1988, p.110.
Holotype: Brideaux and Fisher, 1976, pl.5, figs.1,5–8.
Originally Horologinella, subsequently (and now) Tetrachacysta.
Age: late Oxfordian–?Portlandian.
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Original diagnosis: Brideaux and Fisher, 1976, p. 22: Horologinella spinosigibberosa
Autoblast longer than broad; hourglassshaped; dorso-ventrally compressed. Autophragm bearing apiculate to vermiculate sculpture in more or less continuous bands, or in clusters interpreted as representing reflected plates. Archeopyle apical, formed by the loss of ?four reflected apical plates; operculum simple. Reflected tabulation scheme proposed as ?4", 5"-?6", 0c, 5""", ?0"""". Medial, transverse, and medial longitudinal areas lacking processes and interpreted as a reflected cingulum and sulcus, respectively.
Original description: Brideaux and Fisher, 1976, p. 22-23: Horologinella spinosigibberosa
The autoblast is longer than broad, dorso-ventrally compressed, and has an outline that is slightly to markedly hourglass-shaped. The maximum width of the autoblast occurs at the apices and the minimum width occurs at the latitude of the reflected cingulum. The apex is either nearly flat or medially slightly invaginated. The antapex is broadly rounded, to nearly flat in outline. An occasional specimen may show a slightly invaginated antapical outline similar to the apex. There are no apical or antapical horns or prominences. The wall of the cyst cannot be differentiated into a periphragm and endophragm layer and is termed an autophragm. The thickness of the autophragm in optical section is about 1.0 µm. The surface of the autophragm bears solid, variably shaped, vermiculate to apiculate sculptural elements. The apiculate processes are 0.5 to 1.0 µm high, and are conical, baculate or occasionally pilate. A mixture of these process types may occur on any given specimen. The vermiculate processes are sinuous, arcuate or irregular in course, occasionally anastomosing in an irregular meshwork, and are low, 0.5 to 1.0 µm in height, and narrow, from 0.25 to 0.5 µm in width. The distribution of these processes is discussed in connection with reflected tabulation patterns and the presence of what is interpreted as a cingulum and sulcus.
An apical opening is present on many specimens and is interpreted as an apical archeopyle, as evidenced by its angular outline. The archeopyle is located symmetrically with respect to a vertical median line. The operculum is simple and bears vermiculate to apiculate sculpture; although there is no indication of tabulation, analysis of the archeopyle outline suggests that the operculum is formed of four apical reflected plates. The operculum is attached or free; isolated opercula have been observed. The structure and sculpture of the autoblast offer evidence for the proposed reflected tabulation scheme: ?4", 5"-?6", 0c, 5""", ?0"""". Dorsal epitractal processes are generally present as a continuous band. However, the angular edge of the archeopyle opening and the two ventral epitractal sculpture clusters, separated by the medial longitudinal process-free region, suggest that at least five, and possibly six reflected precingular plates are represented. On some specimens, an occasional accessory archeopyle suture running from the archeopyle opening, and the rare presence of a low irregular ridge dividing the dorsal process band, lend further support to this interpretation. Similarly, two ventral hypotractal process clusters and a dorsal hypotractal band of processes suggest that at least five reflected post-cingular plates may be represented. The antapex is free of processes; therefore, interpretation of reflected antapical tabulation is not possible. A medial process-free region running transversely about the autoblast, and including the zone of minimum width, is interpreted as a reflected cingular region. This process-free band is quite broad, from 16 to 18 µm wide dorsally but narrowing to 8 to 10 µm wide ventrally. The narrowest part of this cingular area occurs ventrally to the left side of a vertical median line. The cingular region thus appears slightly laevo-rotary. A similar longitudinal process-free area is interpreted as a reflected sulcal region. The sulcus runs from directly below that portion of the archeopyle adjacent to the median-line to the antapex, where it broadens to include the whole of the ventral antapical area, and where it is terminated at the periphery of the dorsal hypotractal process band. The width of the sulcus at the latitude of the two ventral process clusters is 4 to 8 µm. The features described above are shown with varying clarity on available specimens. The archeopyle commonly is present, but often poorly exhibited. The dorsal process bands and ventral process clusters are not always clearly developed. The reflected tabulation scheme proposed above is necessarily the result of an analysis of features on many specimens.
Dimensions - Autoblast length, 30-55 µm; maximum autoblast width, 37-40 µm - minimum autoblast width, 20-35 µm.
Tetrachacysta spinosigibberosa (Brideaux and Fisher, 1976, p.22–24, pl.4, fig.9; pl.5, figs.1–16) Backhouse, 1988, p.110.
