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Athigmatocysta glabra
Athigmatocysta glabra, Duxbury, 1977
Originally (and now) Athigmatocysta, subsequently Endoscrinium, thirdly Scriniodinium. Below, 1981 transferred this species to Endoscrinium (Klement, 1960) Vozzhennikova, 1967. Jan du Chêne et al., 1986, transferred the species to Scriniodinium Klement, 1957. Harding, 1990b, retained it in Athigmatocysta.
Holotype: Duxbury, 1977, pl.11, figs.1,6; Jan du Chêne et al., 1986, pl.111, figs.9-10
Locus typicus: Speeton Clay, Speeton, England.
Stratum typicum: Berriasian-Barremian
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Original description: [Duxbury, 1977, p. 24]:
Diagnosis:
A thin-walled, distinctly bi-layered proximo-cavate cyst.
The tabulation ?4", 6", 6c, 6""", 1p, 1pv, 1"""" is outlined on the periphragm by distinctly denticulate sutural crests of variable height. The endophragm is ellipsoidal, slightly longer than broad and produced into a low apical prominence which reflects the short apical horn borne by the periphragm. Both periphragm and endophragm are smooth.
Archeopyle precingular, formed by loss of plate 3".
Dimensions:
Holotype 94x79 µm. Range 94(83)69x71(70)61 µm.
Remark:
This is a thin-walled form and is usually distorted. In better preserved specimens, there is apparently complete cavation between the endophragm and periphragm. Obviously there must be some connection between the body layers in order to maintain the position of the endoblast within the periblast. Unfortunately, no such connection was apparent here. The endophragm commonly exhibits an archeopyle reflecting that in the periphragm formed by loss of plate 3". It is much less angular than 3".
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Harding, 1990, p.28:
Remarks:
This rare species is not encountered in samples younger than early Barremian in age. The phragma are thin (periphragm-0.75 µm, endophragm <0.5 µm) and prone to crushing. S-type sexiform gonyaulacoid paratabulation of: 2pr, 4", 6", 6c, 6""", 1"""", 1p, 5s, indicated by parasutural ridges. These ridges are semicircular in section ca. 1 µm in height and width and distally "nodular". This latter feature may have been interpreted by Duxbury (1977) as denticulations of the parasutural ridges. lu is long and sickle-shaped with a very small A, approximating Q in size. This morphotype displays a Jurassica-pattern paratabulation, with symmetrical antapical, Q/B apical and lu/li ventral arrangements (Helenes 1986). Some specimens however, do show a loss of the A/li contact (Plate 10, Fig. 5) as in Gonyaulacysta fastigiata (Helenes 1986: 80).
Originally (and now) Athigmatocysta, subsequently Endoscrinium, thirdly Scriniodinium. Below, 1981 transferred this species to Endoscrinium (Klement, 1960) Vozzhennikova, 1967. Jan du Chêne et al., 1986, transferred the species to Scriniodinium Klement, 1957. Harding, 1990b, retained it in Athigmatocysta.
Holotype: Duxbury, 1977, pl.11, figs.1,6; Jan du Chêne et al., 1986, pl.111, figs.9-10
Locus typicus: Speeton Clay, Speeton, England.
Stratum typicum: Berriasian-Barremian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Duxbury, 1977, p. 24]:
Diagnosis:
A thin-walled, distinctly bi-layered proximo-cavate cyst.
The tabulation ?4", 6", 6c, 6""", 1p, 1pv, 1"""" is outlined on the periphragm by distinctly denticulate sutural crests of variable height. The endophragm is ellipsoidal, slightly longer than broad and produced into a low apical prominence which reflects the short apical horn borne by the periphragm. Both periphragm and endophragm are smooth.
Archeopyle precingular, formed by loss of plate 3".
Dimensions:
Holotype 94x79 µm. Range 94(83)69x71(70)61 µm.
Remark:
This is a thin-walled form and is usually distorted. In better preserved specimens, there is apparently complete cavation between the endophragm and periphragm. Obviously there must be some connection between the body layers in order to maintain the position of the endoblast within the periblast. Unfortunately, no such connection was apparent here. The endophragm commonly exhibits an archeopyle reflecting that in the periphragm formed by loss of plate 3". It is much less angular than 3".
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Harding, 1990, p.28:
Remarks:
This rare species is not encountered in samples younger than early Barremian in age. The phragma are thin (periphragm-0.75 µm, endophragm <0.5 µm) and prone to crushing. S-type sexiform gonyaulacoid paratabulation of: 2pr, 4", 6", 6c, 6""", 1"""", 1p, 5s, indicated by parasutural ridges. These ridges are semicircular in section ca. 1 µm in height and width and distally "nodular". This latter feature may have been interpreted by Duxbury (1977) as denticulations of the parasutural ridges. lu is long and sickle-shaped with a very small A, approximating Q in size. This morphotype displays a Jurassica-pattern paratabulation, with symmetrical antapical, Q/B apical and lu/li ventral arrangements (Helenes 1986). Some specimens however, do show a loss of the A/li contact (Plate 10, Fig. 5) as in Gonyaulacysta fastigiata (Helenes 1986: 80).