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Apteodinium tectatum
Apteodinium tectatum, Piasecki, 1980
Taxonomic senior synonym: Apteodinium spiridoides, according to Lucas-Clark (1987, p.178) - however, Jan du Chêne in Head and Wrenn (1992, p.3) retained Apteodinium tectatum.
Holotype: Piasecki, 1980, pl.2, fig.4-6; Jan du Chêne et al., 1986, pl.10, figs.5-8
Paratypes: Piasecki, 1980
Locus typicus: Hodde Fm., Gram Bore (DGU file 141423), Gram, Denmark
Stratum typicum: Middle Miocene
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Original description: [Piasecki, 1980, p. 63-66]:
Diagnosis:
Spherical to ovoidal Apteodinium with a short and broad apical horn. The wall is differentiated into three units. The middle unit consists either of spongeous tissue with internal channels or short "processes" separating the inner and outer unit.
Paracingulum and parasulcus are clearly differentiated.
The archaeopyle is precingular: Type P.
Description (annotated):
The endophragma is thick, massive and hyaline, and separated from the periphragma by short "processes", low walls or spongeous tissue with internal channels. All intermediate structures have been observed, but the wall structures are generally uniform in one specimen. The internal walls and processes are buccinate in optical sections because they are expanded proximately and distally. The periphragma is thin and finely foveolate. The thickness of the cyst wall varies from 2 to 6 µm. The apical horn is mainly formed by the periphragma and the middle wall unit, but a weak bulge may be present in the endophragma below the horn. The length of the apical horn varies from 2 to 14 µm. No parasutural structures have been observed, except for the thickenings of the middle wall unit along the sides of the paracingulum.
The paracingulum and the parasulcus are grooved and the structure of the middle wall unit may be absent in these areas. The paracingulum is helicoidal and narrow. The endo- and periphragma may be in contact in the parasulcal area.
The archaeopyle is pentagonal to trapezoidal and the posterior margin is in contact with the paracingulum. Shape and position of the archaeopyle is pentagonal to trapezoidal and the posterior margin is in contact with the paracingulum. Shape and position of the archaeopyle indicate that it is formed by the loss of paraplate 3"". The archaeopyle formula is P.
Affinities:
Apteodinium tectatum differs from other species of the genus by the combination of the helicoidal paracingulum, the presence of a well defined parasulcus, the apical horn and the wall structure. The genus Pyxidiella Cookson and Eisenack, 1958 has and intercalary archaeopyle and no apical horn. The homology of wall layers in dinoflagellate cysts is not well understood yet, and the terminology (Evitt et al., 1977) is therefore not always definitive. In this case the terminology of the wall layers is dependent on the interpretation of the middle wall unit. I have chosen to regard the wall cavity as being a reduced pericoel and to regard the structures of the middle wall unit as not being "regular processes", because the middle wall unit also appears as more common wall structure (spongeous), which may be a part of the periphragma. The inner and outer wall layers are therefore endo- and periphragm respectively. The wall of Dinopterygium verriculum which is discussed later in this paper, is interpreted in the same way.
Taxonomic senior synonym: Apteodinium spiridoides, according to Lucas-Clark (1987, p.178) - however, Jan du Chêne in Head and Wrenn (1992, p.3) retained Apteodinium tectatum.
Holotype: Piasecki, 1980, pl.2, fig.4-6; Jan du Chêne et al., 1986, pl.10, figs.5-8
Paratypes: Piasecki, 1980
Locus typicus: Hodde Fm., Gram Bore (DGU file 141423), Gram, Denmark
Stratum typicum: Middle Miocene
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Piasecki, 1980, p. 63-66]:
Diagnosis:
Spherical to ovoidal Apteodinium with a short and broad apical horn. The wall is differentiated into three units. The middle unit consists either of spongeous tissue with internal channels or short "processes" separating the inner and outer unit.
Paracingulum and parasulcus are clearly differentiated.
The archaeopyle is precingular: Type P.
Description (annotated):
The endophragma is thick, massive and hyaline, and separated from the periphragma by short "processes", low walls or spongeous tissue with internal channels. All intermediate structures have been observed, but the wall structures are generally uniform in one specimen. The internal walls and processes are buccinate in optical sections because they are expanded proximately and distally. The periphragma is thin and finely foveolate. The thickness of the cyst wall varies from 2 to 6 µm. The apical horn is mainly formed by the periphragma and the middle wall unit, but a weak bulge may be present in the endophragma below the horn. The length of the apical horn varies from 2 to 14 µm. No parasutural structures have been observed, except for the thickenings of the middle wall unit along the sides of the paracingulum.
The paracingulum and the parasulcus are grooved and the structure of the middle wall unit may be absent in these areas. The paracingulum is helicoidal and narrow. The endo- and periphragma may be in contact in the parasulcal area.
The archaeopyle is pentagonal to trapezoidal and the posterior margin is in contact with the paracingulum. Shape and position of the archaeopyle is pentagonal to trapezoidal and the posterior margin is in contact with the paracingulum. Shape and position of the archaeopyle indicate that it is formed by the loss of paraplate 3"". The archaeopyle formula is P.
Affinities:
Apteodinium tectatum differs from other species of the genus by the combination of the helicoidal paracingulum, the presence of a well defined parasulcus, the apical horn and the wall structure. The genus Pyxidiella Cookson and Eisenack, 1958 has and intercalary archaeopyle and no apical horn. The homology of wall layers in dinoflagellate cysts is not well understood yet, and the terminology (Evitt et al., 1977) is therefore not always definitive. In this case the terminology of the wall layers is dependent on the interpretation of the middle wall unit. I have chosen to regard the wall cavity as being a reduced pericoel and to regard the structures of the middle wall unit as not being "regular processes", because the middle wall unit also appears as more common wall structure (spongeous), which may be a part of the periphragma. The inner and outer wall layers are therefore endo- and periphragm respectively. The wall of Dinopterygium verriculum which is discussed later in this paper, is interpreted in the same way.