Holotype: Brideaux and Fisher, 1976, pl.5, figs.1,5–8.
Originally Horologinella, subsequently (and now) Tetrachacysta.
Age: late Oxfordian–?Portlandian.
---------------------------------------------------------------------------------------------------
Original diagnosis: Brideaux and Fisher, 1976, p. 22: Horologinella spinosigibberosa
Autoblast longer than broad; hourglassshaped; dorso-ventrally compressed. Autophragm bearing apiculate to vermiculate sculpture in more or less continuous bands, or in clusters interpreted as representing reflected plates. Archeopyle apical, formed by the loss of ?four reflected apical plates; operculum simple. Reflected tabulation scheme proposed as ?4", 5"-?6", 0c, 5""", ?0"""". Medial, transverse, and medial longitudinal areas lacking processes and interpreted as a reflected cingulum and sulcus, respectively.
Original description: Brideaux and Fisher, 1976, p. 22-23: Horologinella spinosigibberosa
The autoblast is longer than broad, dorso-ventrally compressed, and has an outline that is slightly to markedly hourglass-shaped. The maximum width of the autoblast occurs at the apices and the minimum width occurs at the latitude of the reflected cingulum. The apex is either nearly flat or medially slightly invaginated. The antapex is broadly rounded, to nearly flat in outline. An occasional specimen may show a slightly invaginated antapical outline similar to the apex. There are no apical or antapical horns or prominences. The wall of the cyst cannot be differentiated into a periphragm and endophragm layer and is termed an autophragm. The thickness of the autophragm in optical section is about 1.0 µm. The surface of the autophragm bears solid, variably shaped, vermiculate to apiculate sculptural elements. The apiculate processes are 0.5 to 1.0 µm high, and are conical, baculate or occasionally pilate. A mixture of these process types may occur on any given specimen. The vermiculate processes are sinuous, arcuate or irregular in course, occasionally anastomosing in an irregular meshwork, and are low, 0.5 to 1.0 µm in height, and narrow, from 0.25 to 0.5 µm in width. The distribution of these processes is discussed in connection with reflected tabulation patterns and the presence of what is interpreted as a cingulum and sulcus.
An apical opening is present on many specimens and is interpreted as an apical archeopyle, as evidenced by its angular outline. The archeopyle is located symmetrically with respect to a vertical median line. The operculum is simple and bears vermiculate to apiculate sculpture; although there is no indication of tabulation, analysis of the archeopyle outline suggests that the operculum is formed of four apical reflected plates. The operculum is attached or free; isolated opercula have been observed. The structure and sculpture of the autoblast offer evidence for the proposed reflected tabulation scheme: ?4", 5"-?6", 0c, 5""", ?0"""". Dorsal epitractal processes are generally present as a continuous band. However, the angular edge of the archeopyle opening and the two ventral epitractal sculpture clusters, separated by the medial longitudinal process-free region, suggest that at least five, and possibly six reflected precingular plates are represented. On some specimens, an occasional accessory archeopyle suture running from the archeopyle opening, and the rare presence of a low irregular ridge dividing the dorsal process band, lend further support to this interpretation. Similarly, two ventral hypotractal process clusters and a dorsal hypotractal band of processes suggest that at least five reflected post-cingular plates may be represented. The antapex is free of processes; therefore, interpretation of reflected antapical tabulation is not possible. A medial process-free region running transversely about the autoblast, and including the zone of minimum width, is interpreted as a reflected cingular region. This process-free band is quite broad, from 16 to 18 µm wide dorsally but narrowing to 8 to 10 µm wide ventrally. The narrowest part of this cingular area occurs ventrally to the left side of a vertical median line. The cingular region thus appears slightly laevo-rotary. A similar longitudinal process-free area is interpreted as a reflected sulcal region. The sulcus runs from directly below that portion of the archeopyle adjacent to the median-line to the antapex, where it broadens to include the whole of the ventral antapical area, and where it is terminated at the periphery of the dorsal hypotractal process band. The width of the sulcus at the latitude of the two ventral process clusters is 4 to 8 µm. The features described above are shown with varying clarity on available specimens. The archeopyle commonly is present, but often poorly exhibited. The dorsal process bands and ventral process clusters are not always clearly developed. The reflected tabulation scheme proposed above is necessarily the result of an analysis of features on many specimens.
Dimensions - Autoblast length, 30-55 µm; maximum autoblast width, 37-40 µm - minimum autoblast width, 20-35 µm.