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Achomosphaera sagena
From Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates:
[Achomosphaera sagena, Davey and Williams, 1966a, p. 51, pl.2, figs.1-2
May (1980, p.64) considered Hystrichosphaera (now Spiniferites) crassipellis to be the possible taxonomic senior synonym of this species. N.I.A.
Holotype: Davey and Williams, 1966a, pl.2, figs.1-2]
Locus typicus: Fetcham Mill, Surrey, England
Age: Cenomanian
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Original description: [Davey and Williams, 1966, p. 51]:
Diagnosis:
Wall of central body extremely thick, apparently composed of columar elements, surface coarsely reticulate. Closed gonal processes hollow, trifurcate with bifurcate extremities, and commonly possessing reticulate bases. Processes sometimes branched, branding mainly confined to cingular zone. Characteristically shaped precingular archaeopyle often present.
Description:
The wall of the central body, which may be up to 5 µm thick, is composed of elongate cellular elements lying perpendicular to the surface. The surface reticulation is coarse and may be up to 15 µm across.
Dimensions:
Holotype: diameter of central body 48 µm, length of processes up to 20 µm.
Range: diameter of central body 35-59 µm, length of processes up to 28 µm.
Affinities:
A. sagena is similar to H. crassipellis (Deflandre & Cookson) in that both possess thick walls of an identical nature with a reticulate surface. However sutural crests are absent in A. sagena.
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Supplemental descriptions:
Hultberg, 1985, p. 108-109:
Description:
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of the endophragm is smooth. The surface of the periphragm is granulate to slightly rugulate. The shape of the cyst is subspherical.
The ornamentation consists of slender processes at gonal and intergonal positions.
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Gocht, 1969, p. 36: (Translation: Geological Survey of Canada):
Description/Affinities:
The spherical main body has a thick wall with a fibrose radial structure and surface granulations. Especially on the dorsal half, there may be indications of a cingulum, with the rhomboid fields which are also characteristic for Hystrichosphaera. Frequently the process bases are joined to form lines; however, they do not form sharp lists bounding the fields. The sulcal region may be manifested as an elongate, triangular field. Also the poles are marked by roundish or 4- or 5-angled fields. The processes are hollow structures of the external membrane, with slender shafts which usually widen towards the base, but without affecting the globose form of the main body. The process shape is somewhat variable, but overall, characteristic. Usually the processes fork into three branches in the upper third, and each branch divides again distally. Perforations of the shaft and reticulation of the base, as described by Davey and Williams, 1966, do not occur. In the upper strata of the Early Eocene, there is a tendency toward forms with wider process bases and shorter branches. Forms of this latter type lead to the thick-walled Hystrichosphaera form described above as cf. crassipellis. They show distinct areation and sutural ribs. Davey and Williams also note the similarity of A. sagena to H. crassipellis. The difference compared to the English form- as far as one can judge from the description and the not very good illustrations- is in the type of outer membrane.
Dimensions:
Maximal extension 106-137 µm; main body diameter 65-80 µm.
Occurrence: Early Eocene.
[Achomosphaera sagena, Davey and Williams, 1966a, p. 51, pl.2, figs.1-2
May (1980, p.64) considered Hystrichosphaera (now Spiniferites) crassipellis to be the possible taxonomic senior synonym of this species. N.I.A.
Holotype: Davey and Williams, 1966a, pl.2, figs.1-2]
Locus typicus: Fetcham Mill, Surrey, England
Age: Cenomanian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Davey and Williams, 1966, p. 51]:
Diagnosis:
Wall of central body extremely thick, apparently composed of columar elements, surface coarsely reticulate. Closed gonal processes hollow, trifurcate with bifurcate extremities, and commonly possessing reticulate bases. Processes sometimes branched, branding mainly confined to cingular zone. Characteristically shaped precingular archaeopyle often present.
Description:
The wall of the central body, which may be up to 5 µm thick, is composed of elongate cellular elements lying perpendicular to the surface. The surface reticulation is coarse and may be up to 15 µm across.
Dimensions:
Holotype: diameter of central body 48 µm, length of processes up to 20 µm.
Range: diameter of central body 35-59 µm, length of processes up to 28 µm.
Affinities:
A. sagena is similar to H. crassipellis (Deflandre & Cookson) in that both possess thick walls of an identical nature with a reticulate surface. However sutural crests are absent in A. sagena.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Supplemental descriptions:
Hultberg, 1985, p. 108-109:
Description:
Chorate cyst, composed of endophragm and periphragm, closely appressed between processes. The surface of the endophragm is smooth. The surface of the periphragm is granulate to slightly rugulate. The shape of the cyst is subspherical.
The ornamentation consists of slender processes at gonal and intergonal positions.
----------------------------------------------
Gocht, 1969, p. 36: (Translation: Geological Survey of Canada):
Description/Affinities:
The spherical main body has a thick wall with a fibrose radial structure and surface granulations. Especially on the dorsal half, there may be indications of a cingulum, with the rhomboid fields which are also characteristic for Hystrichosphaera. Frequently the process bases are joined to form lines; however, they do not form sharp lists bounding the fields. The sulcal region may be manifested as an elongate, triangular field. Also the poles are marked by roundish or 4- or 5-angled fields. The processes are hollow structures of the external membrane, with slender shafts which usually widen towards the base, but without affecting the globose form of the main body. The process shape is somewhat variable, but overall, characteristic. Usually the processes fork into three branches in the upper third, and each branch divides again distally. Perforations of the shaft and reticulation of the base, as described by Davey and Williams, 1966, do not occur. In the upper strata of the Early Eocene, there is a tendency toward forms with wider process bases and shorter branches. Forms of this latter type lead to the thick-walled Hystrichosphaera form described above as cf. crassipellis. They show distinct areation and sutural ribs. Davey and Williams also note the similarity of A. sagena to H. crassipellis. The difference compared to the English form- as far as one can judge from the description and the not very good illustrations- is in the type of outer membrane.
Dimensions:
Maximal extension 106-137 µm; main body diameter 65-80 µm.
Occurrence: Early Eocene.