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Vexillocysta
From Williams et al., 2017:
[Vexillocysta, Harding, 1990b, p. 45; ex Harding in Williams et al., 1998, p. 628.
This name was not validly published in Harding (1990b) since the name of the "type species" was not validly published.
Type species: Vexillocysta retis, Harding, 1990 (pl.24, fig.8)]
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Original description: [Harding, 1990]:
Diagnosis:
Shape: Ambitus subcircular to prolate ovoidal, modified by numerous processes. Epicyst and hypocyst of about equal dimensions. Greatest width in equatorial region. Moderate dorso-ventral compression.
Phragma: Endophragm ca. 0.75 µm thick, seemingly almost laevigate where visible (Plate 24, Fig. 13). Periphragm 0.3-0.5 µm thick, consists of a base layer overlain by interconnected sporopollenin fibrils forming a pseudo-reticulum (max. Iumina diameter 1 µm). Many of the fibrils terminate perpendicular to the plane of the periphragm, giving a globular appearance to the reticulum. The numerous, flat, blade-like processes (intra- and peni-tabular) are proximally hollow, distally solid and often bifurcate. The processes are faintly striate in appearance. Process width (1-3.5 µm) is inversely proportional to length (6-12 µm), both long and short processes may be found on one specimen (shorter processes in mid-dorsal and mid-ventral areas). Both cyst wall layers are closely adpressed except for the process bases.
Paratabulation: The complex distribution of the processes makes the determination of the paratabulation difficult, but it appears to be compatible with a gonyaulacoid type. Apical paratabulation determined from archaeopyle sutures: 4`, 6" + ai.
Archaeopyle: Type (4A), free, simple polyplacoid operculum. Short accessory archaeopyle sutures formed between precingular paraplates.
Paracingulum: Occasionally recognisable due to alignment of process blades delineating a process-free band.
Parasulcus: Difficult to detect save for on excysted specimens where ai can be distinguished along the archaeopyle margin.
Dimensions:
Length = (60) 51 (40) µm. Width = (50) 44 (35) µm. Specimens = 25 (20).
Affinities:
The genus Vexillocysta differs from Epiplosphaera Klement 1960 (which also has an apical archaeopyle), in the nature of the processes developed on the external cyst surface. In the new genus the processes may, in some instances, be aligned with adjacent ones. However, in Epiplosphaera, the processes arise from a complex reticular network of septa. Of the specimens of Cleistosphaeridium described by McIntyre & Brideaux (1980) from Canada, the morphotype referred to as C. sp. KE bears a strong resemblance to Vexillocysta retis, although it should be noted that the Canadian material is of Valanginian age.
This form is a common constituent of the floras studied - especially in the Hauptblatterton facies. Later Barremian forms have a more subdued reticulation and fewer, more slender processes.
[Vexillocysta, Harding, 1990b, p. 45; ex Harding in Williams et al., 1998, p. 628.
This name was not validly published in Harding (1990b) since the name of the "type species" was not validly published.
Type species: Vexillocysta retis, Harding, 1990 (pl.24, fig.8)]
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Harding, 1990]:
Diagnosis:
Shape: Ambitus subcircular to prolate ovoidal, modified by numerous processes. Epicyst and hypocyst of about equal dimensions. Greatest width in equatorial region. Moderate dorso-ventral compression.
Phragma: Endophragm ca. 0.75 µm thick, seemingly almost laevigate where visible (Plate 24, Fig. 13). Periphragm 0.3-0.5 µm thick, consists of a base layer overlain by interconnected sporopollenin fibrils forming a pseudo-reticulum (max. Iumina diameter 1 µm). Many of the fibrils terminate perpendicular to the plane of the periphragm, giving a globular appearance to the reticulum. The numerous, flat, blade-like processes (intra- and peni-tabular) are proximally hollow, distally solid and often bifurcate. The processes are faintly striate in appearance. Process width (1-3.5 µm) is inversely proportional to length (6-12 µm), both long and short processes may be found on one specimen (shorter processes in mid-dorsal and mid-ventral areas). Both cyst wall layers are closely adpressed except for the process bases.
Paratabulation: The complex distribution of the processes makes the determination of the paratabulation difficult, but it appears to be compatible with a gonyaulacoid type. Apical paratabulation determined from archaeopyle sutures: 4`, 6" + ai.
Archaeopyle: Type (4A), free, simple polyplacoid operculum. Short accessory archaeopyle sutures formed between precingular paraplates.
Paracingulum: Occasionally recognisable due to alignment of process blades delineating a process-free band.
Parasulcus: Difficult to detect save for on excysted specimens where ai can be distinguished along the archaeopyle margin.
Dimensions:
Length = (60) 51 (40) µm. Width = (50) 44 (35) µm. Specimens = 25 (20).
Affinities:
The genus Vexillocysta differs from Epiplosphaera Klement 1960 (which also has an apical archaeopyle), in the nature of the processes developed on the external cyst surface. In the new genus the processes may, in some instances, be aligned with adjacent ones. However, in Epiplosphaera, the processes arise from a complex reticular network of septa. Of the specimens of Cleistosphaeridium described by McIntyre & Brideaux (1980) from Canada, the morphotype referred to as C. sp. KE bears a strong resemblance to Vexillocysta retis, although it should be noted that the Canadian material is of Valanginian age.
This form is a common constituent of the floras studied - especially in the Hauptblatterton facies. Later Barremian forms have a more subdued reticulation and fewer, more slender processes.