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Microdinium cretaceum
Microdinium cretaceum Slimani, 1994, p.30-32, pl.6, figs.1-4,18-21.
Taxonomic junior synonym: Microdinium ovatum Wilson (name not validly published), according to Slimani (2001a, p.193).
Holotype: Slimani, 1994, pl.6, figs.1-3,18-19.
Age: Maastrichtian.
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Original description (Slimani, 1994) (translated from French):
Microdinium cretaceum sp. nov. (PI.6, Fig.1-4, 18-21)
Name derivation: Cretaceous, referring to the age of this species (Campanian-Maastrichtian).
Holiday: Turnhout -864.60 m, preparation 7, E.F. coord. W35.
Type locality: Turnhout -864.60 m.
Type horizon: Maastrichtian.
Synonymy:
1974: Mirodinium ovatum in WILSON, pp. 263-264, pl. 12, fig. 10-12.
1976: Genus A-BENSON, pp. 222, 224; pl. 13; fig. 10-12; pl. 14, fig. 1.
1977: Microdinium cf. ovatum Wilson unpublished - Schumacker-Lambry in Streel et al., pl. 3, fig. 13.
1992: Phanerodinium sonciniae - MARHEINECKE, pl. 25, fig. 3-4.
Diagnosis: Proximate cyst, ovoidal to subspheroidal, with an epicyst half as long as the hypocyst, bears smooth and well-developed parasutural ridges that reflect a complete paratabulation of the gonyaulacoid type. Conforming to the formula: lpr, 4', 4a, 6", 6c, 6"', lp, 1"", 2 - 5s. The wall is double-membranous with a distinct periphragm and supported by intratabular structures that are often materialized by a single central process per plate. The archaeopyle is apical and intercalary, type (tAtl)a, with a ventrally attached operculum.
Dimensions: Holotype. Maximum diameter: 30 µm. Variations, maximum diameter: 28-36 µm. Number of specimens measured: 10.
Material: > 80 specimens.
Description: The thick endophragm (approximately 1-1.5 µm) is smooth; the thinner periphragm is transparent and smooth. The intratabular processes are one or rarely two per plate, located centrally; they are often pillar-like or slightly bifid distally. The parasutural ridges are 2-4 µm high. Paraplate 1"' is larger than paraplate 1p; their outlines are hexagonal and pentagonal, respectively, and they are arranged with the other paraplates of the hypocyst in a partiform configuration. The parasulcus is divided into 2 to 5 paraplates; the posterior sulcal paraplate is wide and subomegaform. The paracingulum (6 to 10 µm wide) is very slightly laevorotatory or non-spiral and often lacks intratabular processes. The archaeopyle is small (10 to 12 µm). The operculum is composed of 9 paraplates, including 1 preapical, 4 apical, and 4 anterior intercalary.
Comparison: Microdinium cretaceum sp. nov. is very comparable to the specimens listed under the name Microdinium ovatum in Wilson's unpublished work (1974); the specimens of Phanerodinium sonciniae MARHEINECKE (1992: pl. 25, fig. 3, 4) from the Maastrichtian of Hemmoor (Germany), exhibit a morphology apparently similar to that of the present species. Genus A of BENSON (1976) is probably represented by the same cyst type, but the type of its archaeopyle has not been defined due to its state of preservation. The broad paracingulum, the small (tAtl)a type archaeopyle, and the partiform arrangement of the hypocystal region in M. cretaceum sp. nov. mark a significant difference from Membranigonyaulax wilsonii sp. nov., which is characterized by a less broad paracingulum, a broad (tA) type archaeopyle with a deep sulcal notch, and has a quinqueform hypocystal configuration. Stratigraphic distribution: Turnhout: -966.50 to -722.40 m, Upper Campanian. - Danien. In WILSON (1974), Maastrichtian inf. (occidentalis and lanceolata Zone - Western Zone), Denmark. BENSON (1976), Maastrichtian, Maryland, U.S.A. SCHUMACKER-LAMBRY in STREEL et al. (1977), Campanian, N.E. of Belgium.
