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Achomosphaera argesensis
From Fensome et al., 2019:
Achomosphaera argesensis, Demetresçu, 1989, p.51–54, pl.1, figs.1–6; pl.2, figs.1–4; text-fig.2; text-figs.3A–E.
Holotype: Demetresçu, 1989, pl.1, figs.1–5; text-fig.2; text-figs.3A,C.
Age: Early Pliocene.
Paratype: Demetresçu, 1989, L.P.B.-V-0257. Plate 2, 1-4. (The differences between these two forms are shown in Fig.3A-E. The holotype is lodged in the Paleontology Laboratory, University of Bucharest.)
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Original description: [Demetresçu, 1989]:
Diagnosis:
Ovoidal, slightly biconical dinoflagellate cysts, without any trace of parasutures, ridges or septa having a variably defined apical protrusion.
The wall is two-layered with a smooth periphragm, usually bearing 24 lobate branched and/or fenestrate gonal processes which do not communicate with the interior of the cyst. Typically, a large, flattened process always occurs in the apical region and may also be present in the antapical one.
Paracingulum spiral. Parasulcus undivided, more or less straight.
A gonyaulacacean formula of 4', 6", 6c, 5-?6'", lp, 1"", ?Xs is inferred.
Archeopyle precingular, Type P.
Dimensions:
Cyst length: 48 µm; width: 35 µm; thickness: 34 µm. apical protrusion: 5 µm. Process' length: 22 μm.
Range: Cyst length: 47- 50 μm; width: 32-35 µm; thickness: 33-35 µm. Apical protrusion: 1-71µm. Process' length: 15-26 µm; distal end: 2 40 μm.
Remarks:
The non-trifurcate character and the constant presence of a flat process developed on the apical area or on both apical and antapical areas differentiates A. argesensis from any other species of the genus. It differs from A. ramulifera (Deflandre) Evitt 1963 in having a horn-like apical protrusion, by which it resembles A. improcera (Islam 1983) and Spiniferites bentori (Rossignol) Wall and Dale 1970, but differs from the former in having much longer processes, and from the latter in lacking parasutural marks. A species apparently resembling A. argesensis would be A. andalousiensis Jan du Ch6ne, 1977, but this one does not possess processes with lobate tips and a flat apical process either. Even though Spiniferites should include only species with well-defined parasutural features, there are forms showing no such characters such as S. validus Szentai 1982, which also resembles A. argesensis in having no paratabulation. Yet it differs from this new species in possessing a thin, elongated apical peak, instead of a flattened, large process as A. argesensis exhibits. Let us point out again the absence of the trifurcate character. Taking into account this aspect, it is worth to note that Evitt (1985, p.221) clearly stated that: "The common denominator for the Spiniferites complex (which includes Achomosphaera), is ... a trifurcate process ...", a character not present in A. argesensis. If this is the case, the concept of this complex, as well as the generic definition of Achomosphaera should be revised in order to accommodate such forms (i.e. specimens without trifurcate processes) and to consider the presence or absence of trifurcate processes as a specific rather than a generic criterion. Otherwise, A. argesensis would entail the creation of a new genus that will incorporate particularly such specimens. Occurrence: Recorded from Beceni, Curtea de Arges and Berbesti surface sections. It was also observed in Ticleni wells samples. The age is considered to be earliest late Dacian, which might correspond to the Tabianian base in the Standard Mediterranean stages.
Achomosphaera argesensis, Demetresçu, 1989, p.51–54, pl.1, figs.1–6; pl.2, figs.1–4; text-fig.2; text-figs.3A–E.
Holotype: Demetresçu, 1989, pl.1, figs.1–5; text-fig.2; text-figs.3A,C.
Age: Early Pliocene.
Paratype: Demetresçu, 1989, L.P.B.-V-0257. Plate 2, 1-4. (The differences between these two forms are shown in Fig.3A-E. The holotype is lodged in the Paleontology Laboratory, University of Bucharest.)
---------------------------------------------------------------------------------------------------
Original description: [Demetresçu, 1989]:
Diagnosis:
Ovoidal, slightly biconical dinoflagellate cysts, without any trace of parasutures, ridges or septa having a variably defined apical protrusion.
The wall is two-layered with a smooth periphragm, usually bearing 24 lobate branched and/or fenestrate gonal processes which do not communicate with the interior of the cyst. Typically, a large, flattened process always occurs in the apical region and may also be present in the antapical one.
Paracingulum spiral. Parasulcus undivided, more or less straight.
A gonyaulacacean formula of 4', 6", 6c, 5-?6'", lp, 1"", ?Xs is inferred.
Archeopyle precingular, Type P.
Dimensions:
Cyst length: 48 µm; width: 35 µm; thickness: 34 µm. apical protrusion: 5 µm. Process' length: 22 μm.
Range: Cyst length: 47- 50 μm; width: 32-35 µm; thickness: 33-35 µm. Apical protrusion: 1-71µm. Process' length: 15-26 µm; distal end: 2 40 μm.
Remarks:
The non-trifurcate character and the constant presence of a flat process developed on the apical area or on both apical and antapical areas differentiates A. argesensis from any other species of the genus. It differs from A. ramulifera (Deflandre) Evitt 1963 in having a horn-like apical protrusion, by which it resembles A. improcera (Islam 1983) and Spiniferites bentori (Rossignol) Wall and Dale 1970, but differs from the former in having much longer processes, and from the latter in lacking parasutural marks. A species apparently resembling A. argesensis would be A. andalousiensis Jan du Ch6ne, 1977, but this one does not possess processes with lobate tips and a flat apical process either. Even though Spiniferites should include only species with well-defined parasutural features, there are forms showing no such characters such as S. validus Szentai 1982, which also resembles A. argesensis in having no paratabulation. Yet it differs from this new species in possessing a thin, elongated apical peak, instead of a flattened, large process as A. argesensis exhibits. Let us point out again the absence of the trifurcate character. Taking into account this aspect, it is worth to note that Evitt (1985, p.221) clearly stated that: "The common denominator for the Spiniferites complex (which includes Achomosphaera), is ... a trifurcate process ...", a character not present in A. argesensis. If this is the case, the concept of this complex, as well as the generic definition of Achomosphaera should be revised in order to accommodate such forms (i.e. specimens without trifurcate processes) and to consider the presence or absence of trifurcate processes as a specific rather than a generic criterion. Otherwise, A. argesensis would entail the creation of a new genus that will incorporate particularly such specimens. Occurrence: Recorded from Beceni, Curtea de Arges and Berbesti surface sections. It was also observed in Ticleni wells samples. The age is considered to be earliest late Dacian, which might correspond to the Tabianian base in the Standard Mediterranean stages.