Back
Aidelocysta clavata
Aidelocysta *clavata, Riding, Helby and Stevens in Riding and Helby, 2001g, p. 179,181, figs.1A-P.
Holotype: Riding and Helby, 2001g, figs.1I-L.
Type locaility: conventional core sample in Wanaea-2 well at 2880.50m.
Stratigraphical distribution: ranges from the Tithonian upper dingodinium jurassicum Zone (5aii) tot the Berriasian Kalyptea wisemaniae Zone (4biii)
Age: Tithonian-Berriasian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description [Riding & Helby, 2001g]:
Description:
A species of Aidelocysta which may be acavate to holocavate. Four prominent round lobes or protuberances are present, two on the epicyst and two on the hypocyst. The lobes are virtually identical in size and shape, imparting longitudinal symmetry to the cyst. However the lobes in the epicyst may be larger than the lobes of the hypocyst and vice versa; the species is rarely symmetrical about the equator.
The autophragm is about 1 µm thick and covered by dominantly nontabular, short, solid processes which are distally truncate, buccinate or capitate. The processes are between 0.5 and 1 µm in width and vary between being isolated, up to 2.5 µm apart, to extremely closely spaced. In forms with densely packed processes, individual elements are connected distally forming an ectophragm. Holocavate specimens may have a microreticulate appearance due to the network formed by distally –expanded process tips beneath the ectophragm.
Typically the width of the archaeopyle is twice the height.
Some short, discontinuous lineations of processes appear to be parasutural or penitabular.
The paracingulum and parasulcus are marked by a deep equatorial constriction and a narrow depression respectively and generally lack processes.
Dimensions (µm, n=25) including ornamentation where appropriate: Min. (Mean) Max.
Length of cyst: 34 (40) 49
Maximum width of hypocyst: 25 (30) 36
Equatorial (paracingular) width: 16 (19) 28
Maximum width of epicyst: 26 (31) 36
Height of archaeopyle: 6 (8) 10
Width of archaeopyle: 12 (15) 20
Height of processes: 1 (2) 4
Remarks/Comments:
This species of Aidelocysta does not vary significantly in size. The shape, however, varies in that the epicyst or the hypocyst may be the widest part of the cyst. Specimens where the epicystal and hypocystal lobes are similar in size are relatively rare. It also exhibits considerable variability in ornament type, length and density. The short processes may be distally truncate, buccinate or most commonly capitate. They are also sparsely to densely spaced, with occasional specimens having differentiated autophragm. Forms with dense processes are frequently holocavate. Occasionally, some areas of this species may have discontinuous lineations of processes which are either parasutural or penitabular. A full paratabulation pattern, however, has not been observed. Compression of the autophragm distorts the shape of the archaeopyle to ellipsoidal in some specimens.
Affinities/Comparison:
This species is distinguished by its quadrilobate shape, lack of polar horns and subpolar, peridiniacean style, anterior intercalary archaeopyle. Aidelocysta is currently monotypic and therefore generic comparisons also apply here. Species of Tetrachacysta such as T. allenii Backhouse 1988, T. baculata Backhouse 1988 and T . spinosigibberosa (Brideaux & Fisher 1976) Backhouse 1988 closely resemble A. clavata, but are distinguished by their apical archaeopyles.
Holotype: Riding and Helby, 2001g, figs.1I-L.
Type locaility: conventional core sample in Wanaea-2 well at 2880.50m.
Stratigraphical distribution: ranges from the Tithonian upper dingodinium jurassicum Zone (5aii) tot the Berriasian Kalyptea wisemaniae Zone (4biii)
Age: Tithonian-Berriasian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description [Riding & Helby, 2001g]:
Description:
A species of Aidelocysta which may be acavate to holocavate. Four prominent round lobes or protuberances are present, two on the epicyst and two on the hypocyst. The lobes are virtually identical in size and shape, imparting longitudinal symmetry to the cyst. However the lobes in the epicyst may be larger than the lobes of the hypocyst and vice versa; the species is rarely symmetrical about the equator.
The autophragm is about 1 µm thick and covered by dominantly nontabular, short, solid processes which are distally truncate, buccinate or capitate. The processes are between 0.5 and 1 µm in width and vary between being isolated, up to 2.5 µm apart, to extremely closely spaced. In forms with densely packed processes, individual elements are connected distally forming an ectophragm. Holocavate specimens may have a microreticulate appearance due to the network formed by distally –expanded process tips beneath the ectophragm.
Typically the width of the archaeopyle is twice the height.
Some short, discontinuous lineations of processes appear to be parasutural or penitabular.
The paracingulum and parasulcus are marked by a deep equatorial constriction and a narrow depression respectively and generally lack processes.
Dimensions (µm, n=25) including ornamentation where appropriate: Min. (Mean) Max.
Length of cyst: 34 (40) 49
Maximum width of hypocyst: 25 (30) 36
Equatorial (paracingular) width: 16 (19) 28
Maximum width of epicyst: 26 (31) 36
Height of archaeopyle: 6 (8) 10
Width of archaeopyle: 12 (15) 20
Height of processes: 1 (2) 4
Remarks/Comments:
This species of Aidelocysta does not vary significantly in size. The shape, however, varies in that the epicyst or the hypocyst may be the widest part of the cyst. Specimens where the epicystal and hypocystal lobes are similar in size are relatively rare. It also exhibits considerable variability in ornament type, length and density. The short processes may be distally truncate, buccinate or most commonly capitate. They are also sparsely to densely spaced, with occasional specimens having differentiated autophragm. Forms with dense processes are frequently holocavate. Occasionally, some areas of this species may have discontinuous lineations of processes which are either parasutural or penitabular. A full paratabulation pattern, however, has not been observed. Compression of the autophragm distorts the shape of the archaeopyle to ellipsoidal in some specimens.
Affinities/Comparison:
This species is distinguished by its quadrilobate shape, lack of polar horns and subpolar, peridiniacean style, anterior intercalary archaeopyle. Aidelocysta is currently monotypic and therefore generic comparisons also apply here. Species of Tetrachacysta such as T. allenii Backhouse 1988, T. baculata Backhouse 1988 and T . spinosigibberosa (Brideaux & Fisher 1976) Backhouse 1988 closely resemble A. clavata, but are distinguished by their apical archaeopyles.