Taxonomic junior synonym: Microdinium ovatum Wilson (name not validly published), according to Slimani (2001a, p.193).
Holotype: Slimani, 1994, pl.6, figs.1-3,18-19.
Age: Maastrichtian.
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Original description (Slimani, 1994) (translated from French):
Microdinium cretaceum sp. nov. (PI.6, Fig.1-4, 18-21)
Name derivation: Cretaceous, referring to the age of this species (Campanian-Maastrichtian).
Holiday: Turnhout -864.60 m, preparation 7, E.F. coord. W35.
Type locality: Turnhout -864.60 m.
Type horizon: Maastrichtian.
Synonymy:
1974: Mirodinium ovatum in WILSON, pp. 263-264, pl. 12, fig. 10-12.
1976: Genus A-BENSON, pp. 222, 224; pl. 13; fig. 10-12; pl. 14, fig. 1.
1977: Microdinium cf. ovatum Wilson unpublished - Schumacker-Lambry in Streel et al., pl. 3, fig. 13.
1992: Phanerodinium sonciniae - MARHEINECKE, pl. 25, fig. 3-4.
Diagnosis: Proximate cyst, ovoidal to subspheroidal, with an epicyst half as long as the hypocyst, bears smooth and well-developed parasutural ridges that reflect a complete paratabulation of the gonyaulacoid type. Conforming to the formula: lpr, 4', 4a, 6", 6c, 6"', lp, 1"", 2 - 5s. The wall is double-membranous with a distinct periphragm and supported by intratabular structures that are often materialized by a single central process per plate. The archaeopyle is apical and intercalary, type (tAtl)a, with a ventrally attached operculum.
Dimensions: Holotype. Maximum diameter: 30 µm. Variations, maximum diameter: 28-36 µm. Number of specimens measured: 10.
Material: > 80 specimens.
Description: The thick endophragm (approximately 1-1.5 µm) is smooth; the thinner periphragm is transparent and smooth. The intratabular processes are one or rarely two per plate, located centrally; they are often pillar-like or slightly bifid distally. The parasutural ridges are 2-4 µm high. Paraplate 1"' is larger than paraplate 1p; their outlines are hexagonal and pentagonal, respectively, and they are arranged with the other paraplates of the hypocyst in a partiform configuration. The parasulcus is divided into 2 to 5 paraplates; the posterior sulcal paraplate is wide and subomegaform. The paracingulum (6 to 10 µm wide) is very slightly laevorotatory or non-spiral and often lacks intratabular processes. The archaeopyle is small (10 to 12 µm). The operculum is composed of 9 paraplates, including 1 preapical, 4 apical, and 4 anterior intercalary.
Comparison: Microdinium cretaceum sp. nov. is very comparable to the specimens listed under the name Microdinium ovatum in Wilson's unpublished work (1974); the specimens of Phanerodinium sonciniae MARHEINECKE (1992: pl. 25, fig. 3, 4) from the Maastrichtian of Hemmoor (Germany), exhibit a morphology apparently similar to that of the present species. Genus A of BENSON (1976) is probably represented by the same cyst type, but the type of its archaeopyle has not been defined due to its state of preservation. The broad paracingulum, the small (tAtl)a type archaeopyle, and the partiform arrangement of the hypocystal region in M. cretaceum sp. nov. mark a significant difference from Membranigonyaulax wilsonii sp. nov., which is characterized by a less broad paracingulum, a broad (tA) type archaeopyle with a deep sulcal notch, and has a quinqueform hypocystal configuration. Stratigraphic distribution: Turnhout: -966.50 to -722.40 m, Upper Campanian. - Danien. In WILSON (1974), Maastrichtian inf. (occidentalis and lanceolata Zone - Western Zone), Denmark. BENSON (1976), Maastrichtian, Maryland, U.S.A. SCHUMACKER-LAMBRY in STREEL et al. (1977), Campanian, N.E. of Belgium.