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Achomosphaera antleriformis
Williams, Lentin and Fensome 1998 - Lentin and Williams Index of Fossil Dinoflagellates
Achomosphaera antleriformis, Schiøler, 1993, p. 102,104, pl.3, figs.1–6; text-figs.2a–c
Holotype: Schiøler, 1993, pl.3, fig.2; text-figs.2a-b
Paratype: Schioler, 1993
Locus typicus: Well M-lx, depth 1936.1m, Dan Field, Danish North Sea
Age: Maastrichtian.
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Original description: [Schioler, 1993, p. 102-104]:
Diagnosis:
A skolochorate gonyaulacoid cyst which lacks indications of sutures between the processes. The processes are gonal, long-stemmed and straight, with wide, robust bi- or trifurcations which give rise to secondary furcations that are truncated terminally.
Description:
Large skolochorate cyst. Periphragm and endophragm appressed between processes.
The cyst body is ovoidal to subspherical.
The periphragm and endophragm are smooth.
The processes are gonal, hollow and closed; process length approximately equals the endocystal radius. The processes have slender stems that expand distally in broad primary trifurcations followed by secondary bi- or trifurcations, resembling the antlers of a deer. Text-fig. 2 shows a selection of typical process types on A. antleriformis sp. nov. The width of the process terminations of the largest processes approximately equals the radius of the endocyst. The stems of the apical processes are sometimes connected by septa of variable height, forming a single polar process complex with four trifurcate terminations (Pl. 3, figs 2,5, textfig. 3a).
Archaeopyle type P(3), operculum free. Paracingulum and parasulcus not visible.
Paratabulation gonyaulacoid, suggested by the position of the processes.
Dimensions (in µm): holotype range
overall length: 107 101 (111) 130
overall width: 93 87 (100) 110
length of endocyst: 61 58 (61) 78
width of endocyst: 49 44 (54) 78
process length: 23 - 29 20 - 32
Specimens measured: 7
Affinities:
Achomosphaera antleriformis is separated from the subspecies of Achomosphaera ramulifera (Deflandre 1937) Evitt 1963 by its more robust and truncated process terminations. A. antleriformis furthermore has narrower process stems than Achomosphaera ramulifera ramulifera (Deflandre 1937) Evitt 1963, and twice as long processes as Achomosphaera ramulifera gabonensis (Boltenhagen 1977) Lentin and Williams 1981.
Achomosphaera ramulifera perforata (Davey and Williams 1966) Lentin and Williams 1973 is separated from the new species by its fenestrate processes. Achomosphaera fenestrata Kirsch 1991 differs from the new species in having open processes with striate process stems and a perforated membrane connecting the distal furcations of each process. Achomosphaera alcicornu (Eisenack 1954) Davey and Williams 1966 differs in having open processes which terminate trifurcating and funnel-shaped. Hansen (1977, fig. 17f) illustrated a specimen of the latter species from the Danian of Denmark which has a superficial resemblance to the new species; his specimen can be differentiated by the lack of distinct branching of the process terminations and the presence of faint sutures between the process bases.
Achomosphaera antleriformis, Schiøler, 1993, p. 102,104, pl.3, figs.1–6; text-figs.2a–c
Holotype: Schiøler, 1993, pl.3, fig.2; text-figs.2a-b
Paratype: Schioler, 1993
Locus typicus: Well M-lx, depth 1936.1m, Dan Field, Danish North Sea
Age: Maastrichtian.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Schioler, 1993, p. 102-104]:
Diagnosis:
A skolochorate gonyaulacoid cyst which lacks indications of sutures between the processes. The processes are gonal, long-stemmed and straight, with wide, robust bi- or trifurcations which give rise to secondary furcations that are truncated terminally.
Description:
Large skolochorate cyst. Periphragm and endophragm appressed between processes.
The cyst body is ovoidal to subspherical.
The periphragm and endophragm are smooth.
The processes are gonal, hollow and closed; process length approximately equals the endocystal radius. The processes have slender stems that expand distally in broad primary trifurcations followed by secondary bi- or trifurcations, resembling the antlers of a deer. Text-fig. 2 shows a selection of typical process types on A. antleriformis sp. nov. The width of the process terminations of the largest processes approximately equals the radius of the endocyst. The stems of the apical processes are sometimes connected by septa of variable height, forming a single polar process complex with four trifurcate terminations (Pl. 3, figs 2,5, textfig. 3a).
Archaeopyle type P(3), operculum free. Paracingulum and parasulcus not visible.
Paratabulation gonyaulacoid, suggested by the position of the processes.
Dimensions (in µm): holotype range
overall length: 107 101 (111) 130
overall width: 93 87 (100) 110
length of endocyst: 61 58 (61) 78
width of endocyst: 49 44 (54) 78
process length: 23 - 29 20 - 32
Specimens measured: 7
Affinities:
Achomosphaera antleriformis is separated from the subspecies of Achomosphaera ramulifera (Deflandre 1937) Evitt 1963 by its more robust and truncated process terminations. A. antleriformis furthermore has narrower process stems than Achomosphaera ramulifera ramulifera (Deflandre 1937) Evitt 1963, and twice as long processes as Achomosphaera ramulifera gabonensis (Boltenhagen 1977) Lentin and Williams 1981.
Achomosphaera ramulifera perforata (Davey and Williams 1966) Lentin and Williams 1973 is separated from the new species by its fenestrate processes. Achomosphaera fenestrata Kirsch 1991 differs from the new species in having open processes with striate process stems and a perforated membrane connecting the distal furcations of each process. Achomosphaera alcicornu (Eisenack 1954) Davey and Williams 1966 differs in having open processes which terminate trifurcating and funnel-shaped. Hansen (1977, fig. 17f) illustrated a specimen of the latter species from the Danian of Denmark which has a superficial resemblance to the new species; his specimen can be differentiated by the lack of distinct branching of the process terminations and the presence of faint sutures between the process bases.