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Aquadulcum yangchepense
Aquadulcum? yanchepense, Harland and Sarjeant, 1970
Harland and Sarjeant, 1970, questionably included this species in Aquadulcum.
Holotype: Harland and Sarjeant, 1970, pl.22, fig.3
Locus typicus: Yanchep Swamp, north of Perth, Western Australia
Stratum typicum: Holocene (post-Atlantic, not precisely dated)
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Original description: [Harland and Sarjeant, 1970, p. 222]:
Diagnosis:
Cyst broadly ovoidal in outline, with rounded conical epitract and almost hemispherical hypotract. Wall of moderate thickness, possibly composed of a single layer only, markedly granular and giving rise to some sixty short, rather stubby processes. The arrangement of the processes, along the borders of the cingulum and in lines elsewhere, suggests that they may be sutural in character. Each process tapers from a broad base to about mid-point, then flares to the tips; the process tips are branched, the branches being of unequal length, and the branches themselves may bifurcate. Their length is up to about one-sixth of the short diameter of the shell.
The cingulum is broad, slightly sunken and devoid of processes; it is laevorotatory, the two ends differing in antero-posterior position by the cingulum"s breadth.
The sulcus is narrower and rather poorly marked.
An apical opening was observed in the holotype but was not constantly observed in all specimens.
Dimensions:
Holotype: Length 52 µm, breadth 46 µm. Other specimens of closely similar dimensions.
Affinities and Remark: (p. 223):
These microfossils were originally very tentatively described as "Organism No. 2", by Churchill and Sarjeant, 1963. Their re-examination affords no room for doubt that these are dinoflagellate cysts.
In the holotype, and in some other specimens, a distinct apical opening was present, in the form of a polygonal, rather elongate slit with a V-shaped end aligned on the sulcus and a corresponding V-shaped end on the dorsal surface. This opening is smaller in size than a typical A apical archaeopyle and quite dissimilar in outline: if it is indeed to be regarded as a form of apical archaeopyle (as seems probable), it may be formed by the loss of the equivalent of plate 1" and one other apical plate, rather than by the loss of the equivalent of the whole apical plate series.
The generic assignment of this species is problematical: in that only one type of process is present, it differs from the genus Cobricosphaeridium, and in the possible development of an apical archaeopyle, it differs from the genus Aquadulcum. The character of the apical opening differentiates it from the genus Tenua (not hitherto recorded from post-Mesozoic sediments). If more extended studies confirm the constancy of the archaeopyle and its distinctive character (not all specimens originally examined were available for re-study) then the erection of a separate genus may prove desirable.
Harland and Sarjeant, 1970, questionably included this species in Aquadulcum.
Holotype: Harland and Sarjeant, 1970, pl.22, fig.3
Locus typicus: Yanchep Swamp, north of Perth, Western Australia
Stratum typicum: Holocene (post-Atlantic, not precisely dated)
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Harland and Sarjeant, 1970, p. 222]:
Diagnosis:
Cyst broadly ovoidal in outline, with rounded conical epitract and almost hemispherical hypotract. Wall of moderate thickness, possibly composed of a single layer only, markedly granular and giving rise to some sixty short, rather stubby processes. The arrangement of the processes, along the borders of the cingulum and in lines elsewhere, suggests that they may be sutural in character. Each process tapers from a broad base to about mid-point, then flares to the tips; the process tips are branched, the branches being of unequal length, and the branches themselves may bifurcate. Their length is up to about one-sixth of the short diameter of the shell.
The cingulum is broad, slightly sunken and devoid of processes; it is laevorotatory, the two ends differing in antero-posterior position by the cingulum"s breadth.
The sulcus is narrower and rather poorly marked.
An apical opening was observed in the holotype but was not constantly observed in all specimens.
Dimensions:
Holotype: Length 52 µm, breadth 46 µm. Other specimens of closely similar dimensions.
Affinities and Remark: (p. 223):
These microfossils were originally very tentatively described as "Organism No. 2", by Churchill and Sarjeant, 1963. Their re-examination affords no room for doubt that these are dinoflagellate cysts.
In the holotype, and in some other specimens, a distinct apical opening was present, in the form of a polygonal, rather elongate slit with a V-shaped end aligned on the sulcus and a corresponding V-shaped end on the dorsal surface. This opening is smaller in size than a typical A apical archaeopyle and quite dissimilar in outline: if it is indeed to be regarded as a form of apical archaeopyle (as seems probable), it may be formed by the loss of the equivalent of plate 1" and one other apical plate, rather than by the loss of the equivalent of the whole apical plate series.
The generic assignment of this species is problematical: in that only one type of process is present, it differs from the genus Cobricosphaeridium, and in the possible development of an apical archaeopyle, it differs from the genus Aquadulcum. The character of the apical opening differentiates it from the genus Tenua (not hitherto recorded from post-Mesozoic sediments). If more extended studies confirm the constancy of the archaeopyle and its distinctive character (not all specimens originally examined were available for re-study) then the erection of a separate genus may prove desirable.